MSEL - NIST

MSELNational Institute ofStandards and Technology

Technology Administration

U.S. Department of Commerce

NISTIR 6796

September 2001

FY 2001 PROGRAMS AND ACCOMPLISHMENTS

POLYMERS DIVISION

Advance measurement methods to characterize microstructure failure in composites

This optical image is a planar array of glass fibers embedded in epoxy resin matrix deformed under tension. The arrays are used to investigate the failure initiation in fibrous composites. In the optical image, the fibers are spaced (30 to 45) mm apart and the dark regions along each fiber are cracks that extend into the surrounding polymer matrix. The light blue regions that connect the fiber breaks show high deformation shear bands that emanate from the tips of the matrix cracks.

National Institute ofStandards and TechnologyKaren H. Brown, Acting Director

TechnologyAdministration

U.S. Department ofCommerceDonald L. Evans, Secretary

MATERIALSSCIENCE AND ENGINEERINGLABORATORYFY 2001 PROGRAMS ANDACCOMPLISHMENTS

POLYMERSDIVISIONEric J. Amis, Chief

Bruno M. Fanconi, Deputy

NISTIR 6796

September 2001

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Executive Summary ............................................................................................................................................................. 1

Technical Highlights

Mass Spectrometry of Polyethylene ......................................................................................................................... 4Combinatorial Study of Surface Pattern Formation ................................................................................................... 6Measurement Methods Aid Development of Photoresists for Next-Generation Photolithography ......................... 8Polymer Mass Distribution by Mass Spectrometry .................................................................................................10Multi-Fiber Failure Propagation ...............................................................................................................................12Biocompatibility of a Moldable, Resorbable, Composite Bone Graft .......................................................................14The Mechanism of Sharkskin ...................................................................................................................................16

Projects and Programs

Combinatorial Methods .....................................................................................................................................................19

High-Throughput Measurements of Crystallization and Nucleation in Polyolefins ................................................20Combinatorial Mapping of Polymer Film Wettabilty ................................................................................................21Anisotropic Adhesion Between Polymers, Metals, Ceramics and Biomaterials ......................................................22Patterned Polymeric Substrates for Directed Cell Growth ........................................................................................23Microwell Arrays for Laser Capture Microdissection (LCM) ..................................................................................24Tissue Development in Co-extruded Polymer Scaffolds ..........................................................................................25

Interface of Materials with Biology ....................................................................................................................................26

The Dynamic Effects of Protein Stabilization in Glass Forming Liquids ..................................................................27Structure-Property Relationships in Dental Polymers ..............................................................................................28A Moldable, Resorbable, Macroporous, Composite Bone Graft Containing Growth Factor ...................................29Bioactive Polymeric Composites for Mineralized Tissue Regeneration ...................................................................30

Materials For Microelectronics ..........................................................................................................................................31

Characterization of Porous Low-k Dielectric Constant Thin Films ...........................................................................32Polymer Fundamentals of Photolithography ...........................................................................................................33Characterizing Buried Polymer/Substrate Interfaces ................................................................................................34

Materials For Wireless Communication .............................................................................................................................35

Dielectric Metrology for Polymer Composite Films in the Microwave Range ..........................................................36

Table of Contents

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Multiphase Polymeric Materials ........................................................................................................................................37

Constitutive Relationship of Polymer Blends for Process Modeling Needs ............................................................38Modeling of Interfaces and Interphases of Polymeric Systems ...............................................................................39Synergistic Interactions in Polymer-Nanoparticle Composites ................................................................................40Structure-Property Characterization and Modeling .................................................................................................41Mechanics of Fiber and Nano-Filled Composites ....................................................................................................42Poly-OOF: A Virtual Experimental Tool for Polymer Research ..................................................................................43

Polymer Characterization ...................................................................................................................................................44

Optical Coherence Tomography ..............................................................................................................................45Polyolefin Mass Spectrometry .................................................................................................................................46Fluorescent Sub-Micrometer Probe Molecules with Starlike Architecture ..............................................................47Standard Reference Materials ..................................................................................................................................48Quantitative Mass Spectrometry of Synthetic Polymers .........................................................................................49Support for the Biomaterials Integrated Products Industries ...................................................................................50Control of Extrusion Instabilities .............................................................................................................................51Real-Time Process Monitoring ................................................................................................................................52Micro-scale Processing ............................................................................................................................................53

Publications .......................................................................................................................................................................54

Staff and Organizational Structure

Polymers Division ....................................................................................................................................................62Research Staff ..........................................................................................................................................................63Organizational Charts ...............................................................................................................................................71

Certain commercial materials and equipment are identifiedin this report in order to specify adequately the experimen-tal procedures. In no case does such identification implyrecommedation or endorsement by the National Instituteof Standards and Technology nor does it imply necessar-ily the best available for the purpose.

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Executive Summary

The Polymers Division provides measurement methods,standards, and concepts to facilitate technology develop-ment, manufacture of products, commerce, and use ofsynthetic polymers. Projects are selected based on assess-ments of current needs and in anticipation of future needsas determined from topical workshops, industry roadmaps,as well as visits to companies and other research organiza-tions. Much of our work is performed collaboratively withcustomers. Over 35 companies, in addition to trade asso-ciations and other federal agencies participated in thework of the Division. The close interactions with custom-ers assure that the work remains focused.

The work of the Division is organized into three groupsthat focus on areas where synthetic polymers are exploitedfor their unique properties—electronics materials, light-weight structural materials, and biomedical materials. Twoother groups are concerned with needs that crosscut theapplications areas—better control of polymer processingand more rapid test methodology.

• The Division is building on the success of its effort tocharacterize properties of porous thin films under de-velopment as low-k dielectrics for use as interleveldielectric films in the next generation IC chips. The newmetrology we have developed received strong endorse-ments by both International SEMATECH and the Na-tional Research Council panel performing a crosscut-ting assessment of NIST programs in microelectronics.In anticipation of the needs of the microelectronicsindustry for measurement methods to identify charac-teristics of photoresist polymers that limit further re-ductions in feature size, the Division successfully usedneutron scattering to elucidate the shape of featuresproduced by photolithography. Other measurementstrategies are under development to determine howmacromolecular dynamics and other molecular charac-teristics are affected by the thickness of polymer thinfilms of the sort used in today’s photoresists.

• For structural applications polymeric materials are com-bined in manufacture with other materials, particulates,fibers or other polymers to achieve property enhance-ment, cost reduction and/or improved processibility.Although many successful products have been devel-oped it is recognized that future progress rests onimproving predictions of resultant properties fromconstituent properties, particularly at the molecularlevel. Our work in this area builds the connectionsbetween computer simulations of molecular behaviorand macroscopic properties. This year we developed anew instrumental method that characterizes how frac-ture of a single glass fiber affects failure processes of

neighboring fibers and the matrix resin in a fiber-rein-forced composite.

• Increasing use is made of synthetic polymers in humanimplants to restore body function and improve qualityof life. New therapies are under development throughtissue engineered products approaches. This year wedemonstrated the utility of a new approach to producea polymeric scaffold of controlled morphology bycoextrusion of incompatible polymers followed byleaching of one polymer to provide three-dimensionalconnected pores. Workshops this year with providersof medical products and services identified a prioritizedlist of needed reference biomaterials and data. TheDivision has responded by issuing the first NIST refer-ence biomaterial for orthopedic applications, a medicalgrade polyethylene that will be used for comparativestudies and for developing improved materials.

• The Polymers Division is pioneering the development ofcombinatorial methods to measure rapidly properties ofmaterials. The approach is similar to that used with agreat deal of success in the pharmaceutical industry indiscovery of new drugs. The key components of acombinatorial method are a sample in which composi-tion, film thickness or other characteristics are con-trolled, a technique to image the entire specimen forproperties of interest, optical microscopy, for example,and analysis techniques capable of treating exceed-ingly large amounts of data. We have reported suc-cesses in each aspect of the combinatorial process,most notably development of a method of imagingpolymer adhesion for a polymeric library. Not only hasit been demonstrated that the combinatorial approachcan greatly reduce measurement time, but we have alsoobserved new phenomena in several experimental sys-tems including the structure of thin films of block co-polymers.

• The Polymers Division has a sustained effort in develop-ing methods to measure polymer properties during theirprocessing. The initial application was in measurementof temperature in the resin, rather than in the process-ing equipment as is traditionally done. This workshowed that the resin temperature was frequently muchhigher than that given by the traditional temperaturemethod. This sensor work has been extended to mea-surement of polymer orientation that is of particularinterest in film blowing. Other optical methods havebeen developed to elucidate the origins of “sharkskin”surface imperfections in extrusion of polyolefins. Withthese tools better control of polymer processing andstrategies to improve end products are made possible.

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• The Division’s work toestablish matrix-as-sisted laser desorp-tion/ionization massspectrometry (MALDIMS) as a quantitativetool for syntheticpolymers advancedthis year with thesuccessful completionof an inter-laboratorycomparison with 23institutions. For thefirst time, NIST hasprovided the MALDIMS of polystyreneStandard ReferenceMaterial 2888. Of par-ticular significance, wehave overcome theineffectiveness ofconventional methodsof cationization ofpolyolefins and dem-onstrated the massspectroscopy of poly-ethylene by a covalentcationization method.Although this polymertype dominates thesynthetic polymermarket, determinationof their molecular mass and molecular mass distributionhas been difficult and not quantitative.

In looking forward to next year, several significant ad-vances can be anticipated. Our pioneering work demon-strating high throughput experimental methods will begiven a new home in an extensively remodeled laboratoryand with the initiation of an industrial consortium, theNIST Combinatorial Methods Center. Another laboratoryremodel will provide facilities to initiate a new program inmetrology for tissue engineering that includes collabora-tions with the NIST Biotechnology Division and twoinstitutes at the National Institutes of Health. Both ofthese projects have received support from the NIST com-petence building program after success in the 2000 and

2001 competitions. Inpolymer processing wewill focus on new mea-surement technologythat will provide theability to control extru-sion instabilities ofsharkskin and grossmelt fracture. In themicroelectronics area weare working to developan extension of ourporous thin films mea-surement method thatcan be implemented inthe industrial laboratorywithout the need foraccess to our special-ized neutron and x-rayfacilities.

Among the principaloutputs of the Divisionare technical publica-tions; the number ofpapers published is thehighest among all NISTDivisions. Every year inour annual report weprovide a list of publica-tions for the past year.The Division also is-

sues a CDROM of its publications for each calendar year.To provide more timely access to our technical publica-tions, the publications are also being organized for distri-bution on the Division web site. The collection is orga-nized by research group, keywords from the papers, anda set of subject terms that correspond to current thrustsin polymer science and technology. The most recent ver-sion of the Polymers Division web site is available athttp://www.nist.gov/polymers.

The first year of the 21st century has been an excellentone for the Polymers Division as we have also enjoyed thecelebration of the NIST Centennial. I hope this annualreport provides a useful overview of our activities. We arealways pleased to provide more details. Feel free to con-tact us for more information.

Eric J. AmisChief

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The following Technical Highlights section includes ex-panded descriptions of research projects that have broadapplicability and impact. These projects generally con-tinue for several years. The results are the product of theefforts of several individuals. The Technical Highlightsinclude:

• Mass Spectrometry of Polyethylene by the “CovalentCationization Method”

• Combinatorial Study of Surface Pattern Formation inThin Block Copolymer Films

• Measurement Methods Aid Development of Photo-resists for Next-Generation Photolithography

• Polymer Mass Distribution by Mass Spectrometry

• Multi-Fiber Failure Propagation

• Biocompatibility of a Moldable, Resorbable, CompositeBone Graft

• The Mechanism of Sharkskin


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Polyolefins dominate the synthetic polymer market. Whilethey have a very long production history, new develop-ments in metallocene catalysts have caused a great resur-gence of activity resulting in a wide variety of new appli-cations and increased material production. The newcatalysts can provide unprecedented control of polymermolecular mass and molecular mass distribution, copoly-merization control, stereochemistry, etc. Molecular massdistributions of polyolefins currently are determined bygel permeation chromatography, a method that requirescalibrations by mass standards. Such standards do notexist for these new types of polyolefins, thus crude ap-proximations are used that introduce large uncertainties.MALDI has provided valuable information on the natureof the polymerization process and the resultant structurefor many other polymer types, but not for polyolefins. Ifpolyolefins could be routinely analyzed by MALDI, devel-opment time for new catalysts and polymers could begreatly reduced.

Synthetic polymer cationization by metals such as sodium,potassium, silver, copper, etc., involves association ofcations with functional groups on the polymer. Examplesof functional groups include the carbonyl groups of meth-acrylate polymers, the double bonds of diene polymers,and the phenyl groups of styrenics. Polymers that lackpolar, unsaturated, or aromatic groups cannot be analyzedby MALDI. Thus, polyolefins (polyethylene, polypropy-lene, polyisobutylene, poly(methyl pentene), etc.) areexcluded.

A chemical modification method has been developed inthe Polymers Division that allows mass spectrometry to beperformed on these materials for the first time. Two syn-thetic steps are involved: bromination of the polymer,followed by conversion of the brominated site to acharged ammonium or phosphonium group. Here we giveresults for a low mass fraction of a commercial polyethyl-ene: NIST Standard Reference Material, SRM 2885. Thebromination reaction employed brominates sites ofcarbon-carbon double bonds, present in low concentra-tion in many commercial polyethylenes. The content ofcarbon-carbon double bonds of structure RCH=CH

2 (vi-

nyl) of SRM 2885 is determined from Fourier-transforminfrared spectroscopy. The determined value, (0.125 ± 0.01)

Mass Spectrometry of Polyethyleneby the “Covalent Cationization Method”

Saturated hydrocarbon polymers, polyethylene and polypropylene, are the most widely used of all synthetic polymers.Their molecular mass and molecular-mass distribution (MMD) are critical in determining processing and performanceproperties. Mass spectrometry is currently the most promising method for obtaining accurate absolute MMDs; however,polyethylene and other polyolefins have not been amenable to mass spectrometric characterization due to the ineffec-tiveness of conventional methods of cationization. A new method has been developed in which an organic cation iscovalently bonded to the polymer to produce the necessary ionization for successful matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS).

C=C per 100 C, corresponds to approximately one vinylgroup for every 2 molecules as estimated from the certifiedmass average molecular mass of 6280 g mol-1 and a poly-dispersity of 1.13. The vinyl content is reduced by bromi-nation to 0.32 ± .03 of its original value. Next, the bromi-nated polymer is treat with tri-phenyl phosphonium (TPP).Using integrated intensities from alkyl benzenes the phe-nyl content in TPP-treated polyethylene is estimated to be0.27 phenyl/100 C, or 2 per original vinyl group, approxi-

mately. Since each phosphonium group contains 3phenyls and the reaction yields one phosphonium groupper reacted vinyl the qualitative results are in agreementwith the observation that approximately one-third of theoriginal vinyl groups remain unreacted by the treatmentemployed here. Hence, an estimated one-third of the origi-nal polyethylene molecules are labeled with TPP by thechemistry employed.

The figure above shows the MALDI-TOF-MS resultsfrom SRM 2885 that has been modified by the covalentcationization method. No smoothing or baseline subtrac-tion was used in the data presented. A strong MALDIsignal was produced from the modified polymer while the


For More InformationOn This Topic:

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unmodified and the brominated polymer produced nosignal at all. Oligomers are clearly present up to 7000g mol-1, higher than ever observed before for intact,saturated-hydrocarbon oligomers by mass spectrometry.Current work centers on extending the mass range tohigher values more representative of commercial polymers.The mass spectrum of SRM 2885 shows a strong repeatingpattern of 28 g mol-1; however, a pronounced repeat of14 g mol-1 is also apparent. This may be due to fragmenta-tion of the polymer in the mass spectrometer or may be aconsequence of the polymerization chemistry of olefins.The abundance of tightly spaced peaks with 14 g mol-1

spacing below 3000 g mol-1 suggests the existence offragmentation. However, these peaks also exist at the veryhigh mass end of the spectrum above 6000 g mol-1. It isknown that premature chain termination can producemolecules with an odd number of carbon atoms and thus

W.E. Wallace, B.J. Bauer (Polymers Division, NIST)

Bauer, B.J., Wallace, W.E., Fanconi, B.M., Guttman, C.M. “Covalent CationizationMethod” for the Analysis of Polyethylene by Mass Spectrometry. Polymer 42,9949–9953 (2001).

can give a repeat spacing of 14 mol-1. It is possible thatboth of these two effects may be occurring in this massspectrum.

While simple modification of as-polymerized polyolefinswith bromine and TPP represents a model case, the cova-lent cationization method applies to other chemistries andpolymer types as well. Many other types of chemistryother than functionalizing vinyl groups are possible. Forexample, hydroxy-terminated polystyrene, polybutadiene,and hydrogenated polybutadiene (fau polyolefin) havebeen modified by converting the hydroxy to bromide bytreatment with PBr

3 and then converting to –N+(CH

3)

3 or

–P+(C6H

5)

3 by treatment with trimethyl amine and TPP

respectively. The figure on the left shows a hydroxy-terminated hydrogenated polybutadiene covalentlycationized with tri-methyl ammonium. The spectrum showsexcellent resolution and low background making it ideal todetermine molecular-mass distribution. Conventional metalcationization methods fail for this material even thoughoxygen is present in the end group because the oxygen isin such low abundance that metal cationization becomes avery unlikely event. Covalent cationization overcomes thisby chemically adding a charge to each chain.

Industry Interaction:

Efforts to expand the MALDI technique to nonpolarpolyolefins are in progress. Major product monitoringcost- and time-savings should accrue to industrialpolyolefin suppliers and users with this technique whenperfected.

Board on Assessment of NIST Programs, NationalResearch Council


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Combinatorial Study of Surface Pattern Formationin Thin Block Copolymer Films

Figure 1. True color optical micrographs of a PS-b-PMMAfilm having a gradient in thickness from 63 nm to 117 nm.The addition of three successive lamellae to the surface isshown.

Block copolymers are amphiphilic polymer materials com-posed of two different polymers joined by a covalent bond.This linkage of chemical functionality inhibits phase sepa-ration of the polymers beyond a molecular scale and makesthese materials useful as stable elastomers, adhesives, andas surfactants stabilizing polymer blends against phase-separation. The tendency of block copolymers to self-organize into ordered nanoscale patterns in bulk and in thinfilms has also led to recent intense interest in using thesematerials as templates for nanoscale arrays in thin films andphotonic devices. Block copolymer films exhibit seeminglystable surface patterns over large-length scales (tens of

micrometers) whose origins are not understood, butwhich provide an attractive methodology for formingsurface patterns of tunable dimension. We determine, bycombinatorial high-throughput approach, the range ofmorphology types that arise through self-organization inthese films and the factors that influence their size andstability. The high information content generated by thecombinatorial (“combi”) method revealed surface patterntypes overlooked in the past and the phenomenologygoverning the size of these patterns. The combi results onself-organization in such systems should be helpful tounderstand the physical origin in terms of competitionbetween micro phase-separation and surface elasticity,and the fundamental nature of molecular interactionsbetween the components of the block copolymer and withsurfaces.

Previous studies of surface pattern formation in blockcopolymer films have not yielded a predictive theory thatquantitatively relates the phenomena to molecular param-

eters. Among questions about basic phenomenology,factors governing the size of the island and hole patterns(e.g., molecular mass M and temperature T) in these filmsare not well understood. Notably, the size of these patternsis often large in comparison to the lamellar spacing L

o (or

even film thickness h) so that the molecular interpretationof these patterns is subtler than ordering in bulk blockcopolymer materials. The precise thickness range in whichthe films remain smooth is another basic film property thatrequires further investigation. Since these film propertiesare crucial for the development of a theoretical descriptionrelating the self-organizing process to fundamental mo-

Unique properties of block copolymers in melts, blends and solutions lead to their use as adhesives, emulsifying agents,thermoplastic elastomers, compatibilizers, etc. Many applications exploit the ability of these materials to self-organizeinto ordered structures in bulk and in thin films. The nature of interactions in block copolymer systems is determined byexploiting the ability of block copolymers to form quantized periodic structures in thin films that directly reflect molecu-lar parameters such as block lengths, chemical interactions between block constituents, and interactions with inorganicsubstrates. Combinatorial gradient methods are used to validate a vast body of existing literature and simultaneouslydiscover new knowledge reflecting the influence of different molecular parameters on entropic, enthalpic and kineticrelationships in block copolymers.

lecular interactions in the system, we have investigatedpattern formation in block copolymer films using combina-torial methods on films produced by a flow-gradient tech-nique to have a range of h and M.

Near symmetric poly(styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers with different M were used toprepare thickness gradients on Si wafers. The wafer wasattached to a robotic stage and a small amount of solutionspread under a suspended knife-edge at constant accelera-tion to form a thickness gradient. Film thickness was mea-sured using an automated UV-visible interferometer. For thecurrent experiments, up to four PS-b-PMMA gradient filmswere placed on the same wafer and annealed at 170 °C un-der vacuum to allow ordering of the block copolymers.Optical microscopy and atomic force microscopy (AFM)were used to characterize the surface patterns. Previousstudies showed that when PS-b-PMMA is cast and an-nealed on a Si substrate the PMMA preferentially segre-gates to the substrate while the PS segregates to the airinterface. The limited data in literature from individual(single-thickness, single molecular mass) film studies sug-gests that this behavior produces smooth films for thick-



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P.A. Smith, J.F. Douglas, E.J. Amis, A. Karim (Polymers Division, NIST)

Smith A.P., Douglas, J.F., Meredith, J.C., Amis, E.J., Karim A. Combinatorial Studyof Surface Pattern Formation in Thin Block Copolymer Films, Phys. Rev. Lett., 87,015503, (2001).

Smith A.P., Douglas, J.F., Meredith, J.C., Amis, E.J., Karim A. High-ThroughputCharacterization of Pattern Formation in Symmetric Diblock Copolymer Films.J. Poly. Sci. Polym. Phys. 39, 2141 (2001).

Figure 2. AFM micrographs (white corresponds to highertopography) of a PS-b-PMMA gradient film at differentthicknesses showing: (a) the smooth morphology; (b andc) islands; (d) labyrinthine pattern; and (e and f) holes onthe surface of the films.

ness ranges near the characteristic values that are half-integer multiples of lamellar spacing, L

o, while hole and

island patterns form when the film thickness deviates sub-stantially from the characteristic values.

An example of the morphological change in the block co-polymer films as a function of h is shown in Figure 1. Thisimage shows optical micrographs of a 26k PS-b-PMMA(Lo = 17 nm) continuous gradient film with a thickness rangeof » 54 nm corresponding to the addition of three lamellaelayers. The morphology evolves from smooth to islands tolabyrinthine to holes to smooth as the film thickness in-creases. The regions of hole and island pattern formationare consistent with previous observations on films of fixedthickness, but the observation of the broad smooth regionsand the labyrinthine morphology are novel. Figure 2 showsAFM micrographs of the surface patterns at higher magnifi-cation. The film is smooth for the thinnest film, with islandsforming as h increases that coalesce into a labyrinthinepattern. For even greater h a continuous lamella with holeforms. These morphological trends are observed for all Mand thickness range up to 6.5 L

o. The importance and impli-

cations of the novel observations are discussed below.

The observation of the broad smooth regions implies achange in film thickness across this area where the blockchains of styrene and methyl methacrylate can stretch up to

a maximum of 14 percent with increase of film thickness, orcontract down to a minimum of 14 percent with decrease offilm thickness, without forming additional layers. Thesemaximum and minimum limits of extensibility are novelresults that will be useful in developing a theoretical un-derstanding of the relative importance of entropic (chainstretching) versus enthalpic (chemical interaction param-eter) factors in block copolymers. The results on limits ofextensibility are also found to be nearly invariant withmolecular mass thus generalizing the phenomena. Nostatistically significant variation in this value was foundwith increasing h up to the maximum of » 6.5 L

o tested,

indicating that height variation is confined to the outer-most lamella that is another novel observation. We at-tribute the height variation resulting from chain deforma-tion in the outermost surface lamella to the kinetics of theordering process.

The kinetics of the self-organization process can be mea-sured by the continuous gradient approach as well, asdemonstrated for the structural evolution of the novellabyrinthine regime. This was obtained by measuring thedependence of the pattern size on M at different times.The scale (1) of the patterns decreases with an increase inM (a non-intuitive result), yielding the relationship λ (mm)~ M-1.65. This behavior is attributed to the increasing sur-face elasticity of the block copolymers with increasing Mthat serves to inhibit formation of large surface features.

In summary, combinatorial methods have been success-fully applied to observe novel morphologies and to estab-lish fundamental kinetic relationships in the ordering prop-erties of block copolymer films. These results agree wellwith existing non-combinatorial literature data on the samesystems, validating the combinatorial approach and thecontinuous gradient method. The results will enable de-veloping a theoretical understanding of key questions inblock copolymers such as the nature of interactions be-tween blocks, as well as block interactions with differentmaterials. The investigative combinatorial tools and meth-odologies developed will accelerate research in practicalapplication areas of block copolymers such ascompatibilization, adhesives, etc., in the future through thedevelopment of a NIST Combinatorial Methods Center.

“This…is an excellent example of using a clever (combi-natorial) trick to extract new and important insightsfrom what even the authors admit is a well-studied sys-tem. Well done!”—Physical Review Letters ManuscriptReview


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Measurement Methods Aid Development ofPhotoresists for Next-Generation Photolithography

Photolithography, the process used to fabricate integrated circuits, is the key enabler and driver for the semiconductorindustry. As lithographic feature sizes decrease to the sub-100-nm length scale, significant challenges arise because thefeature size is reaching the limits of current structural characterization methods. In addition, both the image resolutionand the thicknesses of the imaging layer approach the inherent macromolecular dimensions characteristic of the poly-mers used in the photoresist film. Unique high-spatial resolution measurements are developed to understand the mate-rials and processes challenges facing the development of photoresists for next-generation sub-100-nm lithography.

Photolithography

Photolithography remains the drivingtechnology in the semiconductor industryto fabricate integrated circuits with everdecreasing feature sizes. There are signifi-cant challenges in extending this technol-ogy to fabricate the smaller feature sizes(sub-100 nm) needed to continue perfor-mance increases in integrated circuits. Tosucceed, the critical dimensions (CD) ofthe lithographic structures must be con-trolled to within 10 nm. An increasinglydifficult challenge lies in measuring struc-tural parameters (feature size, shape andquality) over these length scales. Further,new radiation sources with shorter wave-lengths (193 nm and 157 nm) require photoresist films lessthan 100-nm thick to ensure optical transparency anduniform illumination. In these ultrathin films, confinementcan induce deviations in several key materials parameterssuch as the macromolecular conformation, glass transitiontemperature, viscosity or transport properties. It is not yetclear how deviations due to confinement will affect theultimate resolution in these ultra-thin photoresist films.

To advance this key technology, we work closely withindustrial partners including IBM, Shipley and BrewerScience to develop unique high-spatial resolution mea-surements to better understand the lithographic process,to guide the development of materials, and to providehigh-quality data for key model photoresist systemsneeded in advanced simulation packages. We have madesignificant advances in two areas, a new method for thestructural characterization of lithographically preparedstructures and the first measurements of the atomic-leveldynamics of polymers in ultrathin films.

Structural Metrology with SANS

As feature sizes continue to decrease with dimensionsapproaching 100 nm, the allowable resolution limits of thelithographic process become more stringent and difficultto measure. The precise measurement of the size and qual-ity of lithographically prepared features as they decreasein size is critical for evaluating and improving new litho-graphic processes and materials. Current microscopy-

based techniques such as scanningelectron microscopy (SEM) and atomicforce microscopy often require special-ized modifications to enable the mea-surement of either the critical dimensionor feature resolution parameters. Moreimportantly these techniques becomeextremely challenging as feature sizescontinue to decrease.

We have demonstrated the powerful useof small-angle neutron scattering (SANS) to quickly, non-destructively, and quantitatively characterize both the sizeand profile of lithographically prepared structures as pre-pared on a silicon wafer substrate. Until recently, SANSinstruments were unable to measure lithographic featuresizes (sizes greater than 300 nm) and neutron beam fluxeswere insufficient to measure scattering from thin-filmstructures. Today, the high-intensity NIST Center forNeutron Research (NCNR) neutron source, new focusingoptics, and smaller lithographic features allow for theSANS measurements. Other important advantages include:a) the measurement of structures on silicon because singlecrystal silicon wafers are transparent to neutrons; b) ameasurement metric averaged over an area of several cm2;c) less stringent SANS instrument requirements as litho-graphic structures decrease in size; and d) no need for acalibration standard.

We have demonstrated the SANS metrology through ananalysis of the scattered intensity from a periodic gratingstructure (figure above) with a nominal linewidth of150 nm. In the SANS data, up to six orders of diffractionpeaks are observed. The position and intensity of thesepeaks provide measures of CD and the cross-sectionalshape with nanometer resolution. SANS measurementsmay serve as a powerful tool to validate calibration stan-dards and is one of very few methods able to providehigh-resolution metrology for the evaluation of new mate-rials and processes for structural features expected to besmaller than 100 nm in size.

Figure 1. Top-down and edge-on SEMimages and two-dimensional SANS datafrom several periodic grating patternswith 150-nm linewidths.



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Local Polymer Dynamics

Current photoresists use a photogenerated acid catalyzeddeprotection reaction on the polymer to produce a solubil-ity change in exposed areas. The local, atomic-level, dy-namics of the photoresist polymer directly affect transportprocesses essential to modern photoresists, such as thediffusion of photogenerated acids and other small mol-ecules within the polymer matrix. To date, changes in thelocal dynamics of polymer thin films have been inferredfrom changes in macroscopic quantities such as the appar-ent glass transition temperature, Tg, as a function of filmthickness and substrate interaction energies. Direct mea-surements of the segmental motions of polymer chainsconfined to ultrathin films will provide a molecular pictureof observed changes in these macroscopic quantities andinsight into differences in photoresist transport processesin ultrathin films. By using different polymers and poly-mer/substrate combinations, we obtain crucial insight intothe dynamical effects of polymer thin-film confinement.

E.K. Lin, C.L. Soles, W.L. Wu (Polymers Division, NIST)

Wu, W.L., Lin, E.K., Lin, Q.H., Angelopoulos, M. “Small Angle Neutron ScatteringMeasurements of Nanoscale Lithographic Features,” J. Appl. Phys., 88, 7298 (2000).

Soles, C.L., Lin, E.K., Lenhart, J.L., Jones, R.L., Wu, W.L., Goldfarb, D.L., Lin, Q.,Angelopoulos, M. “The Effects of Thin-Film Confinement on the Thermal Propertiesof Typical Deep-UV Photoresist Resins,” submitted to J. Vac. Sci. Tech. B. (2001).

Incoherent neutron scattering at the NCNR High FluxBackscattering Spectrometer was used to directly probethe atomic and segmental motions of polymer films as thinas 75 Å on silicon substrates for the first time. This tech-nique characterizes motions on a frequency scale of200 MHz or faster in terms of a mean-square-displacement<u2>. We find that thin-film confinement generally dimin-ishes <u2>, irrespective of the polymer/substrate interac-tions. The degree to which <u2> is suppressed appears todepend on the level of vibrational anharmonicity in thepolymer. Strongly anharmonic polymers show larger de-creases in <u2>, particularly below the bulk Tg. For ex-ample, the protected (before exposure) photoresist poly-mer shows a high level of mobility (large <u2>) below theglass transition that is suppressed strongly by confine-ment. However, the deprotected version of this polymershows a much lower level of sub-Tg mobility (primarilyharmonic motions) with very little effect from confinement(Figure 2). The markedly different behavior between re-lated polymers provides important insight into the depen-dence of photoresist properties on the chemical structureof the polymer, information important to photoresistdesigners.

“The continuous miniaturization of semiconductor de-vices poses many challenges to lithography…One ofthese challenges is to measure precisely the size, shapeand quality of the circuit patterns. The SANS method is anew technique to measure lithographic patterns [and]capitalizes on the unique capabilities at NIST…”

Q. H. Lin—IBM T. J. Watson Research Center

“The gate CD [critical dimension] control requirementsfor the 130-nm node and below are also among the mostdifficult challenges [for lithography]. Advances in pro-cess control, resist materials, line edge roughness andmetrology will be necessary to achieve less than 10-nmCD control.”

1999 International Technology Roadmap forSemiconductors.

Figure 2. Mean-square displacement, <u2>, as a functionof temperature for a protected polymer (PBOCSt) and adeprotected polymer (PHS) for both the bulk material and10-nm films.


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Matrix-assisted laser desorption/ionization mass spec-trometry (MALDI MS) is a new method of polymer analy-sis that works well for biopolymers, proteins and nucleicacids, that are essentially of single mass (excluding isoto-pic effects). The situation is quite different with syntheticpolymers owing to the presence of a distribution ofmasses that not only spreads the signal over a range ofmasses corresponding to the polymer’s mass distribution,but also invokes questions of how the signal at the detec-tor is affected by having a distribution of masses. Aspreliminary to developing a research program that ad-dresses issues of how sample preparation, laser intensity,instrument parameters and detector response may beaffected by mass distribution, NIST organized and led aninter-laboratory comparison to determine the currentstatus of measurements and began a dialog on quanti-tative mass spectrometry of synthetic polymers.

The inter-laboratory comparison was designed in con-sultation with the American Society of Mass Spectrom-etry Working Group on Synthetic Polymers. Member-ship in this special interest group represents manyindustrial laboratories, including those of major produc-ers of synthetic polymers. Samples of well-characterized low-molecular mass polystyrene weresent to any institution requesting it.

The polystyrene was custom synthesized to specifica-tions provided by NIST to insure that the numberaverage molecular mass could be determined by high-resolution nuclear magnetic resonance (NMR) and themass average molecular mass by light scattering. Thesevalues by classical methods were used to comparemoments calculated from the MALDI mass spectrum.One end of each polystyrene molecule contained a t-butylgroup that was not only detectible by NMR but also wasuseful in assessing the quality of end group determina-tions by MALDI MS.

Polymer Mass Distribution by Mass SpectrometryMolecular mass distribution is the characteristic that most affects processing and properties of polymers. However, inabsence of absolute methods for measuring mass distribution, methods that require calibration must be used. Owing tothe lack of suitable calibration standards for most polymers, alternative methods of determining mass distribution aresought. Mass spectrometry is an absolute method for determining mass of molecules of essentially single mass. Withrecent advances the method may work for synthetic polymers, as well, provided that the signal strength depends onmass in a predictable manner. An inter-laboratory comparison of analysis of polystyrene by mass spectrometry has beencompleted with the objective of assessing the current status of the method and evaluation of how moments of the mea-sured mass distribution compare to those determined with classical methods.

A total of 23 institutions participated in the inter-labora-tory comparison (10 industrial, 9 academic and 4 govern-ment laboratories). NIST Polymers Division also character-ized the polymer by NMR for M

n and by light scattering

for Mw.

Fourier transform infrared spectroscopy confirmed thepresence of the t-butyl end group, as anticipated by thesynthesis method. Size exclusion chromatography wasused to insure vial-to-vial homogeneity in the samplesdistributed to participants. Each participating laboratorywas asked to perform MALDI mass spectrometry usingtwo distinct protocols, one prescribed and the other left tothe discretion of the participants.

Figure 1. Mass spectrum of polystyrene used ininterlaboratory comparison by MALDI MS.



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Participants were instructed to report their mass spectra aswell as moments of the mass distribution. The latter re-quest was used to assess the status of analysis software,which is largely provided by MALDI MS instrumentmanufacturers.

Analysis of the moments reported by the participantsrevealed inconsistencies among laboratories in calibratinginstruments. These inconsistencies also affected determi-nations of end group mass. By compiling all the reportedspectral data (as opposed to reported moments) usingboth protocols into one analysis it was found that MALDIToF MS returned an M

n of (6610 ± 100) g/mole and an M

wof (6740 ± 90) g/mole, uncertainties are standard uncertain-ties. These numbers were below those of the classicalmethods, but still within the overlapping uncertaintyranges. Detailed results of this study have been recentlypublished in Analytical Chemistry.

The polystyrene used in the inter-laboratory comparisonwill be available as Standard Reference Material (SRM)2888, certified for mass average molecular mass by lightscattering. The NMR determined number average massand the MALDI MS data, including the full mass spec-trum, will also be available as supplemental data. This isthe first polymer molecular mass standard to have its massdistribution presented. Although polystyrene calibrantsfor gel permeation chromatographs are readily available,this new polystyrene SRM demonstrates the potential ofMALDI MS for mass distribution measurements in syn-thetic polymers.

C.M. Guttman, B.M. Fanconi (Polymers Division)

Guttman, C.M., Wetzel, S.J., Blair, W.R., Fanconi, B.M., Girard, J.E., Goldschmidt,R.J., Wallace, W.E., VanderHart, D.L. NIST-Sponsored Interlaboratory Comparisonof Polystyrene Molecular Mass Distribution Obtained by Matrix-Assisted LaserDesorption/Ionization Time-of-Flight Mass Spectrometry: Statistical Analysis.Analytical Chemistry, 2001, 73, 1252-1262.

The establishment of a standard method for determinationof mass distribution by MALDI MS will facilitate its ac-ceptance as a new method. Owing to the importance ofmass measurements within the polymer industry, analyticallaboratories that serve the industry and research laborato-ries in general, an effort was initiated to develop a stan-dard measurement protocol for mass measurements byMALDI MS. A new technical working activity, TWA 28,was formed under the auspices of VAMAS, the VersaillesProject on Advanced Materials and Standards. Laborato-ries in five countries, Canada, Italy, Germany, Japan andthe United States are engaged in developing a measure-ment protocol for analysis of the mass distribution ofpolystyrene by mass spectrometry. The framework of theproposed measurement method will be the sample prepara-tion and measurement outline used in the inter-laboratorycomparison augmented to reflect knowledge gained in theanalysis of the inter-laboratory comparison. Although themeasurement uncertainty of the inter-laboratory compari-son was much less than common with classical methodsno estimate could be made of systematic uncertainties,type B.

An assessment will be made of possible sources of sys-tematic uncertainty. Collaborative research will be under-taken to reduce sources of uncertainty, where possible.

“NIST develops standards for MS of polymers...importantbecause mass distribution of synthetic polymers affectsprocessing and properties.”

C & E News 6/11/2001


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The implementation of advanced materials in structuralapplications is often hampered by the inability of thedesign engineer to predict reliably failure behavior, failurestrength, fatigue behavior, energy absorption characteris-tics, and mechanical response of the composite partto multi-axial loading conditions. Because of their complexarchitecture, composites areanalyzed on many differentscales, with micro-mechanicsand macro-mechanics beingtwo broad classes. Micro-mechanics provides informationabout non-averaged localizedproperties (e.g., constituentdeformation and stresses andlocalized failure behavior—fiber, matrix and interphase).Qualitatively these localizedproperties have been shown tostrongly influence the perfor-mance properties of the com-posite. In contrast, macro-mechanics analyses, which are used at the lamina leveland higher, use average strength and stiffness propertiesand failure criteria defined by average stresses and overalllamina strengths. Although the latter approach iscomputationally expedient, it fails to predict the effect ofmicrostructure changes on composite failure behavior.

The goal of our work is to provide the necessary linksbetween macro-mechanics approaches and micro-mechanics properties. For reliable prediction of compositeperformance properties, non-averaged micro-mechanicsproperties that account for the composite environmentmust be included, while keeping the computational pro-cess tractable. The microstructure of the composite laminais being used to guide the selection of appropriate micro-mechanics experiments and analysis techniques to obtainmicro-mechanics parameters. Initially, we use 2-D multi-fiber arrays in experiments to quantify the interactionbetween fibers during fiber fracture, constituent deforma-tion behavior in the composite environment, and the local-ized failure behavior of the fiber, matrix and interphaseregion.

Multi-Fiber Failure PropagationWith the increasing use of advanced composites in structural applications, understanding how to predict and managefailure in composite structures has become a critical problem. As noted by the Automotive Composite Consortium, thereis a major need to generate relevant materials property data that can be used in a computational program by designengineers to predict composite performance. In response to this need, test methodologies and a tow-based modelingprogram are being developed to facilitate the seamless integration of critical materials data into composite analyses.

Results are shown in Figures 1 and 2, where fiber fractureswith debonding and associated matrix crack formation areillustrated for a 2-D multi-fiber array composed of E-glassfibers embedded in diglycidyl ether of bisphenol-A(DGEBA) epoxy resin cured with meta-phenylene diamine(m-PDA). Although the interfiber spacing, φ, is less than

Figure 1. Fiber break patterns from E-glass/DGEBA/m-PDA 2-D multi-fiber array immediately after removingstress. The interfiber spacing is denoted by φφφφφ.

Figure 2. Fiber break patterns from E-glass/DGEBA/m-PDA 2-D multi-fiber array 24 h after removing stress.The interfiber spacing is denoted by φ φ φ φ φ.



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mation. Although the origin of these deformation regionsare not clearly understood, 45-degree deformation bandsemanating from the matrix cracks during the test undertensile conditions have been observed.

Using the same constituent composition, fiber fracture in amulti-fiber specimen with the fibers touching is shown inFigure 3. In this specimen, matrix crack formation has beensuppressed, and clustering of the non-aligned fiber breaksis observed. The extensive matrix damage around the fiberbreaks occurred when the applied stress on the specimenwas removed. However, the absence of this type of defor-mation in the non-touching 2-D array (Figure 3), suggeststhat the matrix deformation is higher surrounding the fiberbreaks in the touching fiber specimen. In addition, thismatrix damage along with the location of each fiber breakhas been observed by optical coherence tomography(OCT).

Capitalizing on the ability of OCT to see changes in thedeformation state in the resin, residual stresses have beenobserved in 2-D multi-fiber specimens. These stresses mayinfluence the observed failure behavior.

In previous research on single-fiber specimens we havenoted that the matrix is non-linear viscoelastic. However,reconciling this effect with the occurrence of brittle frac-ture in composite specimens has been problematic. A 2-Dmulti-fiber array specimen was taken in several steps to astrain level that induces fiber fracture. During a period of

5 min, numerous non-aligned fiber breaks occurin the observation region,reflecting the role that thematrix has on the stressredistribution process inadjacent fibers after fiberfracture (See video atwebsite: http://polymers.msel.nist.gov/researcharea/multiphase/project-detail.cfm?P2D=56.). Atthe end of this period thespecimen fails in a brittlemanner away from the

observation region. This video indicates that the nucle-ation of the critical flaw that induces brittle compositefailure may be time dependent and controlled by theviscoelastic matrix and the mode of interphase failure thataccompanies fiber fracture.

“…understanding how to manage the dissipation ofenergy in composite structures during crash conditionshas become critical problem. The goal is to meet or ex-ceed the standard that has been set by steel.”

Nancy L. JohnsonDirector for Focal Project 3–ACCVehicle Analysis and Dynamics Lab–GM

“Although DOE and others are doing crash energy man-agement modeling, computational models that accu-rately predict energy dissipation during crash scenariosare still lacking.”

Raymond G. Boeman, Ph.D.Automotive Composites SpecialistsOak Ridge National Laboratory

four fiber diameters in the array, the fiber breaks in adja-cent fibers are not aligned vertically as predicted bytheory. Computational predictions indicate that the stressoverload in adjacent fibers is smaller for non-alignedbreaks. Hence, the composite toughness is predicted tobe higher. The mechanism(s) that generates the non-alignment of fiber breaks, however, is not well understood.The change in contrast between Figure 1 and Figure 2visually represents the stress relaxation in the viscoelasticmatrix after a period of 24 h. The persistent hue after 24 hbetween fiber breaks in adjacent fibers is permanent defor-

Figure 3. Fiber break patterns and matrix deformation inE-glass/DGEBA/m-PDA 2-D multi-fiber array (un-stressed and fibers touching).

G.A. Holmes, W.G. McDonough, C.C. Han (Polymers Division, NIST)

See website: http://polymers.msel.nist.gov/researcharea/multiphase/project-detail.cfm?PID=56


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Over 100,000 bone grafts are performed each year in theUnited States, but the amount of available autologousbone is limited and available material is difficult to shape.Thus, the development of a synthetic, moldable bone graftmaterial is a primary goal of the tissue engineering indus-try. A self-setting calcium phosphate cement (CPC) thatcan be sculpted to fit the contours of a wound and con-sists of dicalcium phosphate and tetracalcium phosphatewas designed by co-workers from the American DentalAssociation Health Foundation at NIST. We sought toimprove this cement by making it macroporous andosteoinductive through inclusion of polymer microspheresand a bone growth factor, respectively.

We have assessed the biocompatibility of themacroporous composite bone graft (CPC polymer) consist-ing of self-setting calcium phosphate cement and biode-gradable polymer microspheres (175 µm–355 µm diameter)using cell culture techniques. CPC powder was mixed withpolymer microspheres and water to yield a workable paste.The cement then hardens into a matrix of hydroxyapatitemicrocrystals containing polymer microspheres. The ratio-nale for this design is that the microspheres will stabilize

Biocompatibility of a Moldable,Resorbable, Composite Bone Graft

The blessing of living longer is accompanied by the burden of aging. There is an overall risk of fractures of the hip,spine and distal forearm that will afflict 40 percent of women and 13 percent of men 50 years of age and older. Restor-ing form and function to bone defects in an elderly, osteoporotic population of more than 52 million Americans, overthe age of 65 by the year 2020, will be a daunting challenge. To meet this challenge, scientists from the Polymers Divi-sion and the American Dental Association Health Foundation have used polymers, calcium phosphates and growthfactors to develop a biodegradable composite bone graft for bone regeneration. The composite bone graft was found tobe biocompatible and to release at a controlled rate a growth factor that stimulates bone regeneration.

initially the graft, but then can gradually degrade, func-tioning as a ‘polymer porogen’ to leave behindmacropores for colonization by osteoblasts. The CPCmatrix then potentially could be resorbed and replacedwith new bone.

In the present work, osteoblast-like cells (MC3T3-E1 cells)were seeded onto control CPC (CPC cement only, withoutpolymer microspheres) or CPC-polymer specimens andevaluated with fluorescence microscopy (live-dead stain),scanning electron microscopy (SEM), environmental scan-ning electron microscopy (ESEM) and the Wst-1 assay (acolorimetric, enzymatic assay for mitochondrial dehydro-genase activity). Examples of data are shown in Figures 1–3. Cells were able to adhere, attain a normal morphology,proliferate, and remain viable when cultured on the newcomposite graft (CPC-polymer) or on the control graft(CPC alone). These results suggest that our new cementconsisting of CPC and polymer microspheres isbiocompatible. This is first time that a ‘polymer-in-mineral’(polymer microspheres dispersed in a CPC matrix) cementhas been formulated that is moldable, resorbable and thatcan form macropores after the cement has set.

Figure 1 (left): SEM of the interior of CPC without polymer microspheres (left half) or with polymer microspheres (righthalf). The specimens were aged for 3 months in cell media to allow complete degradation of the polymer microspheres.Macropores (175 µµµµµm–355 µµµµµm in diameter) formed by the degradation of the polymer microspheres are visible in theright half panel. The inset is a larger view of the entire CPC-polymer specimen (6 mm in diameter by 4.5 mm in height).Figure 2 (right): SEM of cells cultured overnight on a CPC specimen which shows that cells can adhere and maintain anormal morphology when cultured on the cement. “Cell” indicates the cells and “CPC” indicates the cement.



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Additionally, we have improved the CPC by providingcontrolled release of an osteoinductive protein,transforming growth factor-β1 (TGF-β1). Initial releasestudies using a model protein (fluorescein-labeled ProteinA) showed that protein release kinetics could bemodulated by adjusting the amount of a porogen(mannitol) included in the CPC (Figure 4). More recentstudies have used TGF-β1 (Figure 5) in a composite ofCPC with salicylic acid as the porogen. In addition,release kinetics have been studied in CPC-containingbiodegradable polymers as porogens, similar to the CPC-polymer described above. These studies have shown thatrelease kinetics can be governed not only by the volumefraction of the porogen, but also by the composition ofthe porogen included in the cement (mannitol, salicylicacid or degradable polymer). These data have garneredinterest from several biotechnology companies that focuson the development of bone grafts.

The “polymer-in-mineral formulation is what separates”this cement “from the prior mineral-in-polymer formula-tions”—Reviewer for Journal of OrthopaedicResearch

Figure 3: Wst-1 assay for cells cultured 2 weeks onCPC and CPC-polymer specimens. The enzyme reactionwas quantitated by measuring the absorbance (450 nm) ofthe reaction wells and shows that the amount of dehydro-genase activity (which is proportional to cell number)present on CPC specimens is statistically the same asthat found on specimens of CPC and polymermicrospheres (CPC-polymer).

Figure 4: Release of fluorescein-labeled Protein A intophosphate-buffered saline at 37 o C from CPC/mannitolcomposite containing varying volume % of mannitol.

Figure 5: Release of TGF-βββββ1 into phosphate-bufferedsaline at 37 o C from CPC/salicylic acid composite.

F.W. Wang, C.G. Simon, Jr., C.A. Khatri (Polymers Division, NIST)

Wang F.W., Khatri C.A., Hsii J.F., Hirayama S., Takagi S. (2001) Polymer-filled cal-cium phosphate cement: mechanical properties and protein release. J. Dent. Res.80:591.

Simon, Jr., C.G., Khatri C.A., Wight S.A., Wang F.W. (2001) Preliminary Report onthe Biocompatibility of a Moldable, Resorbable, Composite Bone Graft Consistingof Calcium Phosphate Cement and Poly(lactide-co-glycolide) Microspheres.J. Orthoped. Res., submitted.


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Over the past 50 years, there has been sustained interestin the understanding and control of instabilities that occurupon pressure driven extrusion of molten polymers. Theseinstabilities limit the manufacturing rate and the materialsselection in continuous forming operations, such as sheetextrusion. Processors are forced to sacrifice final mechani-cal properties to achieve greater processability. From thescientific point of view, the understanding of these insta-bilities is challenging; despite much progress, fundamentalissues remain unresolved. An understanding of the causeof sharkskin would enable a more rational design of materi-als in order to eliminate it.

In this work we focus on the sharkskin instability. Thedriving force behind the attempts to understand sharkskinis that linear polyethylene of narrow molecular mass distri-bution particularly is susceptible to this instability. As thisinstability occurs at relatively low-extrusion rates, it istroublesome. The subject has received renewed attentionbecause newer metallocene-based polyethylene offeradvantages in mechanical properties, but often suffer fromthis extrusion instability. There have been numerous sug-gestions for the mechanism of sharkskin and for an eluci-dation of the conditions that produce it.

In 1977 it was suggested that sharkskin is caused by atearing of the polymer at the exit lip due to the high exten-sional flow forces generated at this point. Under theseconditions, the extensional stress exceeds the cohesivestrength of the molten polymer. In an alternative picture,the material undergoes cavitation just inside the tube,causing sharkskin. Others have suggested that sharkskinis due to an unstable flow boundary condition that oscil-lates between stick and slip. These models (and severalothers not mentioned for reasons of space) all make spe-cific predictions about the nature of the polymer flow field.Of particular relevance is the question of whether or notthe polymer sticks to the wall during sharkskin, or if itslips.

The aim of these experiments is to distinguish among thevarious possibilities described above. Many of thesemodels can be tested through a combination of micro-velocimetry, optical imaging, and surface modificationthrough fluoropolymer additives. We further conductexperiments under conditions of maximum industrial

The Mechanism of SharkskinThe rate limiting step in the manufacture of several important classes of polymeric materials is an extrusion instabilityknown as “sharkskin” in which the manufactured plastic has a rough surface containing a repeated pattern of ridges.This roughness causes a loss of clarity and a loss of ability to control final part size. Studied since the second worldwar, the cause of sharkskin remains an unsolved problem. Here we use the NIST Extrusion Visualization Facility tocapture the step-by-step kinetics of this extrusion instability. We are thus able to determine which of the proposedcauses of sharkskin is actually responsible.

Figure 1: As the extrusion rate increases, the final prod-uct becomes progressively distorted. (A) through (D) areknown as sharkskin and (E) is known as gross meltfracture.

In the case of extrusion through a capillary die, at suffi-ciently low extrusion rates, the polymer’s surface issmooth as it exits from the die. At progressively higherextrusion rates, a series of flow instabilities occurs. Thefirst instability that may occur is known as sharkskin orsharkskin melt fracture and is characterized by surfaceroughness. At higher extrusion rates, one observes anoscillating stick-slip transition, followed at higher rates bygross melt fracture in which the polymer is extruded in anextremely irregular fashion. The occurrence of the instabili-ties is dependent on many factors, including polymerchemistry, molecular architecture, molecular mass anddistribution and polymer/wall surface interactions.

Figure 2: High-speed video microscopy reveals that thepolyethylene splits into a core region and a surface re-gion as it exits the capillary tube.



17

relevance by use of polyethylene processed by twin-screwextrusion.

In one set of experiments, we use high-speed video micros-copy to monitor the kinetics of the flow discontinuity out-side the die (Figure 2). We found that the polyethylenematerial splits cohesively into a slow moving surface regionand a fast moving core region, the latter contains the major-ity of the material. The surface region bulges upwards andthen breaks off from the exit lip.

When we monitor the flow kinetics inside the capillarytube, we find that the flow kinetics is smooth, even wellabove the onset of the sharkskin instability. Unsteady flowconditions are observed only under shear stresses close tothat of gross melt fracture. Significantly, we find thatsharkskin can occur under conditions of both stick andslip. This observation helps to reconcile many years ofdebate on the question of whether stick or slip boundaryconditions prevail during sharkskin. We find that eitherone is possible, as long as the critical stress at the exit isexceeded!

A crucial test of exit stretching as a cause of sharkskin wasdone by comparing the onset of sharkskin in resins withand without a fluoropolymer additive. We found that theextensional deformation rate was comparable at the onset;the first parameter that has shown to correlate with theonset of sharkskin.

Now that we understand the mechanistic aspects of theinstability, we can concentrate on material related ques-tions. For example, why does long-chain branching andmolecular mass distribution affect this instability, and whyrelated materials (such as polypropylene) suffer much lessfrom this instability?

Figure 3: High-speed images of the exit region as theextrusion rate increases. Figures (B–E) correspond to (A–D) in the first image sequence (Figure 1).

K.B. Migler

Migler, K.B., Lavallée, C., Dillon, M.P., Woods. S.S., Gettinger, C.L., Visualizing theelimination of sharkskin through fluoropolymer additives: Coating andpolymer-polymer slippage, Journal of Rheology 45, 565-581 (2001).

Figure 4: Flow velocimetry inside the tube (x<0) andoutside it (x>0) is shown for the case of the bare surface(upper plot) and in the case of a fluoropolymer additive(lower).

“Our experiments with NIST using their ExtrusionVisualization Facility have resulted in breakthroughsin our abilities to conceptualize and understand howfluoropolymers reduce sharkskin. These measurementtools strongly impact our efforts in new productdevelopment.”

Claude Lavallée3M Canada Company

Contact Information:

19

Combinatorial Methods

The Combinatorial Methods Program develops new mea-surement techniques and experimental strategies neededfor rapid acquisition and analysis of physical and chemicaldata of materials by industrial and research communities.A multi-disciplinary team from the NIST laboratories par-ticipates to address key mission driven objectives in thisnew field, including needed measurement infrastructure,expanded capability, standards and evaluated data.

Measurement tools and techniques are developed toprepare and characterize materials over a controlled rangeof physical and chemical properties on a miniaturized scalewith high degree of automation and parallelization. Combi-natorial approaches are used to validate measurementmethods and predictive models when applied to smallsample sizes. All aspects of the combinatorial processfrom sample “library” design and library preparation tohigh-throughput assay and analysis are integratedthrough the combinatorial informatics cycle for iterativerefinement of measurements. The applicability of combina-torial methods to new materials and research problems isdemonstrated to provide scientific credibility for this newR&D paradigm. One anticipated measure of the success ofthe program would be more efficient output of traditionalNIST products of Standard Reference Materials and evalu-ated data.

Through a set of cross-NIST collaborations in currentresearch areas, we are working to establish the infrastruc-ture that will serve as a basis for a broader effort in combi-

natorial research. A Combinatorial Methods WorkingGroup (CMWG) actively discusses technical progresswithin NIST on combinatorial methods through regularmeetings. The technical areas and activities of the CMWGare available in a brochure “Combinatorial Methods atNIST” (NISTIR 6730). Within MSEL, novel methods forcombinatorial library preparation of polymer coatings havebeen designed to encompass variations of diverse physi-cal and chemical properties, such as composition, coatingthickness, processing temperature, surface texture andpatterning. Vast amounts of data are generated in a fewhours that promote our understanding of how these vari-ables affect material properties, such as coatingswettability or phase miscibility. Additional focus areas forboth organic and inorganic materials include multiphasematerials, electronic materials, magnetic materials,biomaterials assay, and materials structure and propertiescharacterization. State-of-the-art on-line data analysistools, process control methodology, and data archivalmethods are being developed as part of the program.

In order to promote communication and technology trans-fer with a wide range of industrial partners, an industry-national laboratories-university combinatorial consortium,the NIST Combinatorial Methods Center (NCMC) is beingorganized by MSEL. The NCMC will facilitate direct inter-actions on combinatorial measurement problems of broadindustrial interest and efficient transfer of the methodsdeveloped to U.S. industry.

Alamgir Karim


Contributorsand

Collaborators:

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High-ThroughputMeasurements ofCrystallization andNucleation in Polyolefins

A. Karim, K.L. Beers, A.P. Smith, M. Walker, and J.F. Douglas (Polymers Division,NIST)

Figure 1. The measured rates, G, as a function of crystalli-zation temperature, T. (Curve is data from J. Boon, et al., J.Polym. Sci., Pt. A-2, 1968, 6, 1971.)

The ability to direct or suppress order in polymeric thinfilms has many practical implications for industrial materials.In particular, the degree of crystallinity in semi-crystallinepolymer films can be affected dramatically by a host ofprocessing conditions such as solvents, thermal history,additives, etc. Developing a high-throughput method ofscreening these effects has the potential to quickly optimizethe processing of materials, as well as probe many of theoutstanding theoretical issues regarding the nature of poly-mer crystallization.

The gradient film technology developed at NIST presenteditself as a promising solution. Concerns regarding the conti-nuity of the films, however, prompted a general “proof ofprinciple” test application. Hence, isotactic polystyrene,iPS, extensively a slowly crystallizing polymer, was investi-gated. In one continuous film, the crystal growth rates, G,

The morphology and degree of crystallinity in semi-crystalline thin films has a dramatic impact on theirperformance factors such as stability, optical propertiesand conductivity. Since the parameter space governingthis problem is large and the theoretical understandingof thin-film crystallization is limited, we study a modelpolymer (isotactic polystyrene) as well as isotacticpolypropylene using combinatorial, high-throughputmethods. The effects of film thickness, under-coolingtemperature and nucleating agents are currently underinvestigation. The morphology and kinetics of spheru-litic structure growth is investigated combinatorially.

were measured as a function of temperature and film thick-ness, yielding data from one experiment, which previouslywould have required the preparation of dozens of discretefilms.

The films were prepared using the gradient flow coatingtechnique. Crystal growth was observed using a NikonOptiphot optical microscope and crystal structure analysiswas carried out using a Nanoscope Dimension Seriesatomic force microscope.

Because iPS crystallizes comparatively slowly, it is pos-sible to study the kinetics over a wide range of tempera-tures, from just below T

m to close to the glass transition

temperature, Tg. In this case, a span of 70 °C was typically

covered (from 130 °C to 200 °C), a range in which it hasbeen shown that the rate passes through a maximum be-tween 175 °C and 180 °C. Good agreement was found inthe high-throughput experiment on continuous films forthese rates as a function of temperature (Figure 1). Morerecently, the effects of film thickness, h, on the rate ofcrystallization in iPS thin films were studied; G decreasedwith h below 50 nm. We observed a similar trend in thecontinuous films.

Under similar experimental conditions, isotactic polypro-pylene yields faster, more difficult to measure rates ofcrystallization; however, the dependence of morphologyand degree of crystallization on common nucleatingagents can be observed in conjunction with other param-eters such as h and T. Films containing small amounts ofnucleating agents, such as 4-biphenyl carboxylic acid, andranging in thickness from 50 nm to 150 nm are currentlyunder investigation in the temperature range from 100 °Cto 150 °C .

These results validate the high throughput/combinatorialapproach to investigating polymer crystallization in thinfilms, accelerating the pace of experimentation by increas-ing the parameter space available for sampling. Further-more, the dependence of G on h and T was explored in twodimensions to a degree previously considered unfeasible.

Kathryn L. Beers, Alamgir Karim


Contributorsand

Collaborators:

21

Combinatorial Mapping ofPolymer Film Wettability

Karen M. Ashley, Amit Sehgal,D. Raghavan, Alamgir Karim

A. Sehgal, J.F. Douglas, A. Karim (Polymers Division, NIST)

K. Ashley, D. Raghavan (Howard University, Washington DC)

The ubiquitous use of polymer films in protective coatings,paints, inks, and adhesive layers relies on the ability of thepolymer to spread effectively on or “wet” the underlyingsubstrate. The advent of conducting polymers, molecularelectronics, and polymers in the photonics and electronicsindustry, and the concurrent drive to smaller devices havefurther extended use of ultrathin films, where film stability iscritical to the performance of the device. Conversely, afundamental understanding of stochastic processes such asdewetting generates nano- to micro-scale surface structuresthat may be utilized for optical and biological applications.

Interfacial interaction of the polymer with the underlyingsubstrate is one of the key parameters that influence thestability of thin polymer films. An approach to preparinggradient energy surfaces is developed, by immersing anSi-H passivated silicon wafer in Piranha solution (H

2SO

4/

H2O

2/H

2O) at a controlled rate, producing a monotonic

variation of solvent (water and di-iodomethane) contactangles across the surface. As expected, regions of the sub-strate that had longer exposure to the Piranha solution andhigher concentrations of H2SO4 in the Piranha solutionwere more hydrophilic (lower water contact angles).

Thickness gradients of low molecular mass polystyrenewere prepared on the chemical gradient wafers orthogonalto the surface energy dispersion using a velocity-gradientknife-edge coating apparatus. Film thickness (h) of thecoating was measured by automated spectroscopic spotinterferometry producing contour maps of film thickness.Thus, a typical combinatorial library sample film is preparedto map efficaciously thin-film wettability.

Combinatorial sample libraries were screened by reflectionoptical microscopy for dewetting behavior. Composite im-ages were obtained as shown in the figure, characterized bysubstrate water contact angle and initial film thickness ofpolystyrene given in parenthesis. Dewetting occurred bythe growth of small circular holes whose rims impinge toform small polygons within 2 h of annealing time at 100 °C.We performed a quantitative analysis of the dewet struc-tures by dividing the combinatorial library into a virtual

The stability of thin polymer films is of primary signifi-cance not only in their extensive application as photore-sists, paints and adhesives, but increasingly in electronicand photonic devices and in the biomedical industry.Knowledge of failure mechanisms of thin polymer filmbreakup, in the context of variables such as substratesurface energy, thickness and temperature, is crucial fortheir applicability. We use combinatorial methods toexplore rapidly parameter space to map regions of filmwettability and simultaneously further fundamental un-derstanding of thin-film rupture.

array of individual cells with varying contact angles and filmthickness values. By using an automated batch program,the images were thresholded and the number of polygonsdetermined.

The local polygon density (Np per unit area in an image

box) of dewetted polymer was found to obey a power-lawrelationship with film thickness (N

p~h-4.3) that is in agree-

ment with reported literature value for ultra-thin films onstrongly hydrophilic surfaces (spinodal-dewetting regime).After validating the high-throughput screening method bycomparison to previous studies of thickness effect on de-wetting, a novel power-law relationship between the watercontact angle of the substrate (θ

water) and the number of

polygons of dewetted polystyrene film at constant thick-ness was also established to be (N

p~θ

water-3.6). These studies

suggest that the late-stage dewet polymer pattern dimen-sions are critically sensitive to surface hydrophilicity andfilm thickness.

A more versatile and critical approach to preparing gradientenergy surfaces is being developed by depositing chloro-silane self-assembled monolayers on silicon surface fol-lowed by exposure to UV radiation. Combinatorial librariesof a biocompatible polymer poly(DL-lactic acid), and phaseseparated blends with poly(ε-caprolactone) for use as pat-terned templates for cell proliferation studies are beinginvestigated on these surfaces.


Contributorsand

Collaborators:

22

Anisotropic AdhesionBetween Polymers,Metals, Ceramics andBiomaterials

A.J. Crosby, A. Karim, E.J. Amis (Polymers Division, NIST)

Figure 1: PDMS microlens used for combinatorial adhe-sion test.

We have developed a combinatorial technique to investi-gate adhesive interactions between a polymer and anotherpolymer, ceramic or metal. The primary goal in the develop-ment of this technique was to design a high-throughput,parallel processing adhesion test that allows the adhesivestrength dependence on multivariable parameters and envi-ronmental conditions to be determined.

This combinatorial methodology for measuring polymeradhesion is largely built upon the theory of Johnson,Kendall, and Roberts (JKR), which facilitates the measure-ment of adhesive forces between two contacting surfaces.In the classical use of this theory, a hemispherical lens ofone material is brought into contact with a complementarysubstrate, and subsequently separated. In our work, ratherthan using a single hemispherical lens, we use an array ofmicrolenses. During this process, the contact area anddisplacement of each microlens is recorded through the useof an image acquisition system integrated with an opticalmicroscope. With these parameters, the JKR theory canthen be used to quantify the adhesion energy between thetwo contacting materials. Along each axis of the array, agradient in different environmental parameters or materialproperties can be placed. Examples of such gradient proper-ties are: surface energy, temperature, thickness, crosslinkdensity, blend composition and strain. If two orthogonal

Alfred Crosby, Alamgir Karim, Eric J. Amis

Polymer adhesion is important to numerous technologiesincluding electronic packaging, coatings and paints,biomedical implants, and pressure-sensitive adhesives.Current methods for characterizing adhesion are eitherinefficient or ineffective. Here we develop and implement acombinatorial method to qualitatively and quantitativelymap polymer interfaces to assess the dependence of aniso-tropic polymer adhesion on multivariable parameters. Thistechnique allows us to not only identify optimal environ-ments for the adhesion of given polymer interfaces, butalso facilitates the fundamental investigation of howmolecular structure and chemistry define adhesion.

gradients are placed on the array, then each microlens con-tact point will yield a measurement of adhesion for a uniquecombination of parameters. With our current microlenslibraries, we are capable of measuring 1,600 different pointsof adhesion within a single test.

To demonstrate this methodology, we investigated theeffect of thickness and temperature on the self-adhesion ofpolystyrene (PS). In this test, a microlens array was madefrom poly(dimethylsiloxane) (PDMS). Onto this PDMSarray, we floated a thin layer of PS containing a thicknessgradient. The complementary substrate for this test was aPS-coated silicon wafer with an applied temperature gradi-ent. During contact, the PS molecules diffuse across theinterface, entangle, and strengthen the interface, thus caus-ing the PS coating of the PDMS microlenses to delaminatewithin the contact regions. This “welding” of the contactareas occurs above a critical temperature and below a criti-cal thickness over the time scale of our test. This measure-ment is useful for the microelectronics industry where adhe-sion of thin polymer layers determine the integrity ofelectronic packaging, but the general technique will haveimpact on the numerous industries where adhesion plays adominant role.

Figure 2. Temperature and thickness dependence oncritical PS welding temperature.


Contributorsand

Collaborators:

23

Cellular organization in tissue is guided by or even alteredby the extra-cellular matrix, a heterogeneous complex envi-ronment, comprising of spatially distributed structural andfunctional components. We utilize blend phase separationto create novel multi-component biomimeticmaterials, where theintrinsic heterogeneityis exploited to build instructure and function.We are also motivatedby the awareness thatthe biomedical industryis constrained to theuse of relatively fewmaterials approved byregulatory bodies,often compromising onthe mechanical or thefunctional demands ofthe medical device. Theuse of blends of ap-proved materials,where one componentprovides bioreceptivefunctionality while theother provides thestructural reinforce-ment, greatly enhancesthe range of biocompati-ble materials available tothe industry to improve ultimately the performance of medi-cal devices. Further, we harness the physics of blend phaseseparation in confining geometries of thin films and chemi-cally patterned substrates to create highly structured poly-meric templates to guide and test cellular response.

Pattern-directed phase separation of polymer blends wasused to create libraries of spatial distribution of bio-receptivity. The substrates are patterned chemically by soft

Patterned PolymericSubstrates for DirectedCell Growth

Amit Sehgal, Alamgir Karim, Eric J. Amis

The new paradigm for clinically relevant biomaterials isinspired by nature itself. The level of complexity inherentin the organization of tissue is extended to the design ofbiomaterials with a high level of control of surface func-tionality and topography. We combine the rich micro-structure of polymer blends with tools such as surfacepatterning to create unique highly structured test-substrates for cell response. These surfaces have a system-atic variation of spatial scales and properties across asingle test-substrate to assay optimal structure for cellu-lar reception in a high-throughput fashion.

lithography to have a range of stripe pattern sizes onsingle test substrates. The self-organization of a biode-gradable blend of poly(ε-caprolactone) [PCL] and poly(D-L lactic acid) [PDLA] on the chemical stripe patterns thengenerates a model blend substrate to correlate cell re-sponse to the scales of spatial distribution and size of theblend components. Here, the PCL comprises the semi-crystalline structural component while the PDLA is themore bioreceptive hydrophilic component.

Evaluation of response of osteoblast-like mouse calvarial(MC3T3) cells on the phase separated patterns showsanisotropic cell focal adhesion specifically to the PDLArich phase where the underlying material anisotropyguides the preferential cell orientation (Day 1). This isfollowed by anisotropic liquid like cell spreading (Day 3)where the cell pseudopodia develop preferentially alongthe PDLA rich ridges. This behavior is also found in thenon-patterned isotropic regions but the cell spreading isisotropic. It was also found that the periodicity of the focaladhesion is regulated by the underlying pattern frequency.The systematic variation of surface structure enables us tointerrogate the effect on possible cytoskeletal rearrange-ment and regulation of specific pathways and ultimatelyguide cell function.

Figure 1. Anisotropic cell adhe-sion on PCL/PDLA patterns.

A. Sehgal, A. Karim, J.F. Douglas, E.J. Amis, C.G. Simon, Jr. (Polymers Division,NIST)

Figure 2. Pattern directed cell spreading. (Day 3)


Contributorsand

Collaborators:

24

LCM was designed to target specific cell populations (can-cerous cells) from tissue sections to study genetic muta-tions without “contamination” from surrounding (healthy)tissue. Resuspension in aqueous media however limitsanalysis of the extracted DNA, RNA and proteins from thecaptured cells due to high levels of dilution. This motivatesencapsulation of captured cells in tailor-made microwellswith femtoliter volumes preserving high macromolecularconcentrations with increased sensitivity enabling newdetection and in-situ analysis methods.

Our method of laser-induced fabrication simply employs theuse of an absorbing dye in a thin polymer films creatingthermally induced microchannels and microwells. Given the

Microwell Arrays for LaserCapture Microdissection(LCM)

Giovanna Cantoni, Amit Sehgal,Robert F. Bonner, Alamgir Karim

LCM was developed as a prototype research tool at theNational Institute of Child Health and Development(NICHD) and the National Cancer Institute(NCI) of NIH.It refers to a microscope equipped with a laser to targetand capture single cancerous cells from frozen tissuesections on a fusible polymer film. We have developedmethods to augment the LCM by enabling encapsulationof the captured cells in microwells of femtoliter (10-15 L)volumes with minimal dilution enabling in-situ singlecell analysis. We demonstrate the use of combinatorialmethods for mapping parameter space for laser-inducedmicrofabrication of microwell arrays.

range of variables (laser power, pulse duration, spot size,film thickness, dye concentration, thermal conductivity ofthe film, substrate, etc.) we resort to combinatorial methodsfor high-throughput mapping of microfabrication param-eters. An example of high-throughput characterization (Fig-ure 1) of a grid of programmed contiguous atomic forcemicroscopy scans of a microwell array maps the effect oflaser power and pulse duration on critical microwell dimen-sions while other parameters (dye concentration, thickness)on a single surface are held constant. The wells form idealreceptacles for captured dried tissue (Figure 2).

The thermally induced fabrication process is extremelysensitive to the thickness of the insulating polymer film orproximity to the thermally conductive glass substrates.Section profiles confirm the expected increase in depth withpulse duration that becomes constant as the well nears thepolymer glass interface. This suggests an ablative processthat ceases as thermal conduction to the glass lowers thepeak surface temperature of the depleting polymer layer. Anopposing effect was discovered at lower laser powers,suggesting a non-ablative mechanism whereby a locallyfused film (lower peak temperatures) buckles to form a me-niscus due to the differential in surface tension of the fluidand the surroundings. This process allows for a novelmethod for structuring thin films without chemical modifica-tion (oxidation or etching).

A. Sehgal, A. Karim (Polymers Division, NIST)

G. Cantoni, R.F. Bonner (LIMB/NICHD, NIH)


Contributorsand

Collaborators:

25

Newell R. Washburn and Alamgir Karim

A method for preparing polymeric scaffolds for tissueengineering without the use of organic solvents hasbeen developed. Borrowing techniques from polymerprocessing, a biocompatible polymer such aspoly(ε-caprolactone) or poly(ethyl methacrylate) isblended with a biocompatible, water-soluble polymersuch as poly(ethylene oxide). After annealing the blend,the water-soluble component is dissolved yielding aporous material. The pore connectivity and characteristiclength scale may be controlled by tuning the blend com-position and annealing time and temperature. In thiswork we have focused on blends that have a continuousnetwork of pores and length scales ranging from 10 µm to100 µm.

We are using these scaffolds to investigate several fun-damental issues in tissue engineering such as the influ-ence of scaffold composition, dimensions, and structuralanisotropy on cell proliferation and matrix deposition.Concomitantly, we are also developing new techniquesfor characterizing both the materials and the tissue devel-opment in them.

Figure 1 shows images of poly(ethyl methacrylate) scaf-folds that were prepared with a continuous network ofpores having a characteristic dimension in excess of 100micrometers. The scaffold was seeded with primary chickosteoblasts and cultured in a perfusion bioreactor for 6weeks. Afterwards, the cell-scaffold constructs werefixed and stained for collagen using Sirus Red and min-eral using von Kossa then sectioned using standardhistological techniques. The stained areas in the porousstructure are areas where significant matrix depositionhas occurred.

In collaboration with researchers at the Armed ForcesInstitute of Pathology and National Institutes of Health,we have been developing the use of magnetic resonanceimaging for studying tissue development in situ. In Fig-ure 2 are shown the T1 and magnetization transfer (MT)scans for these scaffolds after 5 weeks of culture. The

Tissue Development inCo-extruded PolymerScaffolds

A method for preparing tissue engineering scaffolds usingtechniques borrowed from polymer processing has beendeveloped. Characterization of tissue development inthese scaffolds is under way in collaboration with re-searchers at the Armed Forces Institute of Pathology(AFIP) and the National Institutes of Health (NIH). Pri-mary chick osteoblasts were cultured on the scaffolds in aperfusion bioreactor and matrix deposition was moni-tored using magnetic resonance imaging and histology.

image shown is a cross-section of a 2-mm-thick disk and thespatial resolution of the scans is 100 µm. The T1 scan hasblack regions where water has been excluded from regionsof mineral deposition and the MT scan has bright regionswhere collagen deposition has occurred. The contrast in thescans is consistent with the observation that the cell cover-age is likely inhomogeneous, leading to inhomogeneousmatrix deposition.

N.R. Washburn, A. Karim, J.P. Dunkers, E.J. Amis (Polymers Division, NIST)

K. Potter (AFIP), F. Horkay (NICHD, NIH)

Figure 1. Histology sections of scaffolds that were stainedfor mineral (left) and collagen (right). The field of view is100 µµµµµm.

Figure 2. Magnetic resonance imaging scans for mineral(left) and collagen (right). The image is a cut through thescaffold, which is 2 cm in diameter.

Current work is focused on calibrating the magnetic reso-nance signal for performing quantitative assessment oftissue development and addressing the fundamental issuesrelated to tissue engineering discussed above. We also areattempting to develop functional imaging techniques thatyield more information about metabolic activity of the cells.

26

Interface of Materials with Biology

New materials and devices are changing radically the medi-cal treatment of injury and disease, yet because of the rapidgrowth of this segment of the materials industry, an ad-equate measurement infrastructure does not exist. Theprogram on the Interface of Materials with Biologydevelops measurement methods, standards, and fundamen-tal scientific understanding at the interface between materi-als science and biological science. Within the health careindustry we focus on dental and medical sectors that applysynthetic materials for replacement, restoration, and regen-eration of damaged or diseased tissue.

Four major activities constitute this program:

• The dental industry is composed largely of small manu-facturers with very little R&D capability. The dentalmaterials projects, carried out in close collaboration withthe American Dental Association fill that need by devel-oping improved materials and techniques, patentingthese inventions, licensing to these small companies,and most importantly, providing technical assistance tothese licensees for producing and improving their prod-ucts. This has provided U.S. companies with productsthat successfully compete on a worldwide market. Ourresearch focuses on improved understanding of thesynergistic interaction of the phases of polymer-basedcomposites and the mechanisms of adhesion to dentinand enamel. This approach will ultimately lead to materi-als with improved durability, toughness and adhesion tocontiguous tooth structure.

• The tissue engineering industry shows the potential forexplosive growth in the coming years as biomedicalresearch is moving from academic science to industrialapplication at an increasing rate. Our work seeks tobridge the gap between knowledge generation by cellbiologists and product development in industry. Incollaboration with the NIST Biotechnology Division weare developing a set of measurement methodologies andreference materials to use in assessing interactions incomplex systems of living cells with synthetic materials.The expected outcomes of this work include referencesubstrates that induce gene expression associated withspecific stages in cellular activity, and engineered DNAvectors that signal fluorescently these responses inadherent cells.

• Regenerating form and function to bone defects in anelderly, osteoporotic population of Americans willbe a daunting challenge. To meet this challenge, we aredeveloping metrology methods to characterize thebiocompatibility of bone grafts for bone regeneration.Quantitative methods being developed include bioas-says for the adhesion, viability, proliferation, and alka-line phosphatase activity of bone cells, as well as confo-cal microscopy and optical coherence tomography formeasuring the growth of bone cells into bone grafts. Acombinatorial approach is being used to rapidly identifycompositions and surface features of bone grafts thatprovide desirable properties such as biocompatibilityand mechanical durability.

• The NIST Center for Neutron Research and the NISTBiotechnology Division are engaged in the study ofbiomimetic films that serve as models of cell membranesand which are of fundamental importance in understand-ing such key biological processes as phospholipid self-assembly, molecular recognition and cell-protein interac-tions. Recent improvements in neutron reflectometry atthe NCNR, coupled with advances in biomimetic filmfabrication at metallic interfaces pioneered in the Bio-technology Division, afford enhanced sensitivity forprobing membranes and membrane-protein complexes.New phase sensitive measurement techniques andmodel-independent data analysis methods have demon-strated the feasibility of obtaining reliable depth profilesof membrane structures in contact with biologicallyrelevant aqueous environments, achievingsubnanometer spatial resolutions.

Fundamental to all the work in this program is the recogni-tion that surfaces and interfaces play a critical role in bio-logical systems and, in particular, in the interactions ofsynthetic or designed materials with biological systemsand function. By providing the unique expertise in theNIST Materials Science and Engineering Laboratory tocharacterization of surfaces and interactions at interfaces inbiomaterials we will accelerate the introduction of improvedmaterials and help provide the means to assure qualitycontrol that is critical to this industry.

Contact Information: Eric J. Amis

Interface of Materials With Biology

Contributorsand

Collaborators:

27

It is well known that the primary (amino acid sequence),secondary (beta sheet, alpha helix, etc.) and tertiary(folded) structures of a protein are crucial for enzymaticactivity. However, dynamics ranging from the picosecondthermal fluctuations to the millisecond (and slower) con-formational changes are also requisite for biological func-tion. At the high frequency end, neutron scattering quan-tifies the local thermal fluctuations in terms of a meansquare atomic displacement <u2>. Several studies haveshown that in hydrated proteins there is a dynamic transi-tion, T

d, near 180 K to 220 K (reportedly the T

g of super-

cooled water) where a sudden change of <u2> occurs andabove which the thermal fluctuations become stronglyanharmonic. It is also known that T

d coincides with the

onset of enzymatic activity. These fluctuations arethought to enable the large-scale conformational changesthat accompany biological function.

The Dynamic Effects ofProtein Stabilization inGlass Forming Liquids

Christopher L. Soles, Amos M. Tsai

The stability of protein and enzyme molecules is of greatinterest to the pharmaceutical industry. However, themain attributes constituting a stable environment are notyet fully identified. Excesses in temperature and/or dehy-dration irreversibly damage most enzymes, proteins, andcellular structures. While a few viscous alcohol or sugarco-solvents are known to provide this stability, the re-sponsible mechanisms are poorly understood. Inelasticneutron and low-frequency Raman scattering are used toprobe the dynamic effects of these viscous sugars/alcohols to help resolve the mechanisms of proteinstabilization.

peratures commensurate with its own glass transition. It isbelieved generally that the reduced mobility imparted bythe viscous glycerol, a widely used cryo-protectant inbiological freeze-drying processes, is vital for stability.

This leads to the notion that a high Td is desirable in a

protein stabilization scheme. However, there is more toprotein stabilization than glass formation alone. Below T

dglycerol suppresses <u2> the harmonic motions oflysozyme. This is quantified as a stiffening of the elasticforce constant defined by the thermal evolution (i.e.,slope) of <u2>; stiffer vibrations increase less dramaticallyin amplitude with T. From the previous figure, glycerolstiffens the force constants of lysozyme by 40 percent.

The effects of this vibrational stiffening are also seen inthe full inelastic neutron scattering spectra. The positionsof the Boson peak of the dry and glycerol-preservedlysozymein are analyzed in terms of their force constant. Inglycerol the low-frequency mode is shifted to higher ener-gies compared to dry state at the same temperature. Thisshift occurs at the same temperatures where the suppres-sion of <u2> is observed. If this low-frequency vibrationis modeled as a harmonic oscillator (ω2 = k/m), the squareof the peak frequency also stiffens by 40 percent, mirror-ing the <u2> data.

The similarities in <u2> and the low-frequency vibrationalspectra suggest that a stabilized protein also has a higherfrequency Boson peak. Recently we corroborated this inmesophilic and thermophilic (thermally stable) a-amylase;both a suppressed <u2> and higher frequency Bosonpeak are seen in the naturally thermophilic protein. Thisprovides a powerful tool to assess new preservationschemes, a process currently done by trial and error. While<u2> measurements are limited by the availability of neu-trons, Boson peak measurements are accessible with con-ventional low-frequency Raman scattering. This mayprovide the pharmaceutical industry a readily availabletool to help evaluate protein stabilization schemes.

J.F. Douglas (Polymers Division, NIST)

R.M. Dimeo, D.A. Neumann, R.L. Cappelletti (Center for Neutron Research, NIST)

G. Caliskan, A. Kisliuk, A.P. Sokolov (University of Akron), M.T. Cicerone(Brigham Young University), J.J. DePablo (University of Wisconsin)

0.20

0.15

0.10

0.05

0.00

∆ <

u2 > (

Å2 )

350300250200150100T ( K )

glycerol dry wet

kdry = 8.8 N/m

kglycerol = 12.0 N/m

fit range

In proteins stabilized with a viscous alcohol/sugar co-solvent, T

d typically shifts to higher temperatures. This is

seen in the above figure where the dynamics of dehy-drated, hydrated, and glycerol-preserved chicken eggwhite lysozyme are compared. Glycerol shifts T

d to tem-


Contributorsand

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28

This project is directed toward enhancing our basic under-standing of how monomer structure and variations incomonomer compositions influence the photopolymeri-zation process and the polymeric network structure, bothcritical factors that determine the potential properties thatcan be achieved with dental polymers and their derivedmaterials, e.g., composite restoratives. Dental matrix poly-mers are described often simply as highly cross-linkednetworks with little or no characterization done beyond ameasurement of overall vinyl conversion. Although theresults of physical and mechanical property testing alsohave been reported widely for dental polymers, these datawould be more useful with knowledge of how monomerstructure and resin composition variations affect the de-velopment of cross-linked polymers. Generally this infor-mation is difficult to interpret and use as a guide for thedevelopment of improved materials.

In addition, the project is intended to define thecurrently unknown co-reactivity of structurally differentco-monomers that are typically used in dental polymers.For lack of this information, the reactivity and cross-link-ing potential of dental resins are generally assumed to beequal. The use of selected model monomers is designed todemonstrate the influence of specific structural featureson polymer properties and should have significant impacton the development of improved materials. An examinationof non-methacrylate co-monomers, such as vinyl estersand vinyl ethers, offers a means to modify network forma-tion and also appears to allow for higher conversion andimproved mechanical properties.

It is known that widely used dental monomers such as thehydroxylated dimethacrylate Bis-GMA and the urethanedimethacylate UDMA form strong hydrogen bonds thatare of different types. The effect of hydrogen bonding onmonomer viscosity is well known, but its influence on thepolymerization process and its potential to influence net-work structure has been overlooked. These aspects arebeing examined along with studies of some model hydro-gen bonding monomers that directly may provide poly-

Structure-PropertyRelationships in DentalPolymers

Joseph M. Antonucci

Polymer-based dental materials are used increasingly indentistry and allied biomedical fields. As part of a jointresearch effort supported by the National Institute ofDental and Craniofacial Research and also involvingcollaboration with the American Dental AssociationHealth Foundation Paffenbarger Research Center, NISTis providing the dental industry and the dental profes-sion with a comprehensive knowledge base regardingpolymeric dental materials that will help elucidate thein-vitro and in-vivo performance of these materials.

mers with improved properties. An interesting example ofthe profound effects of hydrogen bonding involved thecomparison of 2-hydroxyethyl methacrylate (HEMA) withits isomer, ethyl-α-hydroxymethylacrylate (EHMA). Thestronger intramolecular hydrogen bonding of EHMA vs.HEMA has a significant effect on both monomer andpolymer properties. Also, subtle changes in monomerstructure, for example the substitution of ether linkagesinto a predominantly hydrocarbon dimethacrylate, canproduce dramatic differences in polymerization rate andpolymer properties. The systematic introduction of het-eroatoms into dimethacrylate monomers currently is beingexamined to explain why these differences exist and howthey can be employed to obtain polymers with improvedproperties. The use of multi-modal distributions of co-monomers with varied chain lengths offers a simple meansto achieve an increased level of vinyl conversion, networkstructure variations in the polymer and correspondingimprovements in the physical, chemical and mechanicalproperties of dental polymers and derived materials.

A major part of this project is directed at implementingstrategies of maximizing vinyl conversion while minimizingpolymerization shrinkage. Currently we are investigatinghigh molecular mass urethane and silyl ether derivatives ofBis-GMA, as well as new types of high molecular massdiluent monomers, for their efficacy in reducing residualvinyl unsaturation, polymerization shrinkage and the wateruptake of their polymers. In addition, the use of alternativeinitiator systems are under investigation in an effort toenhance photopolymerization efficiency and alter polymernetwork formation. This project is expected to lead to abetter understanding of structure-property relationshipsof monomer/resin systems that should translate into poly-meric dental materials with improved clinical performance.The results of these studies should extend well beyondthe dental materials venue to include a significant numberof other applications that rely on the rapid formation ofcross-linked polymeric network having optimal propertiesfrom photopolymerizable monomer systems.

J.M. Antonucci, M.D. Weir, D.W. Liu, C.A. Khatri (Polymers Division, NIST)

S. Dickens (American Dental Association Health Foundation PaffenbargerResearch Center)

J.W. Stansbury (University of Colorado, Boulder)


Contributorsand

Collaborators:

29

Over 100,000 operations requiring bone grafts are per-formed each year in the United States to repair osseousdefects resulting from trauma or disease. Autografts arewidely used by surgeons, but the amount of bone avail-able for autografts is limited and available material is diffi-cult to shape. Thus, the development of synthetic materi-als for use as bone grafts is a primary objective of thetissue engineering community. We are using this opportu-nity to develop metrology to serve this burgeoning indus-try and to develop a novel composite bone graft.

Our graft consists of a calcium phosphate powder andsmall spheres made from a biodegradable polymer that aremixed with water to form a paste. The paste can be moldedand then sets like cement within 30 min to form a solidmatrix of microcrystalline hydroxyapatite that contains thepolymer spheres. In vivo, the spheres should degrade toleave behind macropores for colonization by bone tissue.We are assessing the biocompatibility of the compositegraft and are making the graft osteoinductive by addingbone growth factors.

By facing challenges that are common to the entire tissueengineering industry in the context of this real problem, wecan evaluate and improve the existing biocompatibilitymetrology. Specifically, we have implemented new tech-niques for assessing cell morphology, adhesion and prolif-eration during culture on opaque substrates such as ourbone graft. We are characterizing new fluorescent indica-tors of cell viability (see figures) and are improving uponcell preparation techniques for environmental scanningelectron microscopy which allows high-resolution imagingof hydrated samples. In addition, we are evaluating a newcolorimetric assay for quantifying cell number that iseasier to use and faster than standard assays.

After characterizing our composite bone graft with thesenew techniques, we will move to make the best techniquesinto standardized assays with the appropriate agencies(ANSI, ASTM, FDA, ISO). Thus, this project may yield anew synthetic bone graft material as well as new standardsfor use by the tissue engineering industry.

A Moldable, Resorbable,Macroporous, CompositeBone Graft ContainingGrowth Factor

Carl G. Simon, Jr., Chetan Khatri,Francis W. Wang

The rapidly expanding tissue engineering industry is inneed of improved measurement technology to aid in thedevelopment of new biomaterials. We are developing thistechnology through the design and testing of a novelcomposite bone graft. Techniques for assessing cell mor-phology, adhesion and proliferation on opaque speci-mens are being evaluated with the aim of proposing thebest assays as new standards to appropriate agencies(ANSI, ASTM, FDA, ISO). Thus, this project can yield anew synthetic bone graft as well as new standards for useby the tissue engineering industry.

F.W. Wang, C.G. Simon, Jr., C.A. Khatri, S.A. Wight, J.F. Hsii (Polymers Division,NIST)

W. Guthrie (Statistical Engineering Division, NIST)

Shozo Takagi (American Dental Association Health Foundation)

Cells growing on a bone graft specimen which has beenfluorescently double-stained for live (green, top) and deadcells (red, bottom). Both panels are the same field of viewseen through different filters.


Contributorsand

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30

Over the broad range of solution conditions when precipi-tation occurs spontaneously, amorphous calcium phos-phate (ACP) precedes the formation of HAP. ACP hasbeen shown to have high solubility in aqueous media andto undergo rapid conversion to HAP, especially at lowpHs. Both of these properties suggest its use as abioactive filler in polymeric materials for the preservationor repair of enamel, dentin, cartilage and bone.

Utilizing conventional dental matrix resins (e.g. 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl] propane (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA) and2-hydroxyethyl methacrylate (HEMA)) and ACP or modi-fied versions of ACP as a filler phase, we have preparedphotopolymerizable bioactive composites that had ad-equate physicochemical and mechanical properties andtheir bioactivity resides in the remineralization potential ofACP as a consequence of the sustained release of calciumand phosphate ions into simulated saliva media.

However, compared to conventional glass-filled compos-ites, ACP composites are still relatively weak in mechanicalstrength. In an effort to improve their reinforcing capabili-ties, we have modified ACP during its synthesis withglass-forming agents such as tetraethoxysilane (TEOS)and zirconyl chloride. This has resulted in modest im-provement of mechanical properties, such as biaxial flexurestrength. Further improvements may be feasible by the useof coupling agents with these modified ACP fillers andalternative matrix resins. Another strategy for enhancingmechanical properties is to employ hybrid filler phasesconsisting of ACP filler admixed with silanized glass fillersand/or polymer fibers, such as oriented polyethylenefibers. Preliminary studies have yielded encouraging re-sults for all these strategies.

These studies also have shown that certain variations inmethacrylate resin chemical structure and composition

Bioactive PolymericComposites forMineralized TissueRegeneration

Joseph M. Antonucci

Crystalline hydroxyapatite (HAP) is considered to be thefinal stable product in the precipitation of calcium andphosphate ions from neutral or basic solutions and it isalso the structural prototype of the major mineral compo-nent of bones and teeth. Recently, there has been increas-ing interest by biomaterials community in utilizing poly-mers of various types as matrices and as reinforcements(especially in fiber forms) for calcium phosphate-basedcomposites. Customers for this technology include dentaland biomedical manufacturers and practitioners.

may affect the rate and extent of the ion release from ACP-filled composites, the internal conversion of ACP intoHAP, the conversion of methacrylate groups, as well asthe mechanical properties of the composites.

Recent studies have involved assessing the effect ofsubstituting ethyl-α-hydroxymethylacrylate (EHMA) forHEMA. EHMA, a unique isomer of HEMA, is much morehydrophobic than the completely water miscible HEMA.Preliminary results indicate that ACP composites utilizingEHMA are significantly stronger than similar compositesbased on HEMA. In related research, a facile synthesishas been developed for new types of low-shrinking,crosslinking monomers of controlled biodegradability andhydrophilicity that also enable high loadings of ACP incomposites.

These various types of polymeric calcium phosphatematerials are designed to be bioactive, biocompatible andhighly conformable to mineralized tissue. Injectable,photopolymerizable ACP composites appear feasible aswell. All these ACP composites are expected to have sig-nificant remineralization potential and should find use inremineralizing white spots and caries lesions in toothstructure, especially interproximally and gingivally. Ifsuccessful, ACP composites would have significant ad-vantages over other remineralizing therapies. Currently, astrong need exists for protective liners, bases, prophylac-tic sealants and adhesive restoratives that are manipulatedeasily and that can provide efficacious long-term protec-tion against demineralization and even haveremineralization capabilities. In addition, bioactive ACPcomposites with biodegradable polymer matrices mayfind wider applications as therapeutic materials with theability to provide osteoconductive environments condu-cive to promoting bone healing, such as is needed indental (endodontic, periodontal etc.) and other biomedicalapplications.

J.M. Antonucci, M.D. Weir, C.A. Khatri, E.D. Eanes, B.O. Fowler (PolymersDivision, NIST)

D. Skrtic, G.E. Schumacher (American Dental Association Health FoundationPaffenbarger Research Center)


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Materials for Microelectronics

Today’s U.S. microelectronics and supporting infrastruc-ture industries are in fierce international competition todesign and produce new smaller, lighter, faster, more func-tional, and more reliable electronics products more quicklyand economically than ever before.

Recognizing this trend, in 1994 the NIST Materials Scienceand Engineering Laboratory (MSEL) began working veryclosely with the U.S. semiconductor, component and pack-aging, and assembly industries. These early efforts led tothe development of an interdivisional MSEL programcommitted to addressing industry’s most pressing materi-als measurement and standards issues central to the de-velopment and utilization of advanced materials and mate-rial processes within new product technologies, asoutlined within leading industry roadmaps. The vision thataccompanies this program—to be the key resource withinthe federal government for materials metrology develop-ment for commercial microelectronics manufacturing—maybe realized through the following objectives:

• Develop and deliver standard measurements and data;• Develop and apply in situ measurements on materials

and material assemblies having micrometer- andsubmicrometer-scale dimensions;

• Quantify and document the divergence of materialproperties from their bulk values as dimensionsare reduced and interfaces contribute strongly toproperties;

• Develop models of small, complex structures to substi-tute for or provide guidance for experimental mea-surement techniques; and

• Develop fundamental understanding of materialsneeded in future microelectronics.

With these objectives in mind, the program presentlyconsists of 20 separate projects that examine and informindustry on key materials-related issues, such as: electri-cal, thermal, microstructural, and mechanical characteris-tics of polymer, ceramic, and metal thin films; solders,solderability and solder joint design; photoresists, inter-faces, adhesion and structural behavior; electrodeposi-tion, electromigration and stress voiding; and the charac-terization of next generation interlevel and gate dielectrics.These projects are conducted in concert with partnersfrom industrial consortia, individual companies, academia,and other government agencies. The program is coupled

strongly with other microelectronics programs withingovernment and industry, including the National Semicon-ductor Metrology Program at NIST.

FY2001 Projects (and division leading project)

Lithography/Front End Processing

Characterization of Ultrathin Dielectric Films (Ceramics)Lithographic Polymers (Polymers)

On-chip Interconnects

Interconnect Materials and Reliability Metrology (Materi-als Reliability)Measurements and Modeling of Electrodeposited Inter-connects (Metallurgy)Thin Film Metrology for Low-k Dielectrics (Polymers)

Packaging and Assembly

Packaging Reliability (Materials Reliability)Solder Interconnect Design (Metallurgy)Solders and Solderability Measurements for Microelec-tronics (Metallurgy)Tin Whisker Mechanisms (Metallurgy)Wafer Level Underfill Experiment and Modeling(Metallurgy)Wire Bonding to Cu/Low-k Semiconductor Devices(Metallurgy)X-ray Studies of Electronic Materials (MaterialsReliability)

Crosscutting Measurements

Dielectric Constant and Loss in Thin Films and Compos-ites (Polymers)Electron Beam Moiré (Materials Reliability)Ferroelectric Domain Stability Measurements (Ceramics)Measurement of In-Plane CTE and Modulus of PolymerThin Films (Polymers)Mechanical Properties of Thin Films (Ceramics)Permittivity of Polymer Films in the Microwave Range(Polymers)Polymer Thin Films and Interfaces (Polymers)Texture Measurements in Thin-Film Electronic Materials(Ceramics)Thermal Conductivity of Microelectronic Structures (Ma-terials Reliability)

Wen-li Wu

Materials For Microelectronics

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As integrated circuit feature sizes continue to shrink, newlow-k interlevel dielectric materials are needed to addressproblems with power consumption, signal propagationdelays, and crosstalk between interconnects. One avenueto low-k dielectric materials is the introduction of nano-meter-scale pores into a solid film to lower its effectivedielectric constant. Specifics of the pore architecture mayaffect other properties, hence characterization of the porestructure of thin nanoporous low-k dielectric films is criti-cal and beyond the capabilities of conventional methods.

The small sample volume of 1-µm films and the desire tocharacterize the film structure on silicon wafers narrow thenumber of available measurement methods. We have de-veloped a novel combination of small-angle neutron scat-tering (SANS), high-resolution x-ray reflectivity (HRXR),and ion scattering techniques to determine importantstructural and physical property information about thinporous films less than 1 µm thick. These measurements areperformed directly on films supported on silicon sub-strates so that effects of processing on structure can beinvestigated.

During the past year, we focused efforts in three areas:continuing characterization of current industrially relevantmaterials through International SEMATECH, establishingnew collaborations with Rohm and Haas and Dow Chemi-cal, and developing advanced measurement methods formore thorough and accurate film characterization. Interna-tional SEMATECH, a consortium of microelectronics com-panies, provided more than 20 separate samples for char-acterization by NIST, including spin-on glass materials,films from chemical vapor deposition, and organic thinfilms. The structural information provided by NIST isplaced into a master database that includes data from avariety of sources, detailing both the structural and mate-rial properties needed to evaluate candidate materials.

New measurement methods have been developed to morethoroughly and accurately characterize pore and matrixmorphology. HRXR measures the average film thicknessand average density of the wall and voids. By infusing

Characterization ofPorous Low-k DielectricConstant Thin Films

NIST is providing the semiconductor industry withunique on-wafer measurements of physical and structuralproperties of porous thin films important as low-kinterlevel dielectric materials. The methodology usesseveral complementary experimental techniques to mea-sure the average pore and matrix morphology, includingpore size distributions. New methods have been devel-oped to measure pore and matrix morphology in filmshaving complex structures.

Barry J. Bauer, Eric K. Lin, Wen-li Wu

toluene into the voids, the volume fraction of connectedvoids can be measured by HRXR along with the averagedensity of the wall material and closed pores. When thetoluene vapor is lower than the saturated vapor pressure(partial pressure), the small pores fill first, and measure-ment of the overall density by HRXR allows calculation ofthe complete pore size distribution.

Other new techniques being developed include SANSmeasurements on films that have been infused with mix-tures of normal toluene and deuterated toluene. The matchpoint measures where the neutron contrast of the toluenematches that of the wall material. This measures porosityand wall density in a way that is independent from theHRXR measurements and applies to all morphology types.When the match point has been determined, the films canbe infused with the match mixture at various partial pres-sures in a way analogous to the HRXR. Pore size distribu-tions can be estimated from the partial pressure SANS,and at the saturation point, any residual scattering presentgives information on sample heterogeniety.

Figure 1. Representative pore size distribution calculatedfrom HRXR partial pressure measurements.

B.J. Bauer, E.K. Lin, H. Lee, H. Wang, R. Hedden, D. Liu, W.L. Wu (PolymersDivision, NIST)J. Wetzel, J. Lee (International SEMATECH), N. Pugliano (Rohm and Haas),B. Landes (Dow Chemical), M. Baklanov (IMEC), D. Gidley (University of Michi-gan), W. Chen, E. Moyer (Dow Corning), S. Yang (Lucent) H. Fan, C.J. Brinker(Sandia National Laboratory)


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Polymer Fundamentals ofPhotolithography

Eric K. Lin, Wen-li Wu

E.K. Lin, C.L. Soles, J.L. Lenhart, R.L. Jones, P.M. McGuiggan, D.L. VanderHart,W.L. Wu (Polymers Division, NIST)

D.A. Fischer (Ceramics Division, NIST)

D.L. Goldfarb, M. Angelopoulos (IBM T.J. Watson Research Center)

In photolithography a pattern is transferred to the siliconsubstrate by altering the solubility of areas of a polymericphotoresist thin film exposed to light through a mask via anacid catalyzed deprotection reaction. To fabricate smallerfeatures, next-generation photolithography will be pro-cessed with wavelengths of light requiring photoresistfilms less than 100-nm thick and dimensional control towithin 2 nm. Many new material and transport issues arisewhen fabricating structures over these length scales.

To advance this key technology, we work closely withindustrial collaborators to apply high-spatial resolution andchemically specific measurements to understand varyingmaterial properties and process kinetics at nanometerscales. The unique measurement methods we apply includex-ray (XR) and neutron reflectivity (NR), small-angle neu-tron scattering (SANS), incoherent neutron scattering(INS), near-edge x-ray absorption fine structure (NEXAFS),and combinatorial methods. Our efforts focused on thefundamentals of polymer materials and processes thatcontrol the resolution of photolithography including: (1)the physical properties and polymer chain conformationwithin sub-100-nm structures; (2) the spatial segregationand distribution of photoresist components; (3) the trans-port and kinetics of photoresist components and thedeprotection reaction interface; and (4) the structural char-acterization of lithographically prepared structures.

This past year, we made significant progress in eluci-dating molecular behavior of important lithographic pro-cesses. We performed the first measurements of the three-dimensional conformation of polymer chains (SANS) andthe local dynamics of model photoresist polymers (INS)confined in sub-100-nm thin films. These results provideimportant insight into observed deviations in material prop-erties and transport processes within sub-100-nm imaginglayers needed in the future (see Accomplishment Report“Measurement Methods Aid Development of Photoresistsfor Next-generation Photolothography”).

Using NR and XR, we have shown that moisture uptake inphotoresist films (a critical component in some resists) is

Photolithography, the process used to fabricate inte-grated circuits, is the key enabler and driver for themicroelectronics industry. As lithographic feature sizesdecrease to the sub-100-nm length scale, significantchallenges arise because both the image resolution andthe thicknesses of the imaging layer approach macromo-lecular dimensions characteristic of the polymers used inthe photoresist film. Unique high-spatial resolution mea-surements are developed to reveal limits on materialsand processes that challenge the development of photo-resists for next-generation sub-100-nm lithography.

uniform, not segregated to a hydrophilic or hydrophobicsubstrate. Additional NR measurements (Figure 1) showthe interfacial development of partially miscible polymerlayers (similar to soluble and insoluble areas of an exposedresist) with nanometer resolution. We have appliedNEXAFS to measure the distribution of photoacid genera-tor molecules within the top (2–3) nm of the resist filmrelative to the bulk concentration. The surface segregationof important resist components and the resulting chemis-try strongly affect the quality of the fabrication process.SANS measurements of lithographically prepared struc-tures have been extended and applied to new photoresistformulations and structural sizes. Finally, we are applyingcombinatorial methods to quantify quickly important tem-perature boundaries in the compositional dependence ofthe thermal deprotection of photoresist polymers mixtures.

Figure 1. Neutron reflectivity data and real space profilesfrom bilayers of deuterated poly(methyl methacrylate) andpoly(hydroxystyrene). The data show the interfacial evolu-tion over nanometer-length scales.


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Characterizing BuriedPolymer/SubstrateInterfaces

Joseph L. Lenhart

J.L. Lenhart, J.P. Dunkers, W.L. Wu (Polymers Division, NIST)

R.S. Parnas (currently at University of Connecticut), J.H. van Zanten (North Caro-lina State University).

The measurement system consists of chemically attachinga fluorophore, dimethyl-amino-nitro-stilbene (DMANS) to atriethoxy silane-coupling agent, generating a fluorescentlylabeled silane-coupling agent (FLSCA) that bonds withhydroxyl groups on glass or metal surfaces. FLSCA-coatedglass surfaces were immersed in epoxy resin. A blue shift inthe emission maximum from the fluoroprobe and an in-crease in fluorescence intensity could be measured duringresin cure. Since the DMANS probe is grafted into thesilane layer, the fluorescence response is completely fromthe interfacial region. FLSCA was diluted on glass surfaces

While many techniques are available to study polymerfilms and surfaces, very few can probe buried polymer/substrate interfacial regions, which are critical in com-posites, nano-composites, biomaterials, electronics,paints, coatings and adhesives. A technique was devel-oped to probe this interfacial region by localizing afluorescent dye on the substrate surface. The currentwork is focused on applications to glass-reinforcedcomposites, but the technique will be extended formicro-electronics applications to probe interfacialacidity of photo-resist polymers adhered to bottom anti-reflective coatings.

independent of the FLSCA/GPS layer thickness (rightmost graph below). These data show that the composi-tion profile in the interfacial region is influenced by thecompetition between diffusion of resin monomers into thesilane layer, and the reaction kinetics, which slow thediffusion process. Using the transition from incompletepenetration (0.5-µm thick layers) to complete penetration(0.3-µm thick layers), the diffusion constant for resinmonomers into the silane layer was estimated to be in therange of (10-12 to 10-13) cm2/s estimated from D~L2/t

gel,

where tgel

is the resin gel time. The dotted lines representthe total fluorescence shift when the layers were im-mersed in hardener only. Since the amine on the hardener

will react with the epoxy functionality these lines repre-sent the maximum fluorescence shift that is expected fromequilibrium penetration of the resin and silane layer. Thework has resulted in several publications (J. Coll. Inter-face Sci. 221, 75, 2000; Langmuir 16, 8145, 2000; Mac-romolecules 34, 2225, 2001; Optics & Lasers Eng. 35, 91,2001; Polymer Composites, in press; J. Coll. InterfaceSci., submitted).

The technique will be extended to interfaces in microelec-tronics including the photoresist and anti-reflective coat-ing (ARC) interface. To probe the acidity in the interfacialregion, acid sensitive fluorescent probes will be grafted tothe ARC layer.

with glycidoxypropyltriethoxysilane (GPS), a couplingagent used as a surface primer in glass fiber-reinforcedcomposites. Experiments were conducted as a function ofthe FLSCA/GPS layer thickness. The thickest silane layerexhibited a smaller fluorescence shift during cure, suggest-ing incomplete resin penetration into these layers (seeright). The resin was composed of a stochiometric mixtureof diglycidyl-ether-bisphenol A (DGEBA) cured with adiamine hardener polypropylene-glycol-bis-2-aminopropylether (Jeffamine D400 or D230). Two molecular massJeffamine hardeners were used (230 and 400) g/mole. TheDGEBA/D400 system gelled in 30 min, while the DGEBA/D230 resin system gelled in 15 min. When the slower gel-ling resin was used, the fluorescence shift during cure was


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Materials for Wireless Communication

Today, wireless technologies constitute one of the mostimportant growth areas in the global electronics industry.The current revolution in wireless communications wouldnot have been possible without the discovery and devel-opment of oxide ceramics exhibiting the coincidence ofhigh, temperature-independent resonant frequency withlow dielectric loss. Technically important ceramic materialsfall into two major dielectric categories: bulk ceramics forbase station resonators/filters and those needed for low-power, miniaturized hand-held devices. Paramount inachieving smaller and lower cost devices are guidelinesthat facilitate the rational design of advanced materialsto provide temperature stability, frequency, and size-reduction requirements for the next generation of devicesfor cellular, PCS, and many other niches of the wirelesscommunications industry.

A collaboration between the Ceramics Division and theElectrical and Electronics Engineering Laboratory at NISTon ceramic materials for base station applications includesexperimental determination of selected complex-oxidephase diagrams integrated with in-depth structural (x rays,electrons, neutrons), crystal-chemical, spectroscopic, anddielectric property characterization. The objective of thismultidisciplinary project is to determine the fundamentalrelationships between phase chemistry, crystal structure,and dielectric performance at wireless frequencies.

Another project in the Ceramics Division uses first-principles calculations to elucidate the roles of cationorder-disorder and ferroelastic phenomena in determiningthe phase relations and physical properties of complexceramic oxide systems. These calculations are used topredict cation ordering phenomena, physical properties,and how they vary with chemical composition. Criticalexperiments are performed to test the predictions.

Microstructural modeling and experimental studies arealso under way to determine the dimensional changes inlow-temperature-cofired ceramics used for portable com-munication devices. Processing models were identified bya large segment of industrial producers as being crucial toreducing the time currently needed to design and producecomponents. Wireless devices, often hand-held, are espe-cially susceptible to mechanical damage; assuring thereliability of electronic products is especially critical forsuch devices. Work in the Materials Reliability Divisionincludes development of noncontact acoustic metrologyto characterize wireless materials in both thin-film and bulkform. Also, the mechanical properties of thin films areinvestigated using laser-ultrasonic methods to generateand detect surface acoustic waves. The elastic propertyinformation obtained will result in improved predictivemodeling of film performance. In addition, resonant-ultrasonic techniques are applied to new piezoelectricmaterials for SAW devices, used extensively as oscillatorsin hand-held devices.

Researchers in the Polymers Division developed a newtest method that permits dielectric measurements of filmsubstrates at frequencies of 1 to 10 GHz. The project isexploring the relationships between dielectric propertiesand structure in a variety of polymer resins, blends andcomposites, e.g., hybrid materials based on polymer resinsand ferroelectric ceramics. Microstructural modeling andexperimental studies are being undertaken to determine theeffect of polarizability of the polymer matrix on the appar-ent dielectric permittivity of the composite. A need formodels and measurement techniques has been identifiedby a large segment of industrial producers as being crucialin new designs and in reducing the development time ofnew products. A consortium involving the National Centerfor Manufacturing Science (NCMS) and industry has beenorganized to help address these issues.

David J. Vanderah

Materials For Wireless Communication

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Novel dielectric hybrid materials based on organic resinsand ferroelectric ceramics with high-dielectric constantsare being developed by the industry to advance miniatur-ization and functional performance of high-speed electron-ics. These materials are being used to construct integratedpassive devices and de-coupling capacitance films withlow impedance that are embedded within chip substratesand printed circuit sub-assemblies. This new materialapproach is essential as current methods based on dis-crete components cannot provide adequate solutions atfrequencies above 1 GHz, which are critical for wirelesscommunications technologies. The goal of this project isto provide the microelectronics industry with an accuratemeasurement technique of permittivity for dielectric filmsat microwave frequencies above 1 GHz and to develop afundamental framework to identify the key structural andmolecular attributes that control dielectric properties ofpolymer composites.

Dielectric Metrology forPolymer Composite Filmsin the Microwave Range

Development of the Integrated Passive Device technologyfor high-speed electronics critically depends on the abil-ity to measure the dielectric permittivity and on the abil-ity to control the dielectric properties from the material’smicrostructure. This project provides the microelectron-ics industry with an accurate technique to measure per-mittivity at microwave frequencies and a fundamentalframework to identify the key structural and molecularattributes that control dielectric properties of polymercomposite films.

Jan Obrzut

During the past year we focused on a broadband measure-ments procedure for film substrates that would be suitablefor adaptation as a new industry standard method. Thetest methods currently in use are lumped-element approxi-mations limited to frequencies below a few hundred mega-hertz, especially in the case of high-dielectric constantfilms. Our new broadband measurement methodology isbased on observation and analysis of the fundamentalpropagation mode in a film specimen terminating a coaxialtransmission line. Using this test technique, the imped-ance characteristic and the dielectric permittivity of high-dielectric constant films can be accurately measured atfrequencies from 100 MHz to 10 GHz with the precisionrequired by wireless technologies (Figure 1). To enablemeasurements at frequencies above 20 GHz we are col-laborating with the NIST Radio Frequency Division on fullmode analysis.

In partnership with the IPC Standard Test CommitteeTask Force for Embedded Passive Devices we designedthe standard test protocol and made arrangements withco-sponsoring member companies for round-robinevaluation.

This project also explores the relationships between di-electric properties and structure in polymer resins, blendsand composites. The microwave dielectric properties ofseveral polymer-ferroelectric ceramics composites havebeen evaluated. Microstructural modeling and experimen-tal studies are under way to determine the effect of polariz-ability of the polymer matrix on the apparent dielectricpermittivity of the composite.

Models and measurement techniques developed in thisstudy were identified by a large segment of industrialproducers as being crucial in material design and ing re-ducing the development time of new products.

Figure 1. Broadband impedance data for polymer compos-ite film having permittivity of 34.6 – j 1.6. (a) conventionalresults (b) results calculated for a thin-film capacitance,(c) determined by our new testing procedure .

J. Obrzut, N. Noda, C.K. Chiang, C.L. Soles, D.L. VanderHart (Polymers Division, NIST)

J. Baker, R. Gayer, P. Kabos, B. Riddle (Radio Frequency Technology Division, NIST)

J. Lauffer (IBM), D. Murry (Litton), R. Charbonneau (Storage Tech.), R. Foly (DOD), L.Patch (NCMS), D. McGregor (DuPont), D. Senk (Shipley), R. Sheffield (Nortel), A.Tungare (Motorola), J. Koh (IPC)


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Multiphase Polymeric Materials

The Multiphase Polymeric Materials Program developsrealistic measurement and characterization platforms formultiphase polymeric materials that use a combination ofexperimental measurements and theory and modeling toolsto provide realistic and highly optimized output. Thesemeasurement and characterization tools and platforms areintended to help industries in pre-production evaluation,materials characterization, and performance prediction, aswell as to provide data for process design.

In order to achieve the performance requirements in modu-lus, stiffness, toughness, temperature, chemical and envi-ronmental stability, desired appearance and touch, mostpolymeric materials in use are either phase separatedblends with two or more components, and/or filled withparticles or short/long fibers. The challenge in usingmultiphase polymeric materials extends from processingdesign, through structure and properties prediction andcharacterization, to service life prediction. This program isdesigned to use theoretical and computational modelingtools in conjunction with characterization measurementsto form realistic and workable tool sets.

Specifically, characterization techniques will be developedand used to generate relevant databases or constitutiverelations to be used as input for more realistic theory andmodeling and to bridge the gap in current tools. Currenttheoretical and computational tools are capable of model-ing fine length scales such as nanoscale molecular dynam-ics simulations, microscale self-consistent field or densityfunctional methods, and meso-scale time dependent

Ginsburg-Landau or Cahn-Hilliard-Cook techniques. Onthe other hand, macroscopic part sized finite-element-flowcalculations and Object Oriented Finite element analysis(OOF) for properties calculations and virtual testing aremuch coarser grained tools. A seamless connection be-tween these two sets of computer tools is not available toprovide realistic materials properties for design, predictionand characterization.

This program is working currently on three materials char-acterization projects to provide:

(1) phase separation/crystallization results together withinterfacial characterization and rheological data to formconstitutive relations as input for finite-element-flow mod-eling, and characterization of phase structure;

(2) structure, dynamics, and modulus characterization inhigh surface area particle-filled polymers and blends forperformance characterization and validation of multiscalecomputer modeling; and

(3) fiber tow characterization and failure results as input tofinite-element-based mechanics and performance evalua-tion. All three projects are linked to future applications ofOOF to polymer research on property prediction and vir-tual testing.

MSEL researchers work with industrial partners throughinformal collaborations, Cooperative Research and Devel-opment Agreements (CRADAs), and consortium arrange-ments. Industrial partners include resin suppliers, systemsuppliers, parts producers, members of the automotiveindustry, and offshore oil platform companies.

Charles C. Han


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Constitutive Relationshipof Polymer Blends forProcess Modeling Needs

Howard Wang, Charles C. Han

H. Wang, C.C. Han, K. Shimizu, G.Z.G. Wang, H. Kim, E.K. Hobbie (Polymers Divi-sion, NIST)

B.S. Hsiao (SUNY), D. Lohse (EXXON)

The first stage of this project is to obtain detailed and quan-titative understanding of the phase transitions in apolyolefin blend. Then the focus will shift to the dynamicsof phase separation in the presence of crystallization andnon-equilibrium phase behavior under shear flow. A pair ofcommercial olefin polymers, metallocene-catalyst synthe-sized statistical copolymers of ethylene/hexene (PEH) andethylene/butene (PEB), were selected as model materials.The PEH component is crystallizable. Research on themodel system results in the following findings:

Measurement of Phase Transitions

Modified optical techniques were used to identify theboundary of liquid-liquid phase separation (LLPS) becausethe almost identical refractive index of the blends compo-nents and slow kinetics made conventional optical methodsdifficult. The LLPS boundary has been determined usingcrystallization induced contrast. Incoherent and coherentlight scattering, light transmission, atomic force microscopy(AFM) and differential scanning calorimetry, are used toexploit the crystallization morphology from previously ho-mogenous or segregated blends. The blend exhibits anupper critical solution temperature of 146 oC. The composi-tion dependence of the LLPS boundary follows the predic-tion of Flory-Huggins theory for binary polymer mixtures.The equilibrium melting temperature of the blends decreasesfrom 145 oC for pure PEH with increasing PEB concentrationin the miscible phase, whereas it remains relatively constantwithin 2-phase region (figure left).

Process modeling may facilitate design of optimal condi-tions for processing polymer blends provided that thecomplex structure and behavior of these materials aretreated adequately. Techniques and methodologies aredeveloped to define and characterize necessary rheologi-cal, morphological and interfacial properties for multi-phase polymer blends as a function of processing param-eters, composition, phase miscibility, and crystallinestructure growth. Constitutive relationships are formu-lated either as a database or in combination with ana-lytical expressions for process modeling needs.

Competing Kinetics

The kinetic interplay between crystallization and phaseseparation in a polymer blend has been examined. Bycontrolling the relative quench depths for liquid-liquidphase separation and crystallization, the growth kineticsof the characteristic length scales of the simultaneousordering processes show a crossover from crystallizationdominated to phase-separation dominated behavior. Basedon a scaling argument for late-stage spinodal decomposi-tion, we conclude that this kinetic crossover is inevitablein a blend for which the critical temperature of liquid-liquidphase separation is above the equilibrium melting tempera-ture of the blend, as shown in the figure below.

Crystallization Morphology

Morphology development during competing LLPS andcrystallization, and during crystallization in a previouslysegregated blend, either under quiescent conditions orunder shear flow, is investigated using time-resolvedsmall-angle light scattering, time-resolved small- and wide-angle x-ray scattering (SAXS and WAXS), optical micros-copy (OM), and AFM. To date, comprehensive OM,SAXS and WAXS measurements on pure PEH and criticalblends at different isothermal temperatures have beencompleted. AFM measurements on crystal morphology atselected temperatures are also made.


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We currently are engaged in a project to predict the micro-structure that forms during the injection molding of poly-mer blends. Blend mixtures usually enter an injection mold-ing cavity, well mixed and quenched, from an extruder.However, upon entering the cavity, the drops are highlysheared and break-up into finer and finer sizes near moldwalls, and coarsen towards equilibrium sizes in regions oflow shear. This leads to a non-uniform “skin-core” micro-structure in the final part, which highly affects the proper-ties. In order to predict the properties, one must be able tomodel the morphology that develops during flow. Ourapproach to this problem involves modeling flow at sev-eral length scales. Microscale models which simulatemultiphase flow are used to predict detailed drop morphol-ogy. However, such models are too computationally de-manding to model an entire injection molding process.Thus, volume averaged macroscale models, which usephase-averaged materials properties and micromodels topredict average material structure, are used to predict moldfilling. By using such models in tandem, one can get agood approximate picture of the drop morphology.Complementing model development, experimental work

Modeling of Interfacesand Interphases ofPolymeric Systems

Frederick R. Phelan Jr., Erik K. Hobbie,Charles C. Han

A computational software tool is developed for predictingthe microstructure evolution of polymer blends in injec-tion molding operations for industrial users. The injectionmolding of polymer blends is carried out generally whilethe components are phase separated in which drops ofone phase are dispersed in a matrix phase. The detailedmorphology that develops during flow depends on thefluid mechanical deformation history, component rheo-logical properties, and blend thermodynamics. The utilityof the computational method is enhanced through a fun-damental understanding of the interplay between thevarious process parameters and blend microstructure.

provides viscosity and drop size measurements as a func-tion of shear rate and composition in blend mixtures.

Progress in modeling microstructure evolution resultedfrom a microflow simulation for binary mixtures based onthe multiphase momentum balance and a Ginzburg-Landaufree energy for the chemical potential in the chemical spe-cies balance. The model equations are solved together withthe continuity equations, using a spectral finite elementmethod. Figure 1 shows the evolution of a randomly dis-persed initial phase into a discrete layered structure duringshear flow. In the absence of flow the initial state coarsensinto discrete drops. The simulation shall be extended tonon-Newtonian flows in the next phase of the work.

An experimental component of this project is an exhaustiverheo-optical study of a variety of polymer blend systemsunder simple shear flow. By varying such parameters as theviscoelasticity of the components, the proximity to a criticalpoint, and the interfacial tension between the phases, weare accumulating an experimental database to help guidethese simulations. The primary measurement techniques arelight scattering, optical microscopy and rheometry.

F.R. Phelan Jr., E.K. Hobbie, H. Wang, C.C. Han (Polymers Division, NIST)

T. Nguyen (Building and Fire Research Laboratory, NIST)

S. Glotzer (University of Michigan), Polymer Interphase Consortium (NIST, DowChemical, PPG, Visteon)

Figure 1. Evolution of binary microstructure during shear flow. (Left) Initial condition: randomly dispersed two-phasestructure. (Right) Near steady state under shear flow, the phases form a layered structure.


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Shear-induced structural ordering in materials containingclay is a new problem encountered in nanocomposite-based materials. The shear orientation of viscoelasticpolymer-clay solutions was studied by means of rheology,flow birefringence and small-angle neutron scattering(SANS) under shear. The polymer chains are in dynamicadsorption/desorption equilibrium with the clay particlesto form a “network”. The elastic behavior of the networkwas characterized by constant stress, oscillatory shear,and stress relaxation experiments. Experiments understeady flow characterized the transient behavior of thenetwork. With increasing steady shear rate a pronouncedminimum in birefringence was observed at a critical shearrate showing that clay platelets orient first, then polymerchains start to stretch. The shear rate dependent viscosityexhibited near power-law behavior and no correspondingcritical feature. While birefringence detects orientationaleffects on a microscopic-length scale, rheology averagesover macroscopic changes in the sample. The same degreeof orientation could be achieved under constant shear rateor constant stress conditions.

Simulations of a polymer melt surrounding a symmetricnano-particle have already shown the important role playedby nano-particle/polymer interactions on the changes in thestructure, dynamics, and glass transition of the melt. Con-tinued work on these systems shows the importance ofchanges in the surface goemetry and the surface-to-volumeratio on the relaxation of chains near the surface. Simula-tions focused on larger systems are probing the role inter-actions play in the dynamic clustering and dispersion ofnano-particles within the melt. Our results indicate thatclustering is very sensitive to changes of both the particle/particle and particle/polymer interactions. Additionally,shear flow, such as that experienced during injection mold-ing, can alter the clustering properties of the particles.Finally, these particles also alter the blend phase diagram,an area of future consideration. Separately, we have alsoundertaken simulations of a carbon nanotube filled polymermelt in an effort to explore changes introduced by fillerasymmetry.

Synergistic Interactionsin Polymer-NanoparticleComposites

Inorganic fillers frequently are used to enhance polymerproperties. New attributes may be achieved withnanoparticulates provided that the underlying science isdeveloped. Polymer nanocomposites are important inmany diverse industrial processes. Potential applicationsderived from synergistic behaviors and hybrid propertiesof polymer-nanoparticle composites include data storageand optical and electro-rheological materials for displaydevices. The objectives of this project are to set new direc-tions and provide fundamental understanding of polymer-nanoparticle interactions and how they dictate the prop-erties of different materials.

Gudrun Schmidt, Francis W. Starr,Erik K. Hobbie, Charles C. Han

Figure 1. Concentration dependence of SANS intensityfrom polymer-clay nanocomposite samples is correlatedwith AFM. LRD2-bulk (40% PEO, 60% clay) and LRD5-bulk (63 percent PEO, 37 percent clay).

Figure 2. Snapshot of molecular dynamics simulationshowing a configuration of dispersed nano-fillers embed-ded in polymer melt.

G. Schmidt, F.W. Starr, E.K. Hobbie, C.C. Han (Polymers Division, NIST)


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To achieve the goals of the project, research is conducted inthree tasks. First, techniques are developed to characterizethe microstructural features in complex multicomponentpolymeric systems. Second, existing measurement tech-niques are adapted or new methods are generated to deter-mine properties in materials with complex microstructure.Finally, models are formulated to relate the performance ofsuch materials to the properties of their constituents andthe microstructure that is present. Where appropriate, Ob-ject Oriented Finite Element Analysis (OOF) is employed toincorporate the measured microstructure into the models.The methods developed in the three tasks then are appliedto model systems that are relevant to industrial needs.

Hybrids are polymers reinforced with two or more differenttypes of continuous fibers. By combining two fibers it isoften possible to achieve significantly better trade-offsamong various properties and between cost and perfor-mance. For this reason, hybrids are a prime candidate foruse by the construction industry in composite bridge de-sign and by the oil industry in off-shore drilling platforms.NIST is working with the Composites Engineering andApplications Center at the University of Houston to bridgethe gap between laboratory tests and industrial applica-tions. Recent results in this program are discussed below.

Structure-PropertyCharacterization andModeling

The goal of this project is to provide industry test meth-ods, reference data, and predictive models for advancedpolymeric material by understanding the role of micro-structure in performance. This technology will enablefabricators and users of these materials to develop supe-rior products for applications in transportation, infra-structure, aerospace, and off-shore oil exploration.

Microstructure Determination: Microscopy has been usedto determine fiber arrangement, void content, and voiddistribution in hybrid composites, but fiber concentrationand mix are difficult to quantify. Consequently, a modifica-tion to the burn-off test was developed to assess thesefeatures. The procedure has been verified with tests onsamples of known concentrations (see figure left).

Test Method Development: The Iosipescu test was used tomeasure the shear moduli of hybrid composites. This testhas now been used to characterize the behavior of themodel hybrid composites that were characterized in theMicrostructure Determination task. Tensile properties werealso determined.

Modeling: To predict the moduli determined above, a tow-based finite element model was developed. Based on prop-erties of the constituents, both the tensile and shear moduliwere modeled successfully as shown in above figure. Theactual microstructures determined in the MicrostructureDetermination Task were used in the model. The work isnow being extended to failure behavior. With a tow-basedapproach, the complete stress strain curve for this samplecould be predicted based on the behavior of a single glassand a single carbon fiber.

Donald L. Hunston, Charles C. Han

D.L. Hunston, W.G. McDonough, J. He, M. Chiang, C.C. Han (Polymers Division,NIST)

Lincoln Composites, OSI, Owens Corning, Composites Engineering and Applica-tion Center, Cornell University


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42

It is recognized that single fiber tests are inadequate inpredicting failure in 3-dimensional structures. Our effortsare transitioning from 2-D multi-fiber arrays to 3-D fiberarrays. The current data, however, focuses only on 2-Dmulti-fiber model composites.

In Figure 1, the inter-fiber spacings between four of the fivefibers in a 2-D array are between (1.4 to 1.5) fiber diameters.Capitalizing on optical coherence tomography’s (OCT’s)unique ability to see changes in matrix stresses, the areaimmediately surrounding the fibers (> 2 fiber diameters) wasobserved to have a different intensity than the bulk resin(< 2 fiber diameters). This intensity change reflects theresidual curing stresses that occur due to the close proxim-ity of the fibers. This change in intensity is not observed insingle-fiber fragmentation specimens.

Mechanics of Fiber andNano-Filled Composites

Gale A. Holmes, Charles C. Han

Failure prediction is critical to the use of fiber-reinforcedcomposites in many applications. Multi-fiber model com-posites are being used to conduct fundamental studiesinto the nucleation of failure in fibrous composites. Cur-rent results have revealed that the nucleation of criticalflaws in unidirectional fibrous composites may dependon the time-dependent redistribution of stress by theviscoelastic matrix. Although their role in flaw nucle-ation is not understood clearly, shear deformation bandshave been detected between fiber breaks and residualcuring stresses have been detected in the matrix by opti-cal coherence tomography.

Consistent with epoxy-compatible industrial coatings, the11-AUTCS coating exhibits matrix crack formation in addi-tion to fiber-matrix debonding during fiber fracture. Initialinvestigations revealed the presence of 45o shear deforma-tion bands emanating from the crack tips when specimensare under tensile load (see Figure 2). The shape of thematrix cracks surrounding each fiber break is similar to un-symmetrical penny-shaped cracks. It is known that penny-shaped cracks in a material subjected to uniaxial tensileloads generate 45o deformation shear bands that form rela-tive to the tensile axis at the crack-tip. The deformationbands emanating from the crack tips in Figure 2 may relateto this phenomenon. The location of the penny-shapedflaws within the composite is controlled by the spatialpopulation of flaws in the embedded fiber and the stresstransfer efficiency at the fiber-matrix interface. The influenceof these shear bands on the non-aligned fiber break pat-terns shown in the figure is not known. It is believed at thispoint that these bands may be an important key to under-standing the role that the viscoelastic matrix plays in nucle-ating critical flaws in fibrous composites.

G.A. Holmes, C.C. Han, W.G. McDonough, J.P. Dunkers, E.B. Feresenbet (PolymersDivision, NIST)

L. Phoenix (Cornell University), D. Raghavan (Howard University), J. Nairn(University of Utah), Eric Pohl (Witco Chemicals)

Figure 1. Isosurface plot of a multiple E-glass fibers (blue)embedded in DGEBA/m-PDA matrix (red). Green regionsurrounding the fibers denotes residual curing stresses.Data obtained using optical coherence tomography.

The initial 2-D multi-fiber arrays consisted of embeddedfibers coated with 11-aminoundecyl trichlorosilane (11-AUTCS) deposited using self-assembled monolayer (SAM)technology. The SAM technology is being used in acompanion micromechanics project to probe the effect ofcovalent bonding, mechanical interlocking, and physico-chemical interactions on the transfer of shear stresses atthe fiber-matrix interface.

Figure 2. Fiber break patterns from E-glass/DGEBA/m-PDA 2-D multi-fiber array (stressed). The interfiberspacing is denoted by φφφφφ.


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Most polymer blends exhibit a phaseseparation that leads to a heteroge-neous morphology. The scale andtype of the morphology determinesthe properties of the polymer blend.However, understanding the relationbetween the morphology and theproperties of polymer blends is stilllacking. In order to explore this rela-tion, we performed computationalstudies that combine simulation ofphase separation with generic finiteelement approach through a computerprogram having the capability ofmorphology adaptation. This combi-nation of modeling can help to identify the potentials ofmultiphase material behavior and can serve as a virtualexperimental tool. This tool allows scientists to explorebehavior on the scale of the microstructure and to com-pare that behavior with macroscopic properties. Conse-quently, it can result in reduced material fabrication costsand improved material performance. Currently, our studyhas been limited to binary polymer blends.

Poly-OOF: A VirtualExperimental Tool forPolymer Research

The understanding of the relation between the morphol-ogy and properties of a polymer mixture is still lacking.Our objective is to develop a morphology-adaptive ap-proach that allows scientists and engineers to explorethe behavior on the scale of the microstructure and com-pare that behavior to macroscopic properties.

Martin Y.M. Chiang, Charles C. Han

The procedure of the virtual experiment is illustrated inFigure 1. The phase separation of polymer blends is simu-lated using a Cahn-Hilliard-Cook model solved with a finitedifference scheme. The micrograph of the simulated mor-phology is automatically adapted through NIST-devel-oped OOF (Object-Oriented Finite Element Program),which converts the information describing the microstruc-ture into a finite element mesh (Figure 2). The resultingmesh is used by a general-purpose finite element program(Abaqus) to formulate a mathematical model of the physi-cal system subjected to virtual external influences. Thematerial properties of the blends can then be calculatedand the response visualized to explore the interaction ofthe components. To date, the elastic modulus and coeffi-cient of thermal expansion have been predicted for a rangeof simulated microstructures of a phase-separated binarysystem. Three combinations of material models have beenconsidered that correspond to glassy-glassy, rubbery-rubbery, and glassy-rubbery states of the components ofthe system.

M.Y.M. Chiang, N. Parekh, S. Glotzer, J. He, C.C. Han (Polymers Division, NIST)

Center for Theoretical and Computational Material Science, NIST

Figure 1. Flow chart of the proposed FEA as a virtualexperimental tool.

Figure 2. Micrograph of simulated morphology and finiteelement mesh.

Cahn-Hilliard-Cook Model to Predict Phase

Separation

Preprocessorof OOF

(ppm2oof)

CreateABAQUSInput File

(oof2abaqus)

ABAQUSPreprocessor(Finalization)

Mathematical Model of Physical Systems Subjected to Virtual

External Influences

Visualize the Response and Predict Physical Properties

ABAQUSPreprocessor(Finalization)

Mathematical Model of Physical Systems Subjected to Virtual

External Influences

Visualize the Response and Predict Physical Properties

Prediction of Properties

(Finite Element)

Prediction of Phase Separation

(Finite Difference)

OOF Prediction of Properties

(Finite Element)

Prediction of Phase Separation

(Finite Difference)

OOF

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Polymer Characterization

The Polymer Characterization Program provides measure-ment methods, data, and Standard Reference Materials(SRMs) needed by U.S. industry, research laboratories, andother federal agencies to characterize rheological and me-chanical properties of polymers, their processibility andperformance, and to improve process control. In responseto the critical needs of industry for in-situ measurementmethodologies, a substantial effort is under way to developoptical, dielectric and ultrasonic probes for use in extrusionand injection molding. Improved methods for determiningmolecular mass distribution of polymers are developedowing to the dramatic effect it has on processibility andproperties. Mechanical properties and performance aresignificantly affected by the solid-state structure formedduring processing. Importantly, unlike many other commonengineering materials, polymers exhibit mechanical proper-ties with time dependent viscoelastic behaviors. As a re-sult, the program also focuses on techniques that measurethe solid-state structure and rheological behavior of poly-meric materials.

Chromatographic techniques, which require calibration bystandards of known molecular mass, are the principal meth-ods for determining molecular mass distribution. Becausecalibration standards are lacking for most polymers, crudeapproximations must be used to interpret chromatographicdata. Recent program activities exploit advances in massspectrometry using matrix-assisted laser desorption ioniza-tion to develop the method as a primary tool for the deter-mination of the molecular masses of synthetic polymers,with particular emphasis on commercially importantpolyolefins. Advances are sought in measurements of thesolid-state structure of polymers, including optical coher-

ent tomography, inelastic neutron scattering, and sumfrequency generation spectroscopy.

The extrusion visualization facility combines in-line micros-copy and light scattering for the study of polymer blends,extrusion instabilities, and the action of additives. Currentresearch focuses on understanding and controlling the“sharkskin instability” in polymer extrusion. Fluorescencetechniques are developed to measure critical process pa-rameters, such as polymer temperature and orientation thatwere hitherto inaccessible. These measurements arecarried out in close collaboration with interested industrialpartners.

The polymer industry and standards organizations assist inthe identification of current needs for SRMs. Based onthese needs, research on characterization methods andmeasurements are conducted leading to the certification ofSRMs. Molecular standards are used primarily for calibra-tion of gel permeation chromatographs, the principalmethod employed by industry for assessing molecularmass and molecular mass distributions. Melt flow stan-dards are used in the calibration of instruments used todetermine processing conditions for thermoplastics. Non-Newtonian rheological standards are also developed toexhibit the typical polymeric behaviors of shear thinningand normal stresses; these standards are also used forcalibration of rheological instruments and for research intoimproved measurement methods. Reference biomaterialsare produced for test method harmonization, assessment ofnew materials, and generation of reference data.

Contact Information: Bruno M. Fanconi


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Optical coherence tomography (OCT) is a non-invasive,non-contact optical imaging technique that allows thevisualization of microstructure within bulk materials. OCTuses a near-infrared low coherence source and a scanningfiber optic interferometer for depth discrimination. Reflec-tions generated from material heterogeneity are collected asa function of depth. A requirement for this type of tomogra-phy is that the material be transparent to near infrared light,

Optical CoherenceTomography

We have adapted optical coherence tomography (OCT),a new method for medical imaging, to the realm of mate-rial science. More specifically, we apply OCT for meso-scale, volumetric characterization of polymer composites,birefringence, polymer blends, biomaterials and ceramiccoatings that cannot be obtained by any other technique.A volumetric representation of the internal structure ofthe above materials in the micrometer- to millimeter-sizescale is often required to understand how various prop-erties of interest are interrelated.

polarization sensitive (PS-OCT) and these systems gatherinformation about sample birefringence.

OCT has been used historically for medical imaging. We arebridging the gap between materials science and medicine byusing OCT to non-destructively elucidate the meso-scalestructure of heterogeneous polymeric systems, includingbiomaterials and polymeric composites. An advantage ofOCT is the ability to image biomaterials, such as tissue engi-neering products, in aqueous medium to mimic their naturalstate. Critical characterization challenges in tissue engineer-ing scaffolds are to quantify pore size, size distribution andtortuosity and to relate these variables to some measure ofthe success of cell growth. By generating scaffolds withsystematic variations in pore size and pore connectivity, cellgrowth can be studied quantitatively. In this work, samplesmade of polycaprolactone and poly(ethylene oxide), PEO,blends were annealed to various times at 75 °C. Then, thePEO phase was removed by dissolving in water. Pore sizedistribution and tortuosity of these materials were obtainedsuccessfully from OCT results. Given the success of thisinitial work, the next phase of this project will consist ofrelating the cell growth to the 3-D pore structure of scaffoldsgenerated with systematically varying microstructure.

Two issues in the area of composites were addressed usingOCT. Reinforcement microstructure affects the success of acomposite part during the manufacturing process. OCT wasused to image the reinforcement microstructure and therebyprovide insight into the flow characteristics of the resininside the mold. Secondly, OCT was used to identify variousdamage modes within a glass-reinforced composite. Anexample is given in the figure where the breaks along theglass fiber are marked by the arrows. The birefringence inthe polymer matrix surrounding the breaks is responsiblefor the optical contrast. In the near future our OCT systemwill be upgraded to include a polarization sensitive capabili-ty. Effort will be directed to quantify birefringence in 3-D. Inaddition, data dropout from sample birefringence will becompensated for, to provide an increased imagedepth in deformed samples.

making many polymer systems excellent candidates. Theimaging is performed by collecting back-reflected lightgenerated from heterogeneities within the sample. Thehigher the refractive index mismatch at a boundary, thestronger the return reflection at any given depth. Thus,OCT has the ability to distinguish different types of fea-tures. OCT is attractive because of its high sensitivity,which enables a typical sample to be imaged at depthsanywhere from 0.5 mm to 4 mm. The resolution of the sys-tem is 10 µm to 20 µm. Recently, resolutions of 3 µm havebeen reached with state-of-the-art lasers, electronics andoptics. Additionally, OCT systems have been built that are

G.A. Holmes, W.G. McDonough, M.Y. Chiang, N.R. Washburn, A. Karim (PolymersDivision, NIST)

T. Griffin (Information Technology Laboratory, NIST)

An OCT image of the multiple breaks of a glass fiberembedded in polymer matrix. The breaks in the fiberbecome visible in OCT through the stress-induced bire-fringence of the matrix material. The locations of thebreaks are marked by arrows in the figure.

Joy P. Dunkers


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New methods of traditional metal cationization on fullysaturated polyethylenes are explored in collaboration withProfessor Liang Li of the University of Alberta. In this work,silver is used as the metal cation as is typical for syntheticpolymer mass spectrometry; however, instead of using theusual organic acid matrices finely divided cobalt powder issubstituted. Mass spectra of intact oligomers up to 5000 uhave been measured, indicating intact parent in cationi-zation by silver is possible; however, fragmentation ions arealways present complicating spectral interpretation. It iswell-known that most metal ions will insert into C-C bondsleading to fragmentation on the time scale of the experiment.

A chemical modification method has been developed in thePolymers Division that allows mass spectrometry to beperformed on saturated hydrocarbon polymers. Two syn-thetic steps are involved: selective bromination of the poly-mer, followed by conversion of the brominated site to acharged ammonium or phosphonium group. A strong massspectrum was produced from the modified polymers whilethe unmodified and the brominated polymers produced nosignal at all. This concept has been termed the “covalentcationization method” and has also been demonstrated onunsaturated olefins such as polystyrene and polybutadiene.It is envisioned that this method may become applicable toall types of polymers complementing, or possibly replacing,the metal cationization methods already in use.

Physical ionization methods are also considered. Removalof valence electrons by electron or photon irradiation typi-cally results in excess energy imparting to the molecule andsubsequent scission of the C-C bonds. This leads to anabundance of fragment ions. Working with Daniel Fischer(Ceramics Division) using the NIST vacuum-ultravioletbeamline U7A at the National Synchrotron Light Source atBrookhaven National Laboratory (Upton, N.Y.) carbon coreelectrons were ejected from gas-phase alkanes. The photonenergy can be tuned to promote Auger relaxations from theC-H bonds and not from the C-C bonds to avoid chainfragmentation. Figure 1 shows a comparison of core-levelphotoionization and electron-impact ionization for propane.

Polyolefin MassSpectrometry

William E. Wallace

Saturated hydrocarbon polymers, polyethylene andpolypropylene, are the most widely used of all syntheticpolymers. Their molecular-mass distribution (MMD) iscritical in determining performance properties.Mass spec-trometry is currently the most promising method for ob-taining accurate, absolute MMDs; however, polyethyleneand other polyolefins have not been amenable to massspectrometric characterization due to the ineffectivenessof conventional methods of cationization. The PolymersDivision has addressed this challenge with three distinctcationization approaches: traditional metal cationi-zation, chemical modification, and physical ionization.

The photoionization does bias the mass spectrum towardproton loss compared to the electron-impact ionization;however, residual vibrational energy in the room tempera-ture propane combined with overlap in the valence-electron orbitals leads to not insignificant C-C bondscission.

W.E. Wallace, C.M. Guttman, B.M. Fanconi, B.J. Bauer, S. Lin-Gibson, L. Brunner,D.L. Vanderhart, W.L. Wu, W.R. Blair (Polymers Division, NIST)

D.A. Fischer (Ceramics Division, NIST)

L. Li, T. Yalcin, R. Chen (University of Alberta)

Figure 1. Comparison of core-level photoionization with287.5 eV photons ( C 1s →→→→→ C-H σσσσσ* transition) andelectron-impact ionization with 70 eV electrons for pro-pane. The parent ion at 44 u is seen in both spectra. Thecore-level photoionization is dominated by ions at 38 u to40 u created by the loss of hydrogen atoms while theelectron-impact ionization is dominated by C-C bondcleavage as evident from a major peak at 29 u correspond-ing to C2H5

+.

Industry Interaction:

Discussion of measurement needs and future collabora-tions on polyolefins with Dow Chemical, ExxonMobile,and Union Carbide is in progress.


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Fluorescent sub-micrometer probe molecules are needed tocharacterize structures and transport properties of mem-branes, polymer blends and biomaterials. An ideal fluores-cent probe would exhibit monodisperse size, versatile solu-bility, high luminescence, minimal photobleaching, andstability under conditions of varying temperature, solventand pH. Taken together, these criteria are rather demandingmaking the development of model probes a challenge.

With the goal of fluorescent probes inmind, we prepared and characterized anew class of highly branched, star-shaped polymers containing fluores-cent tags. These stars have well-defined structures with effective solu-tion-phase diameters on the order of10–100 nm (0.01–0.1µm). The stars canbe tagged with either an organicfluorophore or with fluorescent semi-conductor nanocrystals (“quantumdots”). The attractive features of thesenovel probes include controllablepolymer architecture and tunablephotophysical properties.

number of arms contain unreacted primary amine end-groups, which function as reactive sites for the attachmentof organic dyes. The labeled stars are highly luminescentand color-tunable, but organic fluorophores often exhibitpoor resistance to photobleaching.

Semiconductor nanocrystals, such as CdS or CdSe, are analternative type of photobleach-resistant fluorescent

marker. PAMAM dendrimers interactstrongly with many types of metalions, including Cd2+, allowing attach-ment of CdS nano-crystals to thestar polymer cores. We have pre-pared successfully highly fluores-cent star-CdS nanocomposites andcharacterized their physical proper-ties. Gel permeation chromatographyand small-angle neutron scatteringexperiments indicate that the CdSnanocrystals may be introducedwithout disturbing the size distribu-tion of the stars. Although it has notbeen straightforward to achievecolor tunability, these materials are a

FluorescentSub-Micrometer ProbeMolecules with StarlikeArchitecture

Ronald C. Hedden, Barry J. Bauer

Rapid advances in nanostructured materials technologymotivate development of new methods for stuctural char-acterization. We are developing fluorescent polymericmarkers for use as probes of sub-micrometer features inmembranes, polymer blends and biomaterials. Fluores-cent star-shaped polymers with effective sizes in the10–100 nm range have been targeted as model probes.The detection of fluorescent probes using advancedoptical techniques could lead to new methods in polymerstructural characterization.

R.C. Hedden, B.J. Bauer (Polymers Division, NIST)C. Muzny (Chemical Sciences and Technology Laboratory, NIST, Boulder)

F. Gröhn (Max-Planck-Institut für Polymerforschung, Mainz, Germany)

Figure 1. Schematic diagram of a novelfluorescent probe: dendrimer-star poly-mer containing a CdS nanocrystal.

Stars are prepared by attachment ofmonofunctional poly(ethylene glycol)(PEG) “arms” to poly(amidoamine)(PAMAM) dendrimer “cores”.Dendrimers are layered, treelike polymers that containmany functional endgroups. The number of dendrimerendgroups increases geometrically with the dendrimer“generation,” or number of layers. The maximum numberof PEG arms that may be attached is equal to the numberof dendrimer endgroups. A PAMAM Generation 4 starmay have up to 64 arms, and a PAMAM Generation 7 starmay have up to 512, for example. PEG was chosen for the“arms” due to its versatile miscibility with water, organicsolvents and many polymers.

Using a standard synthesis, we have labeled the stars withorganic fluorophores. Stars with less than the maximum

milestone in the development ofphotobleach-resistant fluorescentprobes.

Current work focuses on testingfluorescent star polymers as probes. Researchers at NIST(Boulder) are characterizing mass transport in membranesby novel combinatorial methods using fluorescent probes.To facilitate this study, we are developing a series of fluo-rescent stars with well-defined sizes and independentemission spectra. We are also interested in observing thebehavior of the stars in immiscible polymer blends usingadvanced optical microscopy techniques. We will deter-mine whether the stars migrate to phase boundaries tohelp explain how highly branched polymers affect theproperties of immiscible blends.


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Standard Reference Materials and Reference Materials areissued to address needs of the producers, processors andusers of polymers for calibration and for performanceevaluation of instruments used in the control of the syn-thesis and processing of polymers, as well as benchmarksfor comparisons of measurement methods and develop-ment of new materials. Recently produced Standard Refer-ence Materials include polyethylene of narrow mass distri-bution certified for mass average molecular mass andintrinsic viscosity and a nonlinear fluid standard for rheo-logical measurements. In addition, the first reference bio-material, RM 8456, an orthopedic grade ultra-high molecu-lar weight polyethylene, UHMWPE, was issued for use indevelopment of improved test methods for wear and as abenchmark for development of improved materials. Radia-tion cross-linking of UHMWPE is being pursued by theorthopedics products industry for improved wear resis-tance products. Better test methods for degree of cross-linking are under evaluation by ASTM throughinterlaboratory comparison on irradiated samples pro-duced from RM 8456. NIST participated by providingspecimens of RM 8456 in a form suitable for theinterlaboratory comparison. In anticipation of continuingneed for Reference Material UHMWPE for radiation stud-ies NIST is issuing orthopedic grade UHMWPE cubes forradiation cross-linking tests and analysis. This ReferenceMaterial is produced from RM 8456.

Among polymer standards provided by NIST are thosecertified for melt flow, the primary characteristic of a poly-mer melt used by both producers and processors of poly-mers to determine the required characteristics of process-ing equipment. The NIST melt flow standards arereferenced in ASTM test method for melt flow for use inassessing laboratory proficiency. Stock of SRM 1473, amelt flow standard, will be depleted in a few months. Toaddress the continuing need for this standard a new batchof resin, from the same source as that used to produceSRM 1473, is certified for melt flow. Current standard testmethod for melt flow extends to temperatures and flow

Standard ReferenceMaterials

Charles M. Guttman, Carl R. Schultheisz

Reference Materials (RM) and Standard Reference Mate-rials (SRM) are produced to address needs of the produc-ers, processors and users of synthetic polymers for calibra-tion of instruments, assessment of laboratory proficiency,test method development and materials development. Anorthopedic grade ultra-high molecular weight polyethyl-ene RM is prepared in the form of cubes for irradiationstudies. Recertification of a melt flow standard and certifi-cation of a non-Newtonian fluid for rheological propertiesassist polymer processors and producers. The first polymermolecular mass standard is produced with the completemass spectrum as ancillary data.

rates under which polymer melts typically degrade,thereby affecting the reliability of the result. Test condi-tions are determined under which a thermally stabilizedresin would have sufficient stability to render melt flowmeasurements more meaningful. A high temperature, highflow rate melt flow standard would be used for perfor-mance evaluation under these conditions.

SRM 2490, a non-Newtonian polymer solution for rheo-logical measurements, was issued for use in calibrationand performance evaluation of instruments used to deter-mine viscosity and first normal stress difference in steadyshear, or to determine the dynamic mechanical storage andloss moduli and shift factors through time-temperaturesuperposition. Discussions with potential customers ofSRM 2490 revealed the need for a second non-Newtonianfluid designed for calibration and performance evaluationof rheometers that lack the stringent temperature controlrequired for calibration with SRM 2490. A suitable polymerfluid, poly (dimethylsiloxane), has been procured to meetthese requirements. We will conduct homogeneity mea-surements followed by certification for non-Newtonianviscosity and the first normal stress difference over arange of temperatures and shear.

SRM 2888, polystyrene possessing a narrow molecularmass distribution, is certified for mass average molecularmass by light scattering. The number average molecularmass determined by high-resolution NMR and mass spec-trum measured by matrix-assisted laser desorption/ioniza-tion (MALDI) mass spectrometry (MS) are provided asancillary data. This material was used in an interlaboratorycomparison of mass distribution measurement by MALDIMS. The results of the analysis of data submitted by the18 participating laboratories were published in the journalAnalytical Chemistry (Anal. Chem. 2001, 73 1252-1262).Additional information on the interlaboratory comparisonis given in the accomplishment section of this reportunder the title “Polymer Mass Distribution by MassSpectrometry.”

C.M. Guttman, C.R. Schultheisz, J.A. Tesk, W.R. Blair, D.L.VanderHart, B.M. Fanconi,W.E. Wallace, S.J. Wetzel, R. Goldschmidt (Polymers Division, NIST)

Interlaboratory Comparison, Industrial Participants: Lab Connections, EastmanChemicals, Air Products, 3M, ICI, Charles Evans & Associates, Hercules, BrukerDaltonics, Zeneca, Union Carbide, DuPont


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Sample Preparation

For synthetic polymers samples, MALDI TOF MS can yieldquantitative information about end groups, repeat units,molecular masses and molecular mass distributions. Accu-rate quantitative measurements require equimolar re-sponses for all sample species in the mass range overwhich a sample is distributed.

Efforts to modify MALDI sample preparation techniquesfor synthetic polymers with the goal of increasing samplehomogeneity and the equimolar peak signal intensity havemet with modest success. The usual sample preparationmethod involves hand-depositing on the sample plate. Thissample preparation technique leads to variations in MALDIsignal intensity as the ablating laser beam scans across thesample, indicating sample inhomogeneities on the size ofthe laser spot (25 µm). An electrospray sample preparationtechnique showed improvement in the statistical variationof MALDI intensities as long as the sprayed coating wasthick.

Experiments were conducted also to address sample mor-phology in the nanometer scale with the goal of determin-ing if optimal MALDI signal was obtained when analytemolecules were molecularly dispersed in the matrix. Thisquestion derives from the premise that the lack of MALDIsignals from polyolefins may relate to their segregationfrom the matrix owing to rapid crystallization under thesample preparation conditions used. Small-angle neutronscattering has been used to measure the size and level ofdispersion of synthetic polymers in MALDI samples pre-pared by electrospraying. In dithranol, a common matrix,deuterated polystyrene (PSD) was found by SANS to formaggregates of size greater than 20 nm. The size of the aggre-gates appears to be unaffected by the solution concentra-tion of PSD in sample preparation, at least over the concen-tration range typically used. This suggests thatreproducible MALDI results may be obtained withoutmolecularly dispersed polymers.

Quantitative MassSpectrometry ofSynthetic Polymers

Charles M. Guttman

The molecular mass distribution (MMD) of a polymer hasprofound effects on how it is processed and the resultantproperties. Recent advances in matrix-assisted laserdesorption/ionization (MALDI) time-of-flight (TOF) massspectrometry (MS) suggest that it is possible to obtainthe MMD of undegraded polymer molecules with molecu-lar masses up to 300,000 g/mol. Experiments in thisproject are directed to the use of MALDI to obtain themeasurement of the absolute molecular mass distributionof synthetic polymers.

More definitive results were obtained on a new type ofmatrix for MALDI, tri-α-naphyl benzene, that forms bothglass and crystalline states. By SANS it was shown thatPSD is molecularly dispersed in the glass, but segregated inthe crystalline state. Figure 1 below shows that the MALDIsignal is inferior when PSD is dispersed molecularly in theglass compared to the MALDI signal obtained when PSD isphase separated.

C.M. Guttman, B.J Bauer, W.R. Blair, W.E. Wallace, R. Goldschmidt, S.J. Wetzel,A.P. Weaver (Polymers Division, NIST)

Baselines in Data Analysis

To derive quantitative results from MALDI spectra caremust be given to treatment of the baseline, particularly inspectra where the signal does not return to the same mini-mum value between each oligomeric peak. A common fea-ture in the MALDI spectrum of synthetic polymers is theappearance of a broad featureless hump that underlies thespectral data. The broad hump is usually offset to thehigher mass side with respect to the envelope of the peakdistribution and it may extend beyond the highest massidentifiable oligomeric peak. Including the hump as partof the polymer signal in the analysis can affect significantlyderived moments of the distribution (for comparisons withother methods, for example). In a set of definitive experi-ments it was shown that the broad hump results from frag-mentation products and polymer-matrix adducts. For thisreason the proper treatment is to eliminate the broad humpfrom spectral data to obtain the MMD and its moments.


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Approximately $140 billion are spent annually on healthcare measurements associated with biomedical devices,quality control and many other diagnostic and therapeuticprocedures. NIST workshops have identified needs forreference biomaterials (RBMs, 1998) and reference bioma-terial properties data (RBMPD, 2000). Among these werereference bars of medical grade Ultrahigh Molecular Mass(weight) Polyethylene (UHMWPE). NIST has respondedby stocking a supply of UHMWPE RM 8456 which be-came available in October 2000. At the 2000 RBMPD work-shop, participants identified a major need for a nationalbiomaterials properties database system. Properties of thedatabase system include portals with data from differentsources, one with data as supplied by manufacturers ofbiomaterials and biomedical devices, another with datafrom testing laboratories such as those of the FDA, and aNIST database with data from the literature and from cer-tificates that accompany NIST Reference Materials (RMs)and Standard Reference Materials of biomaterials. A prop-erty of the NIST database is that it contains critical evalua-tions of the properties included. Certificate data for refer-ence biomaterials was seen as an important source forcritically reviewed properties database. An alliance wasformed with several intraocular lens and biomaterial com-panies, and two major university eye clinical centers forthe development of intraocular lens reference materialsand reference data. Alliances are being pursued for atissue engineered products reference scaffold and for thedevelopment of additional orthopedic reference materials.

Support for theBiomaterials IntegratedProducts Industries

John Tesk

NIST workshops have established the needs of the medicaldevices industry (BIPIs) for reference materials, test meth-ods, and reference data. In this project a continual assess-ment is made of the technical needs of BIPIs to inform NISTmanagement for program planning. Leadership is taken tohelp form alliances, within and outside of NIST, to respondto those needs. Needs are explored through participationon numerous standards boards and their committees, oncommittees/boards of professional societies and academicinstitutions, and via liaisons with NIH, FDA, the AmericanAcademy of Orthopaedic Surgeons, and the AmericanDental Association.

Participation and leadership in standards organizations areseen as other means for assessing the needs for otherRMs and RBMPD. Collaboration continues with industryand an ASTM committee for the development and supplyof UHMWPE reference cubes that can be used for swell-ing measurements for the determination of crosslink den-sity as a result of ionizing radiation (crosslinking affectswear resistance and durability of orthopedic joint implantbearing surfaces).

A workshop on Standards for Biomedical Materials andDevices was identified by NIST major operating units at ameeting convened by the Materials Science and Engineer-ing Laboratory, as a means for establishment of a NIST-wide strategy for work on standards in support of thebiomedical devices industry. The Polymers Division held amajor role in the organization and operation of the work-shop, which was held on June 13, 2001. The workshopidentified action items for NIST early follow-up in supportof the biomedical materials and devices industry, and itemsfor consideration of future NIST responses to theindustry’s needs for standards.

Publications were also pursued to provide greater visibil-ity of NIST to the BIPIs community. An invited paper onthe proceedings of the RBMPD workshop was publishedin the July issue of the Journal of Biomedical MaterialsResearch, Applied Biomaterials.

J.A. Tesk, B.M. Fanconi (Polymers Division, NIST)

C. Croarkin (Statistical Engineering Division, NIST)

J. Sheets (Alcon Research), K. White (Polymer Technology Group), F. Eichmiller(American Dental Association Paffenbarger Research Center, NIST), J. Jacob (LSUEye Center), S. Spiegelberg (Cambridge Polymer Technology), S. Kurtz (ExponentInc.), B. Liebler, J. Benson (AdvaMed)


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The understanding and controlof extrusion instabilities is ham-pered by the lack of experimentaltechniques that provide real-time data at sufficient spatialand time scales. We recentlyhave upgraded the ExtrusionVisualization Facility so that itcan operate at high-speed/highmagnification. Using our newcapabilities, we collected anabundance of data that clarifiesseveral of the uncertaintiesregarding the nature of the sharkskin instability (see accom-plishment report). Buoyed by that success, we are openingefforts to study the “gross melt fracture instability”, todevelop new metrology to quantitate the polymer process-ing additive coating process, and to probe the correlationbetween instabilities and molecular architecture.

Sharkskin and Gross Melt Fracture

Using the extrusion visualization facility, we examine theflow behavior of the polymer as it is extruded through acapillary rod. High-speed microscopy of the material as itexits the tube reveals that the molten material tears at itssurface just at the exit from the tube. The central core of thematerial extrudes at high speed while the surface regiontears, peels off and then joins the central core (see Figure).

Current work is examining an extrusion instability known asgross melt fracture. This is characterized by severe distor-tions in the extruded material. Traditionally, it is believedthat this instability occurs in the region where the materialnarrows down from a large diameter to a small one, wellupstream of the capillary exit. However, we recently havediscovered that the exit region may be of importance. Wehave discovered that the material undergoes transient-spontaneous cavitation in the exit region of the tube duringgross melt fracture. We intend to understand cavitation andits implications for gross melt fracture control.

Control of ExtrusionInstabilities

Kalman B. Migler

Polymeric materials have become ubiquitous in the mod-ern economy because they are comparatively easy toprocess. However, polymeric materials exhibit complexand sometimes catastrophic responses to the forces im-posed on them during manufacturing. These instabilitieslimit the rates at which the materials can be processed. Inthis project we seek new measurement technologies tounderstand and control processing instabilities.

Measurement of In-situ CoatingProcess

Polymer Processing Aids (oftenfluorocopolymers) eliminate sharkskinby reducing the extensional deforma-tion of the polymer as it exits the die.In order to work, the fluoro-copoly-mer must first coat the die’s internalsurface. This coating process is criti-cal to product performance, yet thereare no in-situ quantitative measuresof the coating. Here, we seek a newmeasurement technique for the coat-

ing of a fluoropolymer additive based on evanescent waveinduced shifts in optical reflection. We propose to measurequantitatively the formation and growth of the fluoro-poly-mer layer onto the solid wall through use of total internalreflection. When the fluoropolymer starts to coat the inter-nal wall, the conditions of total internal reflection will be metand dramatic changes in optical reflection are predicted. Thethickness of the fluoropolymer layer at which this techniquefirst becomes effective is determined by the penetrationdepth of the evanescent wave (the exponentially decayinglight that does not become reflected). For the materials usedhere, the effects of the wall will be felt when its thickness isapproximately 100 nm, which is exceptional for an opticalmeasurement.

Molecular Architecture and Extrusion Instabilities

One of the great challenges in rheology is to elucidate theconnection between molecular architecture and rheology,and to apply this knowledge to the study of flow instabili-ties. This question is particularly important because recentsynthetic strategies allow for precise control of the molecu-lar architecture, such as long chain branching and molecularmass distribution. We are starting a project to use and de-velop our measurement tools to examine critical flow param-eters at the onset of various extrusion instabilities. We willcorrelate these measurements with characterized materialsthat have systematic variations in architecture.

K.B. Migler, P.M. McGuiggan, Y. Son (Polymers Division, NIST)

3M Canada Co., 3M Company, Dyneon LLC, Dow, MMI


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Optical Technique

Over the past several years we have concentrated ourattention on the development and use of optical techniquesinvolving light transmission and fluorescent molecularprobes. We have instrumented extrusion and injectionmolding machines and shown how optical sensors canprovide a wealth of information about the resin under pro-cessing conditions. When selected fluorescent probe mol-ecules are added to the resin, we can use them to monitorresin temperature and molecular orientation. The fluores-cent probes are mixed with the resin at very low concentra-tions, less than 10-5 mass fraction of dye in the resin.

A class of fluorescence moleculescalled band definition dyes is usedto measure temperature. We havediscovered several dyes that sur-vive processing temperatures upto 300 oC. They are benzoxazolylstilbene (BOS), perylene, andbis(di-tert-butylphenyl)-perylenedicarboximide (BTBP). These dyesdisplay their fluorescence in dis-tinct spectral bands that haveindividual temperature depen-dence. The basis for measuringtemperature is the temperaturedependence of the shape of the fluo-rescence spectrum.

The fluorescence temperature mea-surement method is used in collabora-tive programs with three industrialR&D laboratories—Exxon/MobilFilms, DOW Chemical, and Data-pointLabs. At Exxon/Mobil we are monitor-ing the temperature of biaxiallystretched polypropylene films thatcontain the fluorescent dye BTBP.

Real-Time ProcessMonitoring

Real-time, on-line measurements of resin materials prop-erties are desirable not only because they preempt theneed for post processing characterization but also be-cause they can be used to monitor resin conditions, todetect problems with processing parameters and to con-trol the process. In this project, we are developing mea-surement techniques based on optical, dielectrics, andultrasonics techniques. The work involves the design andconstruction of sensors and the application of thesesensors to real-time process monitoring.

The temperature measurement is obtained from the BTBPfluorescence spectrum by measuring the ratio of intensitiesat 544 nm and 577 nm. The biaxial stretching must be carriedout between 155 oC and 162 oC. Typical steady-state moni-toring is shown in the upper figure. The standard uncer-tainty for the temperature measurements is 2 oC.

Dielectric Measurements

In collaboration with Chemical ElectroPhysics Corp. (CEP),we have carried out in-line dielectric measurements duringextrusion of filled polymers. CEP’s in-line dielectric cell hasa ring design with the inner surface of the ring containinginterdigitated electrodes. The cell is contained in a tempera-

ture control housing and isattached to the exit of an ex-truder. By applying a smallvoltage to the electrodes, afringing field intercepts theresin flowing through the ring.Associated circuitry in con-junction with calibration of theinstrument yields measure-ments of permittivity and con-ductivity. Real-time measure-ments of filled polymers areused to monitor filler concen-tration, transition times be-tween resin loadings, and thedielectric properties of the melt.

Consider the data shown at leftfor processing of polystyrenefilled with aluminum oxide. Thedata are a plot of relative per-mittivity versus time for pro-cessing of polystyrene filledwith 20 percent by mass alumi-num oxide powder. The uncer-tainty in permittivity measure-ments is 0.01.

Anthony J. Bur

A.J. Bur, S.C. Roth (Polymers Division, NIST)

Exxon/Mobil Films, Dow, Data-point Labs, Chemical ElectroPhysics Corporation


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Micro-scale Processing

Kalman B. Migler

Micro-scale processing is an emerging technology withapplications in the optical, medical, and “lab-on-chip”industries. However, many concepts developed for macro-scopic processing break down in this regime. The goal ofthis work is to advance the technology infrastructure tosupport the growth of these industries.

K.B. Migler, J. Pathak, Y. Son (Polymers Division, NIST)

N. Martys (Building and Fire Research Laboratory, NIST)

J.E. Devaney (Information Technology Laboratory, NIST)

We are exploring theeffects of confinementand the breakdown ofmixing that occur inthe micro-scale regime.The two sub-projectsdescribed below aredesigned to bring thesynergistic advan-tages brought bypolymer blending intothe fabrication ofsmall-scale structures.

Confinement andStability of LiquidThreads

It has been knownsince the 19th centurythat a liquid thread immersed in a fluid is unstable—itbreaks into a sequence of droplets. Recently we haveshown that it is possible to stabilize the thread by confin-ing it between two parallel walls. This result is important inemerging micro-fluids technology as well as in micro-injection molding. By combining experiments, interfacialarea calculations, and Lattice-Boltzman numerical simula-tions (See Figure), we systematically explore the relevantparameter space. The emerging confluence between theexperimental and numerical results will allow us to modeland optimize the behavior in complex geometries beforebuilding actual devices.

Further application of this work has led to the develop-ment of an improved method for the measurement of inter-facial tension that combines the advantages of existingtechniques while eliminating their disadvantages. We thusbelieve that it will become the method of choice for interfa-cial tension measurements in polymer blends.

String Structuresin Confined Blends

Last year, we re-ported the unex-pected discovery ofstring formation insheared polymerblends that occurswhen the dropletsize becomes com-parable to the gapwidth. Now, we areexploring the conse-quences of thisfinding and therange of conditionsover which it isvalid. We find thatstring formation is

extremely robust, occurring over a wide range of micro-scaleprocessing conditions. We have observed it over a widerange of compositions, with string formation occurring atvolume fractions as low as 5 percent, over a range of vis-cosity ratios from (0.1 to 10) and over a range of elasticities.We find that extreme care must be taken to ensure the stringmorphology is appropriate to the application. Our work alsopoints the way to potential uses of the technology, forexample to produce scaffolds in tissue-engineered products.

We also report the discovery of layering transitions thatoccur when the shear rate is too high to produce the stringstructure. We observe that the droplets organize into one,two, or three layer systems as they are sheared. Theseresults further emphasize the profound changes that areinduced by confinement.

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Publications

Akpalu, Y. A. and Amis, E. J., “The Effect of Polydispersityon the Evolution of Density Fluctuations to LamellarCrystals in Linear Polyethylene”; Journal of ChemicalPhysics, 2000 Jul 1; 113(1):392–403.

Amis, E. J. and Fanconi, B. M., “Polymer Division FY2000Programs and Accomplishments”; NISTIR 6596, 2000.

Antonucci, J. M.; McDonough, W. G.; Schumacher, G. E.,and Shimada, Y., “A Novel Microshear Bond Test ToMeasure Dental Adhesion”; Proc. of the 24th AnnualMeeting of the Adhesion Society; Williamsburg, VA,2001.

Antonucci, J. M.; Skrtic, D., and Brunworth, R. T.,“Methacrylate Conversion in Photo-polymerizedComposites Containing Amorphous CalciumPhosphate Fillers”; Polymer Materials Science &Engineering; in press.

Baklanov, M. R.; Kondoh, E.; Lin, E. K.; Gidley, D. W.; Lee,H.-J.; Mogilnikov, K. P., and Sun, J. N., “ComparativeStudy of Porous SOG Films with Different Non-Destructive Instrumentation”; Proc. of the Intl.Interconnect Technology Conf.; 2001.

Barnes, K. A.; Douglas, J. F.; Liu, D.-W., and Karim, A.,“Influence of Nanoparticles and Polymer Branchingon Rewetting of Polymer Films”; Journal of Colloidand Interface Science; in press.

Bauer, B. J. and Amis, E. J., “Characterization ofDendritically Branched Polymers by SANS, SAXS,and TEM”, in Dendritic Polymers, ed.: Tomalia, D. A.and Frechet, J. M. J.; in press.

Bauer, B. J.; Guttman, C. M.; Blair, W. R., and Liu, D.-W.,“Tri-alpha-Napthyl Benzene as a Glassy or CrystallineMatrix for MALDI TOF MS of Synthetic Polymers”;Proc. of the 49th American Society for MassSpectrometry Conf.; Chicago, IL, 2001.

Bauer, B. J.; Lin, E. K.; Lee, H. J.; Wang, H., and Wu, W.-L.,“Structure and Property Characterization of Low-kDielectric Porous Thin Films”; Journal of ElectronicMaterials, 2001 Apr; 30(4): 304–308.

—, “Structure and Property Characterization of Low-kDielectric Porous Thin Films; Polymer Preprints, 2001;42(1):263–264.

Bauer, B. J.; Wallace, W. E.; Fanconi, B. M., and Guttman,C. M., “‘Covalent Cationization Method’ for theAnalysis of Polyethylene by Mass Spectrometry”;Polymer; in press.

Beers, K. L.; Douglas, J. F.; Amis, E. J., and Karim, A., “AHigh Throughput Approach to Crystallization in ThinFilms: Isotactic Polystyrene”; Polymer Preprints, 2001;42(2).

Bouldin, C. E.; Wallace, W. E.; Lynn, G. W.; Roth, S. C.,and Wu, W.-L.,“Thermal Expansion Coefficients ofLow-k Dielectric Films from Fourier Analysis ofX-Ray Reflectivity”; Journal of Applied Physics, 2000Jul 15; 88(2):691–695.

Bubeck, R. A.; Bauer, B. J.; Dvornic, P.; Owen, M. J.;Reeves, S.; Parkham, P., and Hoffman, L. W., “Small-Angle Neutron Scattering from Metal Ion-ContainingPAMAMOS Dendrimer Networks”; ACS PMSEPreprints; in press.

Bur, A. J.; Migler, K. B., and Roth, S. C., “ProcessMonitoring at the National Institute of Standards andTechnology: Celebrating 100 Years of MeasurementExcellence”; Proc. of the Society of Plastics Engineers2001 Annual Technical Conference, 2001.

Bur, A. J.; Roth, S. C., and Lobo, H., “TemperatureMonitoring of Capillary Rheometry Using aFluorescence Technique”; Proc. of the Society ofPlastics Engineers Annual Technical Meeting, 2001.

Bur, A. J. and Roth, S. S., “Fluorescence BasedTemperature Measurements and Applications to Real-Time Polymer Processing”; NISTIR, 2000.

Cantoni, G.; Bonner, R. F.; Malekafzali, A.; Douglas, J. F.;Amis, E. J.; Karim, A., and Sehgal, A., “Laser DiodeFocal Activation of Polymer for New Uses inGenomics and Gene Expression Research byCombination of Laser Capture Microdissection withMedical Molecular Diagnostics”; Conf. Proc. of theXIV Congresso della Divisione di Chimica Industrialedella Societa Chimica Italiana; Milan, Italy, 2001.

Chai, H.; Chiang, M. Y. and Schultheisz, C. R., “Effect ofStraining Rate on the Mechanical Behavior ofAdhesive Bonds Under Shear Deformation”; Proc. ofthe Adhesion Society Meeting, pp. 303–305;Williamsburg, VA, Feb 2001.

Publications

55

Chen, R.; Yalcin, T.; Wallace, W. E.; Guttman, C. M., and Li,L.,“Laser Desorption Ionization and MALDI Time-of-Flight Mass Spectrometry for Low Molecular MassPolyethylene Analysis”; Journal of the AmericanSociety for Mass Spectrometry; in press.

—, “Laser Desorption Ionization and MALDI Time-of-Flight Mass Spectrometry for Low Molecular MassPolyethylene Analysis”; Proc. of the 49th ASMSConference on Mass Spectrometry and Allied Topics;Chicago, IL; in press.

Chiang, C. K.; Popielarz, R., and Sung, L. P., “DielectricProperties and Morphology of Ferroelectric Ceramic-Polymer Composite Films”; Symp. Proc. of MaterialsResearch Society—Microelectronics andMicrosystems Packaging, 2001.

Chiang, C. K.; Sung, L. P., and Popielarz, R., “Investigationof Morphology and Interface in Polymer CompositeThin Films”; Symp. Proc. of Materials ResearchSociety, 2001.

Crosby, A. J.; Karim, A., and Amis, E. J., “CombinatorialInvestigations of Polymer Adhesion”; PolymerPreprints; in press.

DeReggi, A. S.; Balizer, E.; Neumann, D. A., and Bateman,F., “Electrostriction Mechanism in Electron-IrradiatedFerroelectric Copolymer: A Frequency ResponseModel”; Conference on Electrical Insulation andDielectric Phenomena, 2000.

Douglas, J. F.; Kent, M. S.; Satija, S. K., and Karim, A.,“Swelling of Grafted Polymer ‘Brushes’”;Encyclopedia of Materials: Science and Technology;in press.

Douglas, J. F.; Zhang, Y.; Ermi, B,. D., and Amis, E. J.,“Influence of Counterion Valency on the ScatteringProperties of Highly Charged PolyelectrolyteSolutions”, Journal of Chemical Physics, 2001 Feb;3299–3313.

Dunkers, J. P.; Holmes, G. A., and McDonough, W. G.,“Imaging of Multi-fiber, Micro-mechanical TestingSpecimens Using Optical Coherence Tomography”;Proc. of the 24th Annual Meeting of the AdhesionSociety; Williamsburg, VA, 2001.

Dunkers, J. P.; Lenhart, J. L.; Kueh, S. R.; van Zanten,J. H.; Advani, S. G., and Parnas, R. S.,“Fiber OpticsFlow and Cure Sensing for Liquid CompositeMolding”; Journal of Optics and Lasers inEngineering, 2001; 35:91–104.

Dunkers, J. P.; Phelan, F. R.; Flynn, K. M.; Sanders, D. P.,and Parnas, R. S., “Permeability Prediction from Non-Destructive Imaging of Composite Microstructure”;Society of Plastics Engineers 2001 Annual TechnicalConference Proceedings, 2001.

Dunkers, J. P.; Phelan, F. R.; Sanders, D. S.; Everett, M. J.;Green, W. H.; Hunston, D. L., and Parnas, R. S., “TheApplication of Optical Coherence Tomography inProblems in Polymer Matrix Composites”; Journal ofOptics and Lasers in Engineering, 2001; 35:135–147.

Dunkers, J. P.; Washburn, N. R.; Simon, C. G.; Karim, A.,and Amis, E. J., “Non-destructive Characterization ofthe Morphology of a Polymer Co-Extruded ScaffoldUsing Optical Coherence Tomography”; Proc. of the2001 Annual Meeting of the Society of Biomaterials,2001.

Eichmiller, F. C.; Tesk, J. A., and Croarkin, C. M.,“Mechanical Properties of Ultra High MolecularWeight Polyethylene NIST Reference Material#8456”; Proc. of the 2001 Annual Meeting of theSociety of Biomaterials, 2001.

Feresenbet, E. B.; Holmes, G. A., and Raghavan, D., “TheInfluence of Silane Coupling Agent Composition onthe Fiber-Matrix Interfacial Shear Strength”; Proc. ofthe 24th Annual Meeting of the Adhesion Society;Williamsburg, VA, 2001.

Ferreiro, V.; Douglas, J. F.; Karim, A., and Amis, E. J.,“Phase Ordering in Blend Films of Semi-Crystallineand Amorphous Polymers”; MacromolecularSymposium, 2001; 167:73–88.

Ferreiro, V.; Schmidt, G.; Han, C. C., and Karim, A.,“Dispersion and Nucleating Effects of Clay Fillers inNanocomposite Polymer Films”; Polymer Preprints,2001.

Flynn, K. M.; Fanconi, B. M. and Amis, E. J., CD-ROMPolymer 2000 Publications; NISTIR, 2000.

Fuoco, E.; Gillen, G.; Wijesundara, M. B. J.; Wallace, W. E.,and Hanley, L., “Surface Analysis Studies of YieldEnhancements in Secondary Ion Mass Spectrometryby Polyatomic Projectiles”; Journal of PhysicalChemistry B, 2001; 105:3950.

Gebremichael, Y.; Schroder, T. B.; Starr, F. W., and Glotzer,S. C., “Spatially Correlated Dynamics in a SimulatedGlass-Forming Polymer Melt: Analysis of ClusteringPhenomena”; Physical Review E; in press.

Glotzer, S. C. and Starr, F. W., “Multiscale Modeling ofFilled and Nanofilled Polymers”; Proc. of Foundationsof Molecular Modeling and Simulation, 2000.

Publications

56

Goldfarb, D. L.; Lin, Q.; Angelopoulos, M.; Soles, C. L.;Lin, E. K., and Wu, W.-L., “Characterization of Thinand Ultrathin Polymer and Resist Films”, SPIEProceedings; 2001.

Goldschmidt, R. J. and Guttman, C. M., “Investigation ofTwo Broad Features Often Observed in MALDI MassSpectra of Synthetic Polymers”; Proc. of the 49th

American Society for Mass Spectrometry Conf.;Chicago, IL, 2001.

Grull, H.; Schreyer, A.; Berk, N. F.; Majkrzak, C. F., andHan, C. C., “Composition Profiling in a Binary PolymerBlend Thin Film Using Polarized NeutronReflectivity”; Europhysics Letters, 2000 Apr;50(1):107–112.

Guttman, C. M., “Mass Spectrometry”, in Encyclopedia ofPolymer Science and Technology; in press.

Guttman, C. M.; Blair, W. R., and Wetzel, S. J., “MakingMALDI-TOF-MS an Absolute Method forDetermination of the MMD of Polymers”; PolymerPreprint, 2001; 42(1), 277–78.

Guttman, C. M.; Wetzel, S. J.; Blair, W. R.; Fanconi, B. M.;Girard, J. E.; Goldschmidt, R. J.; Wallace, W. E., andVanderHart, D. L., “National Institute of Standardsand Technology Sponsored InterlaboratoryComparison of Polystyrene Molecular MassDistribution Obtained by Matrix Assisted LaserDesorption Ionization Time-of-Flight MassSpectrometry: Statistical Analysis”; AnalyticalChemistry, 2001; 73:1252–1262.

Han, C. C.; Hobbie, E. K.; Nakatani, A. I., and Kim, S.,“Critical Temperature Shift and Mixing in PolymerBlends under Simple Shear Flow”; Journal of thePhysical Society of Japan, Supplement A , 2001;70:317.

Han, C. C.; Schmidt, G.; Nakatani, A. I., and Butler, P., “ASmall Angle Neutron Scattering Study on PolymerClay Solutions”; Polymer Preprints, 2001.

Han, C. C.; Schmidt, G.; Nakatani, A. I., and Karim, A.,“Characterization of Polymer-Clay Solutions byRheology, Flow Birefringence and SANS”; PolymerPreprint, 2001.

Hayashi, M.; Grull, H.; Esker, A. R.; Weber, M.; Sung, L.;Satija, S. K.; Han, C. C., and Hashimoto, T., “NeutronReflectivity Study of Diblock Formation DuringReactive Blending Processes”; Macromolecules, 2000Aug 22; 33(17):6485–6494.

Hayashi, M.; Hashimoto, T.; Hasegawa, H.; Takenaka, M.;Grull, H.; Esker, A. R.; Weber, M.; Satija, S. K.; Han,C. C., and Nagao, M., “Interface Between aPolysulfone and Polyamide as Studied by CombinedNeutron Reflectivity and Small-Angle NeutronScattering Techniques”; Macromolecules, 2000 Oct31; 33(22):8375–8387.

He, J.; Chiang, M. Y., and Hunston, D. L., “Assessment ofSandwich Beam in Three-Point Bending forMeasuring Adhesive Shear Modulus”; Transactionof the ASME, Journal of Engineering Material andTechnology, 2000.

Holmes, G. A.; Feresenbet, E. B., and Raghavan, D., “TheEffect of Self-Assembled Monolayer Technology onFiber-Matrix Adhesion”; Polymer Preprints, 2001;42(1):296–297.

—, “Using Self-Assembled Monolayer Technology toProbe the Fiber-Matrix Interface”; Proc. of the 24th

Annual Meeting of the Adhesion Society;Williamsburg, VA, 2001.

Holmes, G. A. and Ford, K., “Epoxy Clay Hybrid (ECH)Nanocomposites: Strategies for the Dispersion ofClay Platelets in Amine-Cured Epoxy Resins”; Proc. ofthe 16th Annual Technology Conference onComposite Materials, 2001.

Holmes, G. A. and Peterson, R. C., “Measuring InterfaceStrength in Single Fiber Composites: The Effect ofStress Concentrations”; Proc. of the MaterialsResearch Society Annual Mtg., 2000.

Holmes, G. A.; Peterson, R. C.; Hunston, D. L., andMcDonough, W. G., “E-Glass/DGEBA/m-PDA SingleFiber Composites: Interface Debonding During FiberFracture”; Polymer Composites; in press.

Hu, X. S.; Shin, K.; Rafailovich, M.; Sokolov, J.; Stein, R.;Chan, Y.; Williams, K.; Wu, W.-L., and Kolb, R.,“Anomalies in the Optical Index of Refraction of SpunCast Polystyrene Thin Films”; High PerformancePolymers, 2000 Dec; 12(4):621–629.

Hunston, D. L., “Load History Dependence of Fracture inStructural Adhesives”; Adhesives Age; in press.

Hunston, D. L.; Juska, T.; Karbhari, V.; Morgon, R., andWilliams, C., “Gap Analysis for Durability of FiberReinforced Polymer (FRP) Composites in CivilInfrastructure”; Report from Civil EngineeringResearch Foundation, 2001.

Hunston. D. L.; Miyagi, Z.; Schultheisz C. L., and Beirson,H., “Sandwich Bending Specimens for CharacterizingAdhesive Properties”; Mechanisms of Time-Dependent Materials; in press.

Publications

57

Jeon, H. S. and Hobbie, E. K., “Erratum: Shear Viscosity ofPhase-Separating Polymer Blends with ViscousAsymmetry [PRE 63, 061403 (2001)]”; PhysicalReview E.

—,“Shear Viscosity of Phase Separating Polymer Blendswith Viscous Asymmetry”; Physical Review E., 2001;63:1403–1408.

Jeon, H. S.; Nakatani, A. I.; Han, C. C., and Colby, R. H.,“Melt Rheology of Lower Critical SolutionTemperature Polybutadiene/Polyisoprene Blends”;Macromolecules, 2000 Dec 26; 33(26):9732–9739.

Jeon, H. S.; Nakatani, A. I.; Hobbie, E. K., and Han, C. C.,“Phase Inversion of Polybutadiene/PolyisopreneBlends Under Quiescent and Shear Conditions”;Langmuir, 2001; 17:3087–3095.

Jiang, Y.; Saxena, A.; Lookman, T., and Douglas, J. F.,“Influence of Filler Particles and Clusters on PhaseSeparation in Binary Polymer Blends”; Journal of theMaterials Research Society; in press.

Josell, D. A.; Wallace, W. E., and Wheeler, D., “WaferLevel Underfill: Experiments and Modeling, SiliconMicroelectronics Programs at the National Institute ofStandards and Technology”; NISTIR 6731, 2001.

Josell, D. A.; Wallace, W. E.; Warren, J.; Wheeler, D., andPowell, A. C., “Alignment of Flip-Chip SolderedElectronic Components: Measured and CalculatedNormal and Laterial Force-DisplacementRelationships”; Journal of Electronics Packaging; inpress.

Karim, A. and Amis, E. J., “Combinatorial Methods atNIST”; NISTIR, 2001.

Karim, A.; Douglas, J. F.; Barnes, K. A.; Nakatani, A. I.;Liu, D. W., and Amis, E. J., “Studies of Polymer-fillerInteractions in Filled Systems”; ACS PMSE, 2001.

Karim, A.; Douglas, J. F.; Sung, L. P., and Ermi, B. D.,“Phase Separation in Ultra Thin Polymer BlendFilms”; in Encyclopedia of Polymer Science andTechnology; in press.

Karim, A.; Smith, A. P.; Douglas, J. F., and Amis, E. J.,“Characterization of Symmetric Diblock Copolymerswith High-Throughput Techniques”; PolymerPreprints, 2001; 42(1)283–284.

Kondoh, E.; Baklanov, M.R.; Lin, E.K.; Gidley, D.W. andNakashima, A., “Comparative Study of Pore Size ofLow-Dielectric Constant Porous Spin-on-Glass Filmwith Different Ways of Non-destructiveInstrumentation”; Japanese Journal of AppliedPhysics, 200l; 40: L323–L326.

Kumar, S. K. and Douglas, J. F., “Gelation in PhysicallyAssociating Polymer Solutions”, Physics ReviewLetters; in press.

Lee, H. J.; Lin, E. K.; Wang, H.; Wu, W.-L.; Chen, W., andDeis, T. A., “Correlations Between StructuralCharacteristics and Process Conditions of HSQ BasedPorous Low-k Thin Films”; Proc. of the MaterialsResearch Society Meeting, 2001.

Lee, H. J.; Lin, E. K.; Wang, H.; Wu, W.-L.; Chen, W., andDeis, T. A., “Characterization of Porous Low-kDielectric Thin Films Using X-ray Reflectivity andSmall-angle Neutron Scattering”; Proc. of the Intl.Interconnect Technology Conf., 2001.

Lee, H. J.; Lin, E. K.; Wu, W.-L.; Fanconi, B. M.; Lan, J. K.;Cheng, Y. L.; Liou, H. C.; Wang, Y. L.; Feng, M. S., andChao, C. G., “Investigation of N

2 Plasma Effects on the

Density Profile of Hydrogen Silsesquioxane ThinFilms”; Proc. of the Materials Research SocietyMeeting, 2001.

Lenhart, J. L.; van Zanten, J. H.; Dunkers, J. P., and Parnas,R. S., “Studying the Buried Interfacial Region with anImmobilized Fluorescence Probe”; Macromolecules,2001; 34:2225–2231.

—,“Using a Localized Fluorescent Dye To Probe the Glass/Resin Interphase”; Polymer Composites; in press.

Lenhart, J. L.; van Zanten, J. H.; Dunkers, J. P.; Parnas,R. S., and Woerdeman, D. L., “Localizing a FluorescentDye To Probe the Buried Interfacial Chemistry”; Proc.of the 24th Annual Meeting of the Adhesion Society;Williamsburg, VA, 2001.

Lin, E. K.; Lee, H. J.; Bauer, B. J.; Wang, H.; Wetzel, J. T.,and Wu, W.-L., “Structure and PropertyCharacterization of Low-k Dielectric Porous Thin FilmsDetermined by X-ray Reflectivity and Small-AngleNeutron Scattering, in Low Dielectric ConstantMaterials for IC Applications, ed.: P.S. Ho, J. Leu andW. W. Lee: Springer Publishing Inc; in press.

Lin, E. K.; Soles, C. L.; Wu, W.-L.; Satija, S. K.; Lin, Q., andAngelopoulos, M., “Neutron ReflectivityMeasurements for the Interfacial Characterization ofPolymer Thin Film Photoresists”; Proc. of the 12th Intl.Conf. on Photopolymers, 2001.

Lin, E. K.; Wu, W.-L.; Lin, Q. H., and Angelopoulos, M.,“Feature-shape and Line-edge RoughnessMeasurement of Deep Sub-micron LithographicStructures Using Small-Angle Neutron Scattering”;Proc. of the SPIE 26th Annual Intl. Conf. onMicrolithography, 2001.

Publications

58

Lomov, S. V.; Huysmans, G.; Luo, Y.; Parnas, R. S.;Prodromou, A.; Verpoest, I., and Phelan, Jr., F. R.,“Textile Composites. Modeling Strategies.Composites A: Applied Science and Manufacturing,2001; 32(10):1379–1394.

Lynn, G. W.; Dadmun, M. D.; Wu, W.-L.; Lin, E. K., andWallace, W. E., “Neutron Reflectivity Studies of theInterface Between a Small Molecule Liquid Crystaland a Polymer”; Liquid Crystals; in press.

Majumdar, B. S. and Hunston, D. L., “Continuous ParallelFiber Composites: Fracture”; in Encyclopedia ofMaterials: Science and Technology; Oxford, England:Pergamon Press; in press.

Mansfield, M. L.; Douglas, J. F., and Garboczi, E. J.,“Intrinsic Viscosity and the Electric Polarizability ofArbitrarily Shaped Objects”; Physical Review E.; inpress.

Martys, N. S. and Douglas J. F., “Critical Properties andPhase Separation in Lattice Boltzmann Fluid Mixtures;Physical Review E. 2001; 63(031205):1–15.

McBrearty, M.; Bur, A. J., and Roth, S. C., “In-lineDielectric Monitoring During Extrusion of FilledPolymers”; Proc. of the Society of Plastics Engineers2001 Annual Technical Meeting Conference, 2001.

McDonough, W. G.; Amis, E. J., and Kohn, J., “CriticalIssues in the Characterization of Polymers for MedicalApplications”; NISTIR 6535, 2000.

McDonough, W. G.; Antonucci, J. M., and Dunkers, J. P.,“Interfacial Shear Strengths of Dental Composites bythe Microbond Test”; Dental Composites; Vol 17/6492–498.

McDonough, W. G.; Antonucci, J. M.; Schumacher, G. E.,and Shimada, Y., “A Microshear Test To Measure theBond Between Dental Composites and DentalSubstrates”; NISTIR 6535, 2000.

McGuiggan, P. M., “The Boundary Lubrication Propertiesof Model Esters”; Tribology Letters; in press.

Meredith, J. C.; Smith, A. P.; Karim, A., and Amis, E. J.,“Combinatorial Materials Science for Polymer Thin-Film Dewetting”; Macromolecules, 2000 Dec 26;33(26):9747–9756.

Meredith, J. C.; Tona, A.; Elgendy, H.; Karim, A., andAmis, E.J., “Combinatorial Characterization ofBiodegradable Polymers; Polymer Preprints, 2001;42(1):273–274.

Migler, K. B., “Extrusion Visualization from Blend Structureto Sharkskin”; Proc. of the Society of PlasticsEngineers 2001 Annual Technical Conference, 2001.

—, “String formation in sheared polymer blends:Coalescence, breakup, and finite size effects”;Physical Review Letters, 2001; 86:1023–1026.

Migler, K. B.; Lavallée, C.; Dillon, M. P.; Woods, S. S., andGettinger, C. L., “Visualizing the elimination ofsharkskin through fluoropolymer additives: Coatingand polymer-polymer slippage”; Journal of Rheology,2001; 45:565–581.

—, “Flow Visualization of Polymer Processing AdditiveEffects”; Proc. of the Society of Plastics Engineers2001 Annual Technical Conference, 2001.

Morgan, A. B.; Jackson, C. L., and Gilman J. W.“Characterization of the Dispersion of Clay in aPolyetherimide Nanocomposite”; Macromolecules, inpress.

Nakatani, A. I.; Chen, W.; Schmidt, R. G., and Han, C. C.,“Chain Dimensions in Polysilicate-FilledPoly(Dimethyl Siloxane)”; Polymer, 2001; 42:3713–3722.

Nakatani, A. I.; Ivkov, R.; Papanek, P.; Jackson, C. L.;Yang, H.; Nikiel, L., and Gerspacher, M., “TheSignificance of Percolation on the Dynamics ofPolymer Chains Bound to Carbon Black”; MRSSymposium Proc., 2001.

Nakatani, A. I.; Ivkov, R.; Papanek, P.; Yang, H., andGerspacher, M., “Inelastic Neutron Scattering FromFilled Elastomers”; Rubber Chemistry andTechnology, 2000 Nov–2000 Dec 31; 73(5):847–863.

Nakatani, A. I.; Kwan, K. S.; Ivkov, R., and Papanek, P.,“Silica Surface Treatment Effects on the Dynamics ofPoly(Dimethyl Siloxane) by Time-of-Flight NeutronSpectroscopy”; Polymer Preprints, 2001; 42(1):176–177.

Netz, P. A.; Starr, F. W.; Stanley, H. E., and Barbosa, M. C.,“Static and Dynamic Properties of Stretched Water”;Journal of Chemical Physics, 2001; 115(1):344–348.

Niranjan, P. S.; Forbes, J. B.; Greer, S. C.; Dudowicz, J., andDouglas, J. F., “Thermodynamic Regulation of ActinPolymerization”; Journal of Chemical Physics, 2001;114:10573–10576.

Nyden, M. R.; VanderHart, D. L., and Alamo, R. G., “TheConformational Structures of Defect-ContainingChains in the Crystalline Regions of IsotacticPolypropylene”; Computational and TheoreticalPolymer Science, 2001; 11:175–189.

Publications

59

Obrzut, J., “Dielectric Characterization of EmbeddedDecoupling Capacitance Films at MicrowaveFrequencies”; Proc. of the SMTA 6th Annual New &Emerging Technologies for Electronic Packaging andAssembly; Dallas, TX, 2000.

Obrzut, J., “ Embedded Capacitance Materials”; EmbeddedDecoupling Capacitance Project Final Report, 2000Dec.

Obrzut, J. and Nozaki, R., “Broadband Characterization ofDielectric Films for Power-Ground Decoupling”; IEEEInstrumentation and Measurements Technology,Transactions Proceedings; Budapest, Hungary, 2001.

—, “Permittivity Measurements of Solid Film Dielectrics atMicrowave Frequencies”; IPC EXPO TechnicalConference; San Diego, CA, 2000.

Phelan, F. R., “Model Based Predictions of Permeability inPreform Materials”; Proc. Society of PlasticsEngineers 2001 Annual Technical Conference, 2001.

Phelan, F. R.; Hobbie, E.; Jeon, H.; Glotzer, S. G., and Han,C. C., “Modeling Drop Size Distribution in PolymerBlend Injection Molding”; Proc. Society of PlasticsEngineers 2001 Annual Technical Conference, 2001.

Pochan, D. J.; Lin, E. K.; Satija, S. K., and Wu, W.-L.,“Thermal Expansion of Supported Thin Polymer Films:a Direct Comparison of Free Surface Vs TotalConfinement”; Macromolecules, 2001 Apr 24;34(9):3041–3045.

Qiao, F.; Migler, K. B.; Hunston, D. L., and Han, C. C.,“Reactive Compatibilization and In-lineMorphological Analysis of Blends of PET and aThermotropic Liquid Crystalline Polymer”; PolymerEngineering and Science, 2001; 41:77–85.

Raghavan, D.; Gu, X.; Nguyen, T.; VanLandingham, M.,and Karim, A., “Mapping Polymer HeterogeneityUsing Atomic Force Microscopy Phase Imaging andNanoscale Indentation”; Macromolecules, 2000; 33:2573–2583.

Scala, A.; Starr, F. W.; La Nave, E.; Stanley, H. E., andSciortino, F., “Free Energy Surface of SupercooledWater”; Physical Review E., 2000 Dec; 62(6):8016–8020.

Schmidt, G.; Nakatani, A. I.; Butler, P.; Ferreiro, V.; Karim,A., and Han, C. C., “Polymer-Clay NanocompositeMaterials, Solution and Bulk Properties”; Proc. of theMaterials Research Society Symposium, 2001.

Schroder, T. B.; Sastry, S.; Dyre, J. C., and Glotzer, S. C.,“Crossover to Potential Energy Landscape DominatedDynamics in a Model Glass-Forming Liquid”; Journalof Chemical Physics, 2000 Jun 8; 112(22):9834–9840.

Schultheisz, C. R. and Leigh, S., “Certification of theRheological Behavior of SRM 2490, PolyisobutyleneDissolved in 2,6, 10, 14 tetramethyl pentadecave;NIST Special Publication 260–142, 2001.

Schultheisz, C. R. and McKenna, G. B., “StandardReference Materials: Non-Newtonian Fluids forRheological Measurements”; Proceedings of theSociety of Plastics Engineers 2001 Annual TechnicalConference; Volume 6, 1100–1104, Dallas, TX, May2001.

Skrtic, D.; Antonucci, J. M.; Eanes, E. D., and Brunworth,R. T., “Silica- and Zirconia-hybridized AmorphousCalcium Phosphate. Effect on Transformation toHydroxyapatite”; Journal of Biomedical MaterialsResearch; in press.

Smith, A. P.; Carson, J. C.; Douglas, J. F., and Karim, A.,“Combinatoric Study of Surface Pattern Formation inThin Block Copolymer Films”; Physical ReviewLetters, 2001; 87:015503-1-4.

Smith, A. P.; Meredith, J. C.; Douglas, J. F.; Amis, E. J., andKarim, A., “High-Throughput Characterization ofPattern Formation in Symmetric Diblock CopolymerFilms”; Journal of Polymer Science: Polymer Physics;in press.

Smith, A. P.; Sehgal, A.; Amis, E. J., and Karim, A.,“Characterization of Surface Energy Effects onMorphology of Thin Diblock Copolymer Films byHigh Throughput Techniques”; Polymer Preprints,2001.

Snyder, C. R., “High Sensitivity Technique forMeasurement of Thin Film Out-of-Plane Expansion.II. Conducting and Semiconducting Samples”;Characterization and Metrology for ULSI Technology:2000 International Conference, 2000.

Soles, C. L.; Dimeo, R. M.; Neumann, D. A.; Kisliuk, A.;Sokolov, A. P.; Liu, J. W., and Yee, A. F., “Correlationsof the Boson Peak With Positron Annihilation inSeries of Polycarbonate Copolymers”;Macromolecules, 2001 Jun 5; 34(12):4082–4088.

Soles, C. L.; Douglas, J. F., Dimeo, R. M., and Wu W.-L.,“The Dynamics of Confined Polycarbonate ChainsProbed with Incoherent Neutron Scattering”; PolymerMaterials Science and Engineering, 2001; 85.

Soles, C. L.; Lin, E. K.; Wu, W.-L.; Lin, Q., andAngelopoulos, M., “Confinement Induced Deviationin Ultra-thin Photoresist Films”; Proc. of the SPERETECH 12th Intl. Conf. on Photopolymers, 2001.

Publications

60

Starr, F. W. and Glotzer, S. C., “Simulation of Filled PolymerMelts on Multiple Length Scales”; Proc. of MaterialsResearch Society, 2001; 661.

Starr, F. W.; Sastry, S.; La Nave, E.; Stanley, H. E., andSciortino, F., “Free Energy Surface of SupercooledWater”; Physical Review E, 2001; 62:041201.

Starr, F. W; Schroeder, T. B., and Glotzer, S. C., “MolecularDynamics Simulation of a Polymer Melt with aNanoscopic Particle”; Macromolecules; in press.

Strawhecker, K. E.; Kumar, S. K.; Douglas, J. F., andKarim, A., “The Critical Pole of Solvent Evaporationon the Roughness of Spun Cast Polymer Films”;Macromolecules, 2001; 34:4669–4672.

Tecklenburg, R. E.; Chen, H., and Wallace, W. E.,“Electrospray FTMS and MALDI TOF MSCharacterization of a Methyl Silsesquioxane Resin”;Proc. 49th ASMS Conference on Mass Spectrometryand Allied Topics; in press.

Tesk, J. A., “NIST Reference Material for UHMWPE”,Biomaterials Forum, 2001; 22(6):12.

—,“NIST Workshop on Reference Data for the Propertiesof Biomaterials”; Journal of Biomedical MaterialsResearch, Applied Biomaterials, 2001; 58(4).

—,“Reference Data and Materials Needed”; BiomaterialsForum, 2001; 22(6):11.

—,“Reference Materials for Tissue Engineered MedicalProducts” in Tissue Engineering; in press.

VanderHart, D. L., “Solid State NMR Investigation ofParamagnetic Nylon-6 Clay Nanocomposites I.Crystallinity, Morphology and the Direct Influence ofFe(+3) on Nuclear Spins; Chemistry of Materials; inpress.

—, “Solid State NMR Investigation of ParamagneticNylon-6 Clay Nanocomposites II. Measurement ofClay Dispersion, Crystal Stratification and Stability ofOrganic Modifiers; Chemistry of Materials; in press.

VanderHart, D. L.; Asano, A., and Gilman, J. W., “NMRMeasurements Related to Clay-Dispersion Qualityand Organic-Modifier Stability in Nylon-6/ClayNanocomposites”; Macromolecules, 2001; 34:3819–3822.

Wallace, W. E., “Polymeric Materials Interest GroupWorkshop Report”; Proc. 49th ASMS Conference onMass Spectrometry and Allied Topics; in press.

Wallace, W. E.; Fischer, D. A.; Efimenko, K.; Wu, W.-L.,and Genzer, J., “Polymer Chain Relaxation: SurfaceOutpaces Bulk, Brookhaven National LaboratoryNational Synchrotron Light Source 2000 ActivityReport, Technical Highlights”; Brookhaven NationalLaboratory Technical Publication 52615, 2000.

—,“Polymer Chain Relaxation: Surface Outpaces Bulk”;Macromolecules, 2001; 34:5081.

Wallace, W. E. and Guttman, C. M., “Data AnalysisMethods for Synthetic Polymer Mass Spectrometry:Autocorrelation”; Journal of Research of the NationalInstitute of Standards and Technology; in press.

Wallace, W. E.; Guttman, C. M., and Antonucci, J. M.,“Mass Spectroscopy of Spin-on-glass Low-kDielectric Precursors”; Polymer Preprints, 2001;42(1):279–280.

Wallace, W. E.; Guttman, C. M.; Fanconi, B. M., and Bauer,B. J., “MALDI MS of Saturated HydrocarbonPolymers: Polyethylene and Other Polyolefins”; Proc.of the 49th ASMS Conference on Mass Spectrometryand Allied Topics; Chicago, IL; in press.

Wang, G. Z. G.; Wang, H.; Shimizu, K.; Han, C. C., andHsiao, B. S., “Early Stage Crystallization in Poly(Ethylene-co-Hexene) by SAXS/WAXD, DSC, OMand AFM”; ACS, Polymer Materials Science andEngineering, 2001, 85.

Wang, H.; Composto, R. J.; Hobbie, E. K., and Han, C. C.,“Multiple Lateral Length Scales in Phase-SeparatingThin Film Polymer Blends”; Langmuir, 2001; 17:2857–2860.

Wang, H.; Wang, G. Z. G.; Han, C. C., and Hsiao, B. S.,“Simultaneous SAXS and WAXS Study of theIsothermal Crystallization in Polyolefin Blends”; ACS,Polymer Materials Science and Engineering, 2001, 85.

Washburn, N. R.; Simon, C. G.; Tona, A.; Elgendy, H. M.;Karim, A., and Amis, E. J., “Co-extrusion ofBiocompatible Polymers for Scaffolds with ControlledMorphology”; Journal of Biomedical MaterialsResearch; in press.

Weir, M. D.; Khatri, C. A., and Antonucci, J. M., “FacileSynthesis of Hydroxylated Dimethacrylates for Use inBiomedical Applications”; Polymer Preprints, 2001;42(2).

Wetzel, S. J.; Guttman, C. M., and Girard, J. E., “TheInfluence of Laser Energy of MALDI on theMolecular Mass Distribution of Synthetic Polymers”;Proc. of the 49th American Society for MassSpectrometry Conf.; Chicago, IL, 2001.

Publications

61

Wilson, P. T.; Briggman, K. A.; Stephenson, J. C.; Wallace,W. E., and Richter, L. J., “Molecular Order at PolymerInterfaces Measured by Broad-BandwidthVibrationally-Resolved Sum-Frequency GenerationSpectroscopy”; Quantum Electronics and LaserScience Conference 2001 Technical Digest; in press.

Wu, W.-L.; Lin, E. K.; Lin, Q. H., and Angelopolous, M.,“Small-Angle Neutron Scattering Measurements ofNanoscale Lithographic Features”; Journal of AppliedPhysics, 2000 Dec 15; 88(12):7298–7303.

—,“Small-Angle Neutron Scattering Measurements ofNanoscale Lithographic Features”; Polymer Preprints,2001; 42(1):265–266.

Xu, H. H. K.; Quinn, J. B.; Smith, D. T.; Antonucci, J. M.;Schumacher, G. E., and Eichmiller, F. C., “Dental ResinComposites Containing Silica-Fused Whiskers:Effects of Whisker-to-Silica Ratio on FractureToughness and Indentation Properties”; Biomaterials;in press.

Yang, S.; Mirau, P.; Pai, C. S.; Nalamasu, O.; Reichmanis,E.; Lin, E. K.; Lee, H. J.; Gidley, D.; Frieze, W. E.; Dull,T. L.; Sun, J., and Yee, A. F., “Design of NanoporousUltra Low-Dielectric Constant Organosilicates by Self-Assembly”; ACS PMSE, 2001.

Yang, S.; Pai, C. S.; Nalamasu, O.; Reichmanis, E.; Mirau,P.; Obeng, Y. S.; Seputro, J.; Lin, E. K., and Lee, H. J.,“Design of a Nanoporous Ultra Low-DielectricConstant Organosilicate”; Proc. of the 7th Intl. Conf.on Polymers in Electronic Packaging, 2001.

Zhang, Y.; Douglas, J. F.; Ermi, B. D., and Amis, E. J.,“Influence of Counterion Valency on the ScatteringProperties of Highly Charged PolyelectrolyteSolutions”; Journal of Chemical Physics, 2001;114:3299-3313.

62

Polymers Division

ChiefEric J. Amis

Phone: 301-975-6762E-mail: [email protected]

Deputy ChiefBruno M. Fanconi


NIST FellowCharles C. Han


Group Leaders

Electronics MaterialsWen-Li Wu


BiomaterialsFrancis W. Wang


Multiphase MaterialsCharles Han

Multivariant Measurement MethodAlamgir Karim


Characterization and MeasurementMethod Development

Wen-li Wu Standards and Data

Bruno FanconiInternal CapabilitiesEric J. Amis, Acting

Processing CharacterizationKalman Migler


63

Research Staff

Amis, Eric [email protected]

Neutron, x-ray and light scatteringPolyelectrolytesViscoelastic behavior of polymersDendrimers and dendritic polymersFunctional biomaterials

Antonucci, Joseph [email protected]

Synthetic and polymer chemistryDental composites, cements and adhesionInitiator systemsInterfacial coupling agentsRemineralizing polymer systems

Ashley, Karen+

[email protected] thin filmsDewettingCombinatorial measurements

Balizer, Edward+

Neutron, x-ray scatteringPolymer electrostriction

Barnes, John D.+

[email protected] and vapor transport in polymersX-ray scatteringComputer applications in polymer measurements

Bauer, Barry [email protected]

Polymer synthesis thermal characterizationNeutron, x-ray and light scatteringDendrimers, metallic ions nanocluster

Beers, [email protected]

Crystallization in thin filmsOptical light scatteringControlled/living polymerizations

Blair, William [email protected]

Polymer analysis by size exclusionChromatographyMass spectrometry of polymers

Bowen, Rafael L.*[email protected]

AdhesionDental compositesNovel monomer synthesis

Brunner, [email protected]

Mass spectrometry of polymersChemical modificationInfrared spectroscopy

Bur, Anthony [email protected]

Dielectric properties of polymersFluorescence and optical monitoring of polymer

processingPiezoelectric, pyroelectric polymersViscoelastic properties of polymers

Cantoni, Giovana+

[email protected] and biopolymersPolymer thin filmsTissue engineering

Carey, Clifton M.*[email protected]

Dental plaqueMicroanalytical analysis techniquesPhosphate chemistryIon-selective electrodes

Chang, Shu Sing+

Thermal properties of polymeric and compositematerials

Composite process monitoringElectronic packaging materialsPolymer phase transitionsPrecision electrical and temperature measurements

Chen, Erqiang+

[email protected] morphologyPhase behavior of block copolymersPolymer blends

Research Staff

64

Chen, Wei+

[email protected] and neutron scatteringLow dielectric constant material characterization

Cherng, Maria*[email protected]

Calcium phosphate biomaterials

Chiang, Chwan [email protected]

Electroluminescent polymersResidual stressImpedance spectroscopy

Chiang, Martin [email protected]

Computational mechanics (finite element analysis)Strength of materials, fracture mechanicsEngineering mechanics of polymer-based materialsBi-material interface

Chow, Laurence C.*[email protected]

Calcium phosphate compounds and biomaterialsDental and biomedical cementsSolution chemistryTopical dental fluorides

Crosby, [email protected]

Polymer adhesionPolymer fractureViscoelasticityElastomersBlock copolymers

Dähnhardt, Jan-Erik+

Self-curing dental repair resin

Davis, G. Thomas+

[email protected] packagingPolymer crystallizationX-ray diffraction of polymersPolarization distributionPiezoelectricity in polymers

DeReggi, Aime [email protected]

Polarization-depth profiles in polymersSpace charge in dielectricsFerroelectric polymersPolymeric piezo- & pyroelectric devices

Dickens, Sabine*[email protected]

Dental compositesDental adhesivesTransmission electron microscopy

Di Marzio, Edmund A.+

[email protected] mechanics of polymersPhase transitionsGlassesPolymers at interfaces

Douglas, Jack [email protected]

Theory on polymer solutions, blends, and filledpolymers

Transport properties of polymer solutions andsuspensions

Polymers at interfacesScaling and renormalization group calculation

Dunkers, Joy [email protected]

Optical coherence tomographyImage analysisFiber optic spectroscopyInfrared microspectroscopy of polymers

Eanes, Edward D.+

[email protected] of bones and teethCalcium phosphate compounds as dental materialsEffects of solution and biological molecules on

precipitation of calcium phosphatesLiposome studies

Eichmiller, Frederick C.*[email protected]

Clinical dentistryCompositesDentin adhesives

Eidelman, Naomi N.*[email protected]

Prevention of calcification in the cardiovascularsystem

Effect of phosphonates, cholesterol andphospholipids on calcium phosphate formation

Characterization of calcified deposits by FTIRmicroscopy

Esker, Alan R.+

[email protected] mediated polymer interdiffusionPhase separation kinetics of polymer blends

Research Staff

65

Fanconi, Bruno [email protected]

Infrared & Raman spectroscopy of polymersStructure of polymersPolymer fractureProcess monitoring of polymer composites

Feresenbet, Elias+

Silane depositionComposite interfaces

Flaim, Glenn M.*[email protected]

Fabricating dental composites

Floyd, Cynthia J. E.+

[email protected] composites

Flynn, Kathleen [email protected]

Permeability measurements and databaseFlow visualization experimentsWeb page development

Fowler, Bruce O.+

[email protected] and Raman spectroscopyStructure of calcium phosphates, bones, and teethComposites

Frukhtbeyn, Stanislav+

Calcium phosphate compounds and biomaterialsTopical dental fluorides

Galvin, Agnes Ly.*[email protected]

Clinical dental assistantAdhesion measurements

George, Laurie A.*[email protected]

Glass-ceramics

Giuseppetti, Anthony A.*[email protected]

Casting of dental alloysMercury-free amalgam alterative

Goldschmidt, Robert+

[email protected] spectrometry of polymersChemical analysis

Groehn, Franziska+

[email protected] and x-ray scatteringElectron microscopyDendrimersNanocompositesNanocrystalsOrganic-inorganic hybrids

Guttman, Charles [email protected]

Solution properties of polymersSize exclusion chromatographyMass spectroscopy of polymers

Han, Charles [email protected]

Phase behavior of polymer blendsPhase separation kinetics of polymer blendsPolymer characterization and diffusionShear mixing/demixing and morphology control

of polymer blendsStatic, time resolved, and quasi-elastic scattering

of light and neutron

Hedden, [email protected]

Siloxane polymers: synthesis and properties ofmonomers, linear chains, and networks

Mechanical properties of elastomersPolymer fractionationGel permeation chromatography

Hobbie, Erik [email protected]

Light scattering and optical microscopyDynamics of complex fluidsShear-induced structures in polymer blends and

solutions

Holmes, Gale [email protected]

Composite interface scienceChemical structure-mechanical property

relationships for polymersPolymer chemistryMass spectroscopy

Research Staff

66

Hunston, Donald [email protected]

Adhesion science and technologyFracture behavior of polymersProcessing and failure behaviors of polymer

compositesFlow behavior of dilute high-polymer solutionsMacromolecular-small molecule bindingHybrid-reinforced composites

Hussain, Latiff*[email protected]

Monomer polymer synthesis, characterization,testing

Dental composites, adhesives

Jeon, Hyun Sik+

[email protected] light scattering and optical microscopyStructure and morphology of two-phase elastomer

blends under shear

Jianmei, He+

[email protected] mechanics (finite element modeling)Adhesive jointsStructural optimization

Jones, Ronald+

[email protected] and x-ray scatteringNeutron reflectivityPolymer surfaces and thin filmsPolymer phase transitions and computer simulation

Karim, [email protected]

Polymer fillers and nanocompositesPatterning of thin-polymer blend films on

inhomogenous surfacesNeutron and x-ray reflection, scattering,AFM and optical microscopyThin-film phase behavior of polymer blendsCombinatorial thin-film polymer coatings

Kelly, J. Robert+

[email protected] phosphate cementsDental ceramicsFailure analysis; dental prosthesesFinite element analysisWeibull analysis

Kennedy, Scott B.+

[email protected] engineeringBiomaterialsBlock copolymersCombinatorial surface patterns

Kennedy, Sharon [email protected]

Lithographically patterned surfacesBiomaterialsCombinatorial patterned arraysCombinatorial polymer blendsCombinatorial phase behavior of polymer blends

Khatri, Chetan A.+

[email protected]/polymer synthesis and characterization

Khoury, Freddy [email protected]

Crystallization, structure and morphology ofpolymers

Analytical electron microscopy of polymersWide-angle and small-angle x-ray diffractionStructure and mechanical property relationships

Kumar, Sanat+

[email protected] coatings and thin filmsSimulationsPhysical properties of polymersPhase separationMultiphase polymer systems

Lee, Hae-Jeong+

[email protected] reflectivitySmall-angle neutron scatteringSynthesis and characterization of low dielectric

constant thin films

Lenhart, Joseph [email protected]

SensorsInterphase structure

Li, Bizhong+

Polymer processingPolymer blendsPolymer-clay processing

Liao, Nam S.*[email protected]

Synthesis and testing of dental adhesivesInternal stress of composition due to polymerization

Research Staff

67

Lin, Eric [email protected]

Statistical mechanicsX-ray and neutron reflectivity

Liu, [email protected]

Polymer synthesisThermal gravimetric analysisDifferential scanning calorimetryGel permeation chromatographyInfrared spectroscopyNuclear magnetic resonanceScanning electron microscopyAtomic force microscopy

Lynn, Gary W.+

[email protected] and neutron reflectivityOptical microscopy

Mager, Carie+

[email protected] bioceramicsFracture mechanics

Markovic, Milenko*[email protected]

Calcium phosphate chemistryBiomineralization (normal and pathological)Crystal growth and dissolution kineticsHeterogeneous equilibria

Mathew, Mathai*[email protected]

CrystallographyCalcium phosphate compounds

Maurey, John M.+

[email protected] light scatteringOsmometryDensimetryRefractometryIntrinsic viscosity

McDonough, Walter [email protected]

Processing and cure monitoring polymer compositesFailure and fracture of polymersPolymer composite interfaces

McKenna, Gregory B.+

[email protected], yield and fracture of polymersNonlinear viscoelasticityMolecular rheologyPhysics of polymer glassesRubber thermodynamics and mechanicsMechanics of composites

Meredith, J. Carson+

[email protected] polymer blendsPhase-separation and wetting properties of thin

filmsCombinatorial methods for coatings

Migler, [email protected]

Effects of shear and pressure on phase behaviorFluorescence and optical monitoring of polymer

processingLiquid crystalsShear-induced two phase structuresPolymer slippage

Mopsik, Frederick I.+

[email protected] measurements and behaviorAutomated measurement designComputerized data analysis and programmingElectrical properties of polymers

Mueller, Herbert J. *[email protected]

Dental biomaterialsInterfacial interactions via electrochemical and

infrared spectroscopyChevron notch fracture toughnessMechanical properties via nondestructive methods

Nakatani, Alan I.+

[email protected] blends and solution properties under shearSmall-angle neutron scatteringPhase behavior of polymer blendsFilled polymersRheo-optical behavior of polymers

Noda, Natsuko+

[email protected] spectroscopyDielectric characterization of composites

Research Staff

68

Nozaki, Ryusuke+

[email protected] relaxation in polymersImpedence spectroscopy

Obrzut, [email protected]

Electronic properties of polymers and compositesPhotoelectron spectroscopy (x-ray and UV)Dielectric relaxation spectroscopyElectronic packagingReliability, stress testingMicrowave and optical waveguides

Parry, Edward E.*[email protected]

Dental appliance and crown and bridges fabricationMachine shop applications

Pathak, Jai A.+

[email protected] rheologyPolymer dynamicsGlass transitionPolymer blends

Pfeiffer, Carmen+

[email protected] resinsMonomer synthesis

Phelan, Jr., Frederick [email protected]

Resin transfer molding: modeling and processingstudies

Viscoelastic flow modelingFlow in porous mediaLattice Boltzmann methods

Pochan, Darrin+

[email protected] & TEM of polymeric materialsWide-angle and small-angle x-ray scatteringBlock copolymer phase behavior

Popielarz, Roman+

[email protected] synthesis and characterizationPhoto-polymerization

Qiao, Fang+

Polymer mixing and compoundingLiquid crystalline polymer/thermal plastic polymer

mixing

Roth, Steven [email protected]

Piezoelectric polymer transducers-fabrication andapplications

Vacuum deposition of metalsCalibration of polymer transducersMicrocomputer interfacingFluorescence measurements

Schmidt, Gudrun+

[email protected] blendsLiquid crystalline polymersPolymer-clay interactionLight and neutron scattering

Schultheisz, Carl [email protected]

Failure of compositesExperimental mechanicsTorsional dilatometryPhysics of polymer glassesPolymer rheology

Schumacher, Gary E.*[email protected]

Clinical dentistryCompositesDentin adhesives

Sehgal, Amit+

[email protected], cell-surface biophysicsPolymer thin filmsPolyelectrolytes and conducting polymersStructure and dynamics of polymer solutionsLight scattering and fluorescence photobleaching

recovery

Shi, An-Chang +

[email protected] theoryPolymer phase transitions

Sieck, Barbara A.*[email protected]

Calcium phosphate compoundsChemical analysisRemineralization

Simon, Carl G., [email protected]

BiocompatibilityCytotoxicitySignaling in human plateletsBone marrow cell lineage/trafficking

Research Staff

69

Skrtic, Drago*[email protected]

Calcium phosphates as dental materialsLiposome studies

Smith, Archie+

[email protected] (high-throughput) experimental

design and developmentPolymer crystallization behaviorThin-film block copolymer behaviorNanofilled polymer behaviorElectron, atomic force, x-ray and light microscopies

Snyder, Chad [email protected]

Polymer crystallizationWAXD and SAXS of polymeric materialsThermal expansion measurementsThermal analysis of polymersDielectric measurements and behavior

Soles, [email protected]

Viscoelastic properties of polymersElastic and inelastic neutron scatteringX-ray and neutron reflectivitiesPolymer thin films

Son, Younggon +

[email protected] processingPolymer phase behaviorInterfacial phenomena

Stafford, Christopher+

[email protected] adhesionSurfaces and interfacesPolymer thin films

Stansbury, Jeffrey [email protected]

Synthetic chemistryPolymers and polymer compositesPolymerization of expanding monomersFluorinated polymersPolymerization kinetics

Starr, [email protected]

Dynamics of filled polymersSlow dynamics in soft condensed matterMolecular dynamics simulations and parallel

computing

Takagi, Shozo*[email protected]

CrystallographyX-ray diffractionCalcium phosphate biomaterialsTopical fluoridationDe- and remineralization

Tesk, John [email protected]

Biomaterials: industrial relationsBond strength characterizationCasting of alloysStrength of dental systemsThermal expansion and properties of dental materialsFinite element studiesPorcelain-metal systemsWeibull analysisWear testing, orthopaedic materialsReference biomaterials

Tung, Ming S.*[email protected]

Chemistry of calcium phosphate compoundsRemineralization studiesStandard reference materials

VanderHart, David [email protected]

Measurement of orientation in polymer fibers and films

Solid-state NMR of polymersMeasurement of polymer morphology at the

2–50 nm scalePulsed field gradient NMR

Van Zanten, John H.+

[email protected] fluidsPolymer interfacesScattering of light, neutrons & x raysBiophysicsInterfacial phenomenaScanning-probe microscopy

Vogel, Gerald L.*[email protected]

Dental plaque chemistry, chemistry of calciumphosphates

Microanalytical techniques

Research Staff

70

Wallace, William [email protected]

Surface and interface behaviorIon beam and electron spectroscopiesX-ray and neutron reflectivityMALDI mass spectrometry

Wang, Francis [email protected]

Photophysics and photochemistry of polymersFluorescence spectroscopyCure monitoring of polymerizationTissue engineering

Wang, Howard +

[email protected] phase transitions in polymerWetting, segregation and transport in polymerStructure and dynamics in polymer gels

Washburn, [email protected]

Tissue engineeringPolymer blendsBiomaterial interfacesViscoelastic properties of polymers

Weaver, Alia+

[email protected] spectrometry of polymers

Weir, [email protected]

BiomaterialsTissue engineeringBiodegradable hydrogelsCombinatorial analysisUV and fluorescence spectroscopy of polymers

Wetzel, [email protected]

Mass spectrometry of polymersData analysisChemometrics

Wu, [email protected]

Neutron and x-ray scattering and reflectivityElectron microscopyMechanical behavior of polymers and compositesPolymer surfaces and interfaces

Yurekli, Koray+

[email protected] nanocompositePhase separationThin films and interfacesNeutron and light scattering

Xie, Baosheng+

Testing micro tensile and micro-sheer bond strength

Xu, Huakun*[email protected]

Silver alloy alternative to amalgamWear and fatigueFiber and whisker reinforcement

Zhang, Yubao+

[email protected] light scatteringPolyelectrolytesSmall-angle neutron scattering

*Research Associate+Guest Scientist

71

Organizational Charts

Materials Science and Engineering Laboratory

L.E. Smith, DirectorD.E. Hall, Deputy Director

CeramicsS.W. Freiman, Chief

S.J. Dapkunas, Deputy

Materials ReliabilityF.R. Fickett, Chief

T.A. Siewert, Deputy

NIST Center forNeutron ResearchJ.M. Rowe, Director

National Institute of Standards and Technology

DirectorBoulder Laboratories

Director forAdministration& Chief Finan-

cial Officer

TechnologyServices

AdvancedTechnology

Program

ManufacturingExtension

Partnership

ManufacturingEngineeringLaboratory

ChemicalScience andTechnologyLaboratory

MaterialsScience andEngineeringLaboratory

Electronics andElectrical

EngineeringLaboratory

InformationTechnologyLaboratory

PhysicsLaboratory

Building andFire ResearchLaboratory

PolymersE.J. Amis, Chief

B.M. Fanconi, Deputy

Baldrige NationalQuality Award

DirectorDeputy Director

MetallurgyC.A. Handwerker, Chief

F.W. Gayle, Deputy

72

Organizational Charts

Polymers Division (854.00)Eric Amis, Division Chief

Bruno Fanconi, Deputy ChiefDonna Stutso, Administrative Officer

Dawn Bradley, Division SecretarySheila St.Clair, Office Automation Assistant

Characterization & Measurement (854.01)Bronny Webb, Secretary

Method DevelopmentWen-li Wu

M. ByrdM. ChiangJ. DunkersR. HeddenR. JonesF. LandisJ. Lenhart

S. Lin-GibsonF. Starr

W. Wallace

Standards & DataBruno Fanconi

W. BlairC. Guttman

C. SchultheiszJ. Tesk

L. BrunnerR. Goldschmidt

J. MaureyA. WeaverA. Wetzel

Internal CapabilitiesEric Amis, Acting

B. BauerA. DeReggiJ. DouglasS. HudsonF. Khoury

D. LiuW. McDonoughP. McGuigganD. Vanderhart

Electronics Materials (854.02)Wen-li Wu, Group LeaderBronny Webb, Secretary

Biomaterials (854.03)Francis Wang, Group Leader

June Burton, Secretary

Multiphase Materials (854.04)Charles Han, NIST Fellow

June Burton, Secretary

Processing Characterization(854.05)

Kalman Migler, Group LeaderKaren Hollingsworth, Secretary

Multivariant MeasurementMethods (854.06)

Alamgir Karim, Group LeaderKaren Hollingsworth, Secretary

H. LeeN. Noda

R. PopielarzW. Sakai

C. ChiangE. Lin

J. ObrzutC. SnyderC. Soles

J. AntonucciJ. Hsii

C. SimonM. Weir

M. FarahaniB. FowlerC. Khatri

A. MizukamiN. Yamamoto

S. Yoneda

A. BurK. FlynnS. Roth

J. PathakY. Son

E. HobbieG. Holmes

D. HunstonF. Phelan

E. FeresenbetJ. He

H. KimC. Moon

G. SchmidtK. ShimizuH. WangZ. Wang

K. BeersA. Crosby

S.L. KennedyN. Washburn

K. AshleyG. Cantoni

S.B. KennedyA. SehgalA. SmithK. Yurekli

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