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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites

12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron

Stabilization of polystyrene/polylactic acid cocontinuous blends by interfacial graphene

Lian Bai1, Siyao He2, John W. Fruehwirth1, Xiang Cheng*1, Christopher W. Macosko*1

1. Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Ave. SE, Minneapolis,Minnesota 55455, United States

2. Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States

Reduced graphene oxide (r-GO) is known to be effective in increasing the conductivity of cocontinuous polymer blends with a lower electrical percolation threshold. However, little is known regarding the localization and dynamics of r-GO along with morphology change during annealing. In this study, we develop a facile method to stabilize the polystyrene (PS)/polylactic acid (PLA) cocontinuous blends with r-GO jammed at interface. In this method, the non-functionalized GO is premixed with PLA via solvent method, and then reduced in-situ at 210oC to obtain a PLA/r-GO masterbatch. This masterbatch is further mixed with PS via batch melt compounding to obtain the PLA/PS/r-GO ternary nanocomposite. We observe the migration of r-GO from the PLA phase to the interface during annealing. The interfacial r-GO suppresses the coarsening of cocontinuous morphology and increases the conductivity of the filled polymer blend. Moreover, we systematically investigate the relationship between r-GO localization, rheological and conductivity change during annealing of r-GO filled PLA/PS cocontinuous blends.

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Covalent Modification of Bulk Carbon Nanotube Materials for Improved Tensile Properties

James S. Baker1,2 ; Michael A. Meador1

1 NASA-Glenn Research Center, Cleveland, Ohio; 2 NASA Postdoctoral Program Fellow

Carbon nanotubes (CNT) have attracted a great deal of interest as reinforcement in composite materials due to their exceptional mechanical properties. However, less than ideal tensile properties are obtained in composites using bulk CNT materials as the reinforcement. This is due in part to relatively weak inter-CNT and CNT-matrix interactions leading to poor load transfer through the material.

Our group has examined covalent functionalization of the CNT as a means to improve the tensile properties of both bulk CNT materials (sheets, yarns) and the polymer-CNT composites prepared using these functionalized CNTs. Functionalizations examined include: epoxidation (Epox-CNT), aliphatic amine (ApA-CNT), and aromatic amine (ArA-CNT). ApA-CNT functionalized sheet offered the greatest enhancement in sheet tensile properties, with a specific tensile strength of 265 MPa/(g/cm3) compared to 127 MPa/(g/cm3) for the unmodified sheet. Specific tensile modulus was increased to 4.9 GPa/(g/cm3), compared to 0.78 GPa/(g/cm3) for the unmodified material.

Carbon nanotube sheet material was used as a “drop-in” substitute for carbon fiber in the preparation of 60/40 wt% CNT/epoxy resin composites. While the tensile strength of composites using the functional CNT was not significantly improved relative to those using non-modified CNT, composites using the Epox-CNT and ArA-CNT exhibited tensile modulus improvements of 90% and 160%, respectively, relative to the non-modified composites. Strain at failure for the Epox-CNT and ArA-CNT composites was 11% and 3.6%, compared to 27% for the non-modified CNT composite. This presentation will highlight our efforts to improve the tensile properties of CNT sheet and composites obtained using these functionalized materials.

2



Mechanical Characterization and Modeling of Rate Dependent Toughened Structural

Adhesives

Erol Sancaktar, Gamze Sultan Bas

University of Akron, Polymer Engineering Department, Akron, USA 44325

Structural adhesives such as toughened epoxy adhesives are excellent candidates to be used as

impact-resistant adhesives and play an important part in the design of light-weight structures. They

poses energy absorption capability for the endurance of framework to be crashworthy. These

particular properties provide safer conditions for the driver and passengers against the crash effects

in case of accident of automobiles.

In this work, epoxy formulations which contain various combinations of toughening agents have

been characterized to predict rate dependent physical properties by using tensile testing with high

elongation strain gauges at rates varying between 25 and 500 mm/min crosshead rate. Hereby

tensile strength, failure strain and toughness of those structural epoxy adhesives have been

modeled as a function of loading rate by using Ludwik-type equations, and the results compared

with results obtained using Hopkinson Pressure Bar apparatus at different but high speeds

representing impact speeds.

3



Gluing Soft Interfaces by Nanoparticles

Zhen Cao, Andrey Dobrynin

Abstract: Using a combination of the molecular dynamics simulations and scaling analysis we studied

reinforcement of interface between two soft gel-like materials by spherical nanoparticles. Analysis of the

simulations shows that the depth of penetration of a nanoparticle into a gel is determined by a balance of

the elastic energy of the gel and nanoparticle deformations and the surface energy of nanoparticle/gel

interface. In order to evaluate work of adhesion of the reinforced interface, the potential of mean force for

separation of two gels was calculated. These simulations showed that the gel separation proceeds through

formation of necks connecting nanoparticle with two gels. The shapes of the necks are controlled by a

fine interplay between nanoparticle/gel surface energies and elastic energy of the neck deformation. Our

simulations showed that by introducing nanoparticles at soft interfaces, the work required for separation

of two gels could be 10-100 times larger than the work of adhesion between two gels without nanoparticle

reinforcement. These results provide insight in understanding the mechanism of gluing soft gels and

biological tissues by nano- and micro-sized particles.

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High Loading, Dispersion and Stabilization of MWCNT in Epoxy Prepolymers from Continuous High Shear

Reactor Processing

Brian M. Greenhoe, Jeffrey S. Wiggins1

School of Polymers and High Performance Materials, University of Southern Mississippi

118 College Drive #5050, Hattiesburg, MS 39406

Abstract

This manuscript describes a one-step continuous reaction method for preparing large volumes of multiwall carbon

nanotube (MWCNT) reinforced tetraglycidyl-4, 4’-diaminodiphenylmethane prepolymers at nanotube loading up to

26% wt/wt. The continuous reactor was designed based on a co-rotating intermeshing twin screw extruder where the

reactor barrels were modified into two sections, hot and cold zones. Hot zone temperature was set at 160 to 200 °C

and designed for the partial curing of the epoxy resin to build viscosity while the cold zone was maintained between

room temperature and 100 °C to quench the reaction and enhance MWCNT dispersion. Differential scanning

calorimetry and rheological analysis were used to demonstrate the cure conversion, glass transition temperatures,

and viscosity of epoxy prepolymers can be finely tuned through the adjustment of hot zone temperature. Optical

microscopy and transmission electron microscopy indicated that the nanotube dispersion was greatly improved at

lower cold zone temperatures due to the increased shear states imposed by an increased resin viscosity. Bulk

electrical conductivity obtained by four point probe analysis was used as an indirect qualification of dispersion state

and conductivities of up to 0.84 S/cm were obtained.

† Equally contributing author 1Corresponding author. Tel.: +1 601 266 6960; Fax: +1 601 266 5635. E-mail address: [email protected] (Jeffrey Wiggins)

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mailto:[email protected]



Failure of Tube Models to Predict the Linear Rheology of Star/Linear Blends

RYAN HALL, University of Michigan, PRIYANKA DESAI, University of Michigan,

BEOMGOO KANG, University of Tennessee, MARIA KATZAROVA, Illinois Institute of

Technology, QIFAN HUANG, University of Michigan, SANGHOON LEE, Pohang University

of Science and Technology, TAIHYUN CHANG, Pohang University of Science and

Technology, DAVID VENERUS, Illinois Institute of Technology, JIMMY MAYS, University of

Tennessee, JAY SCHIEBER, Illinois Institute of Technology, RONALD LARSON, University

of Michigan

We compare predictions of two of the most advanced versions of the tube model, namely the

“Hierarchical model” by Wang et al. (J. Rheol. 54:223, 2010) and the BOB (branch-on-branch)

model by Das et al. (J. Rheol. 50:207-234, 2006), against linear viscoelastic data on blends of

monodisperse star and monodisperse linear polybutadiene polymers. The star was carefully

synthesized/characterized by temperature gradient interaction chromatography, and rheological

data in the high frequency region were obtained through time-temperature superposition. We

found massive failures of both the Hierarchical and BOB models to predict the terminal

relaxation behavior of the star/linear blends, despite their success in predicting the rheology of

the pure star and pure linear. This failure occurred regardless of the choices made concerning

constraint release, such as assuming arm retraction in “fat” or “skinny” tubes, or allowing for a

“disentanglement relaxation” even to cut off the constraint release Rouse process at long times.

The failures call into question whether constraint release can be described as a combination of

constraint release Rouse processes and dynamic tube dilation within a canonical tube model of

entanglement interactions.

6



Reinforcement of Polyamide 6 with cellulose nanocrystals prepared via in-situ ring

opening polymerization: thermal, mechanical and rheological properties

Shahab Kashani Rahimi and Joshua U. Otaigbe,

School of Polymers and High Performance Materials, University of Southern Mississippi

118 College Drive, Hattiesburg, MS, USA

Novel class of polyamide 6 nanocomposites reinforced with cellulose nanocrystals were prepared by in-situ ring-

opening polymerization followed by melt extrusion with the CNC content ranging from 1-3 wt% in the matrix. The

effects of CNC content and of surface modification with organosilane coupling agent on thermal, mechanical and

melt rheological properties of these systems were systematically studied. Solid state NMR analysis confirmed the

formation of interfacial bond between the matrix and the surface of CNC through two different mechanisms namely

the re-propagation of polyamide chains through surface initiated anionic species and transamidation reaction. The

thermal analysis results revealed that the CNC significantly impeded the spherulitic crystal growth rate of the

polyamide chains that is associated with reduction in crystallinity. The surface modified CNC particles were found

to enhance the promotion of γ-type crystals which is associated with the interfacial bond formation on the particle

surface. The mechanical properties of the polyamide matrix were found to be enhanced by addition of the CNC

while the SEM images of the fractured surface showed that a significant interfacial plastic deformation occurred

when using the surface modified particles. The reinforcing effect of the CNCs is confirmed by the observed increase

in tensile modulus and strength. The melt rheological analysis showed significant changes in flow behavior of these

systems both in steady and oscillatory modes, confirming the evolution of the samples structure. This novel method

of reinforcing high-melting engineering thermoplastics by renewable cost effective cellulosic fibers through in-situ

reactive polymerization opens up a new opportunity towards development of novel functional high performance

composite materials reinforced with small fraction of environmentally-friendly fibers for a number applications

where traditional fiber-reinforced polymer composites are not useable.

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Relaxation Dynamics of Nanoparticle-Tethered Polymer Chains

Sung A Kim,†, § Rahul Mangal,† and Lynden A. Archer†

†School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York

14853, United States

§Department of Chemical Engineering and Materials Science, University of Minnesota,

Minneapolis, Minnesota 55455, United States

This talk presents the relaxation dynamics of nanoparticle-tethered cis-1,4-polyisoprene (PI)

investigated using rheometry and dielectric spectroscopy. By densely grafting polymer chains to

spherical nanoparticles, this self-suspended suspension is a model platform to study the effects of

surface and geometrical confinement on the chain configuration and dynamics from the

experiments performed in bulk materials. We find that tethered polymer molecules relax more

slowly and generally form more extended chain configurations than their untethered

counterparts. At a fixed grafting density, increasing the PI molecular weight up to values close to

the entanglement molecular weight speeds up chain relaxation dynamics and decreases the

degree of chain stretching when compared to untethered chains. Decreasing the polymer grafting

density for a fixed molecular weight has the opposite effect. It dramatically slows down chain

relaxation, increases interchain coupling, and leads to a transition in rheological response from

simple fluid behavior to jammed, soft-glassy rheology. Higher measurement temperature

produces more jamming, more intense chain stretching, and speed-up of molecular relaxation at

a rate that decreases with grafting density and molecular weight. Our observations are explained

in terms of chain confinement driven by crowding between particles and the space filling

constraint on chains tethered to nanoparticles in self-suspended materials.

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VOLUMETRIC PROPERTIES AND STRAIN PERFORMANCE OF GLASSY AMORPHOUS POLYMER NETWORKS

Kyler R. Knowles, Jeffrey S. Wiggins School of Polymers and High Performance Materials, The University of Southern Mississippi

118 College Drive #5050 Hattiesburg, MS 39401

Processing carbon fiber composite laminates creates molecular-level strains in the thermoset matrix upon curing and cooling which can lead to shape deformations, micro-cracking, and other issues. The origin of these strains lies in the properties of the polymer matrix, which experiences significant changes in volume and physical state throughout the curing process. In this study, two glassy amorphous high-Tg polymer networks were formulated to be chemically-similar while differing in crosslink density. Tetraglydicyl-4,4’-diamino-diphenyl methane and diglycidyl ether of bisphenol-F were combined with 3,3’-diaminodiphenyl sulfone to examine the effect of crosslink density on key properties which dictate strain creation in composites manufacturing. Volumetric properties such as chemical shrinkage and coefficient of thermal expansion were quantified using high-pressure mercury dilatometry and thermomechanical analysis, respectively. Increased crosslink density corresponds with a decrease in both chemical shrinkage and coefficient of thermal expansion. Additionally, a non-contact, full-field strain measurement technique known as digital image correlation was used for strain analysis, allowing for observation of anelastic strain recovery after loading in compression and correlation with matrix volumetric properties.

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DNA as a Flame Retardant Additive for Low-Density Polyethylene

Parker W. Leea, Sergey A. Isarova, Jenna H. Towsleea, Kathleen M. Hoffmanb, Rick D. Davisb,

João M. Maiaa, and Jonathan K. Pokorskia,*

aDepartment of Macromolecular Science and Engineering, School of Engineering, Case Western

Reserve University, Cleveland, OH, 44106, USA bFire Research Division, Engineering Laboratory, National Institute of Standards and

Technology, Gaithersburg, MD, 20899, US

The need for alternatives to classic halogenated and metal oxide flame retardant additives

has increased in the past 40 years due to environmental concerns and high loading levels

respectively. Intumescent organic flame retardants, such as melamine polyphosphate (MPP) and

ammonium polyphosphate (APP), have been used to fill this need as they can provide flame

retardant properties at lower loading levels than metal oxides. However, there are environmental

and biological concerns over the use of MPP and APP as additives. Deoxyribonucleic acid

(DNA) has been recently shown to act as an effective flame retardant when applied as a coating

to cotton fabrics and compounded with polyethylene-co-vinyl acetate, however it has not yet

been applied to commodity thermoplastics.

This study expands the use of DNA as a flame retardant by studying the properties of

low-density polyethylene (LDPE) when compounded with DNA. LDPE is one of the most

widely used commercial thermoplastics and has very poor flame retardant performance. A

systematic study was performed on the effect of DNA loading level on flame retardant

performance with MPP used as a comparator. The compounding torque, mechanical properties,

dispersion, and biochemical properties of DNA/LDPE materials were studied to determine the

compatibility and state of DNA after compounding. The results indicate that DNA has better

flame retardant properties than MPP at lower loading levels and maintains better mechanical

properties. This study is the first to utilize DNA as a flame retardant additive with LDPE and

expands the utility and understanding of DNA during compounding with commodity

thermoplastics.

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Abstract: We study mechanical properties of polymeric nanocomposites with liquid

inclusions in polymer network matrix using molecular dynamics simulations. The

shear modulus of nanocomposite is shown to be a function of the elastocapillary

number γSL/(GNR0), where γSL is the surface tension of network/liquid interface, GN is

the shear modulus of network and R0 is the initial size of the liquid inclusion. First, in

the range of elastocapillary numbers, γSL/(GNR0) << 1, the composite shear modulus

increases with increasing this parameter value. In this interval of elastocapillary

numbers, the liquid inclusion softens the network such that the composite modulus

Gcomp is smaller than GN. This is in agreement with the classical Eshelby's inclusion

theory. However, for elastocapillary numbers, γSL/(GNR0) ≈ 1, the shear modulus of

composite is comparable to that of the network, Gcomp ≈ GN. In this range of

parameters, the surface energy gained from the deformed liquid inclusion

compensates for the elastic energy lost by replacing network with liquid. When the

elastocapillary number increases further, γSL/(GNR0) >> 1, the interfacial energy of

network/liquid interface dominates the mechanical response of the composite.

Analysis of the shape of the liquid inclusion shows that the inclusion stays spherical

under this situation. Under this situation, the liquid inclusion behaves like a

nanoparticle, acts as a stress concentrator and stiffens the network. The classical

Eshelby's inclusion theory fails to explain this phenomenon. We apply a new

continuum mechanics model of this class of nanocomposite materials to explain this

unusual mechanical response of nanocomposite materials.

Mechanical Properties of Polymeric Nanocomposites with Liquid Inclusions

Authors: Zhen Cao, Andrey Dobrynin, Heyi LiangThe University of Akron

11



Rheology and Dynamics of Spherical Motifs in Ordered Self-assembly

Gengxin Liu, Xueyuan Feng, Dong Guo, Wei Zhang, Stephen Z.D. Cheng

Diverse ordered structure can be formed by the self-assembly of “giant surfactants”,

macromolecular amphiphiles with precise chemical structures and containing shape-persistent

molecular nanoparticles. Although not entangled in the common sense, they present

intriguing viscoelastic properties comparing to block copolymers. The rheology and

dynamics of “giant surfactants” in disordered states and ordered states with spherical building

motifs.

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Title:

Brittle-ductile transition under compression of glassy polymers: Role of chain

network

Jianning Liu

(Univ of Akron)

Xiaoxiao Li

(Univ of Akron)

Panpan Lin

(Univ of Akron)

Shiwang Cheng

(Oak Ridge National Laboratory)

Weiyu Wang

(Univ of Tennessee)

Jimmy Mays

(Oak Ridge National Laboratory)

Shi-Qing Wang*

(Univ of Akron)

Abstract:

It is of great fundamental and practical importance to understand what controls the

mechanical properties of polymeric glasses because of the diverse application of glassy

polymers in daily life. Polymeric glasses of high molecular weight including the most

brittle polystyrene (in tensile extension) are typically documented as ductile materials

in compression. The role of chain networking in glassy polymers of high molecular

weight have not been emphasized and well appreciated. It seems that theoretical studies

only need to develop a description of yielding and post-yield plastic deformation for

polymer glasses. But can yielding take place in compression if the molecular weight is

sufficiently reduced? In other words, can alpha processes be greatly accelerated during

external deformation in absence of chain networking? To address these questions, we

systematically explored the mechanical response over a range of temperature to uniaxial

compression at different rates of polystyrene with various molecular weights and

molecular weight distributions. Our preliminary results [1] show that PS of low

molecular weight is brittle in compression and chain networking is necessary (but not

sufficient) to ensure a ductile response. This work is supported, in part, by a NSF grant

(DMR-EAGER-1444859).

[1] Liu, J.; Lin, P.; Cheng, S.; Wang, W.; Mays, J. W.; Wang, S.-Q. Polystyrene

glasses under compression: Ductile and brittle responses. ACS Macro Letters 2015,

1072-1076.

13



Glass transitions and transport properties in hierarchically structured polymeric

ionic liquids

Tarak K Patra Junhong Yang, Yizi Cheng and David S. Simmons

The Department of Polymer Engineering, University of Akron

Polymeric ionic liquids (PILs) are poised to be a very promising material for higher density energy

storage device. The successful usage of PIL in energy applications requires molecular level

understating of their structure and dynamics. We conduct coarse-grained molecular dynamics

simulations for a wide range of temperature to investigate structural integrity and transport

properties of PILs with hierarchical molecular structure. One of the main objective of this study is

to identify suitable molecular architecture that has improved ion transport properties as well as

robust mechanical stability. Three levels of polymer architectures are considered - i) ion containing

co-polymers, where neutral monomers provide mechanical strength, and covalently bonded

ionomers guide the ion transport; ii) block copolymers where a neutral glassy block provides

mechanical integrity and an ion containing block facilitate free ion transport, and iii) ion containing

copolymers, which facilitate ion transport, in association with semi-telechelic polymers, which

provide mechanical integrity. We systematically analyze molecular level interactions and their

effects on ion transport. We demonstrate how do the mechanical stability and ion transport

properties change with the change in the molecular architecture. The work illustrates the

relationship between the mechanical and transport properties of PILs and with their side chain

length and spacing, χ parameters between blocks, free ion size, long range electrostatic interactions

in the system. The work provides very useful guidelines for designing energy storage polymeric

materials.

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Morphology and Mechanical Properties of Epoxy Networks Modified by Prereacted

Polyhedral Oligomeric Silsesquioxane and Silica Nanoparticles

Amit K. Sharma and Jeffrey S. Wiggins

Abstract:

Epoxy-amine networks were modified with well-defined inorganic building blocks- polyhedral

oligomeric silsesquioxanes (POSS) and silica nanoparticles. The self-assembly behavior between

POSS and silica nanoparticles was studied through controlled experiments to observe its

influence for generating nanostructured morphologies in epoxy networks cured by 4, 4’-diamino

diphenyl sulfone (44DDS). POSS molecules were incorporated in the organic-inorganic

networks as pendant chains within diglycidyl ether of bisphenol-A (DGEBA) monomer to

determine their self-assembly behavior with functional and non-functional silica nanoparticles

surfaces. The POSS-POSS and POSS-silica interactions are the main factors controlling the

network structure as these interactions mandate ultimate morphologies and the mechanical

properties of the developed organic-inorganic networks. As a result, because of these

interactions, the system becomes more homogenous and POSS and silica become better

dispersed during network formation. The developed hybrid networks were characterized via

SEM, TEM and DMA to study molecular and phase structure evolutions analysis and the

mechanical properties were investigated in compression mode to determine bulk modulus and

strain at the yield of these hybrid networks.

15



Recovery Timescales of Fracture-Healing Behavior of Thermoreversible Gels

Travis L. Thornell and Prof. Kendra A. Erk

School of Materials Engineering, Purdue University, 701 West Stadium Ave, West Lafayette, IN 47907

Acrylic thermoreversible physical gels were used as a model soft material system to investigate fracture-

healing behavior by shear rheometry. Gels were formed from triblock copolymers consisting of

poly(methyl methacrylate) endblocks and a poly(n-butyl acrylate) midblock dissolved in 2-ethyl hexanol.

By using shear start-up experiments, gels at various concentrations and temperatures were measured to

determine shear stress responses, and fracture was indicated by a decrease in shear stress (confirmed

with rheophysical flow visualization experiments). Fractured gels were allowed to recover in the

rheometer for set times and were tested again using the same shear start-up procedure to evaluate the

recovery kinetics of network strength. Relationships between the network recovery and the normalized

ratio of the resting times and characteristic relaxation times of the gels were determined. It was found

that resting times for fully healed networks needed to be 2 or 3 orders of magnitude greater than the

relaxation times. The extent of fracture was also investigated. Gels that were deformed to smaller total

strain magnitudes were suspected to have incomplete (or partial) fracture as results showed various

responses for given resting times. Viscous heating effects of the rheometer fixture were observed at

higher testing temperatures with longer deformation.

16



NGRPC 2016 Abstract

Title: Enhanced stability to high temperature steam by controlling crystallization of PAEKs

Authors: Dustin Veazey1,2

, Tim Hsu2, Enrique D. Gomez

1,3

1Department of Chemical Engineering, The Pennsylvania State University, University Park, PA

16802

2Polymics, Ltd., 2215 High Tech Road, State College, PA 16803

3Materials Research Institute, The Pennsylvania State University, University Park, PA 16802

Abstract:

The poly(aryl ether ketone) (PAEK) family of thermoplastic polymers is widely used in

oil and gas applications due to their excellent chemical resistance and good mechanical

properties at elevated temperatures. State-of-the-art technologies for enhanced oil and gas

extraction utilize aggressive chemicals and increasingly higher temperatures and pressures.

Polymeric materials used in down-hole applications must stand-up to high pressure, high

temperature (HPHT) conditions, while maintaining reasonable service life. Current commercially

available PAEKs struggle to meet the demands of current downhole environments, and will be

obsolete for next generation oil recovery technologies.

In this study, PEEK and various PEKKs were exposed to high pressure steam at

550°F(288°C). The effect on mechanical properties was measured by dynamic mechanical

analysis (DMA) in order to evaluate stability and potential for use under HPHT conditions.

Crystallinity and microstructure of exposed specimens were characterized using DSC and

WAXD. Exposure to high temperature steam for up to 72 hours causes an increase in

crystallinity for both PEEK and PEKK. The change is significantly more pronounced in PEKK

and correlates with embrittlement and reduction of mechanical strength. We demonstrate the

high temperature steam resistance of PEKK is improved through crosslinking the amorphous

phase, thereby inhibiting crystal growth during steam exposure. The crosslinked PEKK retains

mechanical properties at elevated temperatures and exhibits a stable microstructure. Such

crosslinking technologies are proposed to improve the HPHT resistance of PAEKs and give them

the potential to be used for current and future down-hole applications.

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Hydrophobically Crosslinked Supramolecular Hydrogels Stiffened by Surfactant

Author: Chao WangThe transient nature of supramolecular hydrogels enables re-arrangement of the

crosslinks to dissipate mechanical energy without catastrophic failure (rupture of

covalent bonds). This resistance to failure leads to many potential applications for

physically crosslinked hydrogels. However, these supramolecular hydrogels are

limited by their narrow range of the mechanical stiffness as various applications, such

as cell culture, are strongly dependent on the mechanical properties of the hydrogel.

Here we demonstrate a simple method to modulate the stiffness of a hydrophobically

crosslinked supramolecular hydrogel, based on a random copolymer of

N,N-dimethylacrylamide (DMA) and 2-(N-ethylperfluoro-octane sulfonamido) ethyl

methacrylate (FOSM), by addition of sodium dodecyl sulfate (SDS), an anionic

surfactant. In order to understand the origins of the changes in stiffness, we use small

angle neutron scattering (SANS) to examine the nanostructure of DMA/FOSM

hydrogel. The impact of the addition of SDS to the surrounding media of the hydrogel

is monitored with in situ SANS. Contrast matching of the components in the hydrogel

with H2O/D2O mixtures was used to probe the structural change of FOSM

hydrophobic crosslinks and the interconnecting DMA chain segments separately as

SDS diffuses into the hydrogel. The emergence of a shoulder at q~0.02 Å-1 provides

evidence for SDS-induced breakup of the hydrophobic FOSM crosslink in the

hydrogel. We attribute the stiffening of these hydrogels to the re-organization of the

DMA “loops” in the crosslinks to elastic strands during the crosslink breakup by SDS.

Examination of structural (via SANS) and mechanical (via rheology) changes provide

a consistent picture for the SDS induced re-organization of the physical crosslinks

and this insight can be used to design new supramolecular hydrogels with enhanced

mechanical stiffness.

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Supramolecular Elastomers. Particulate β-Sheet Nanocrystal- Reinforced

Synthetic Elastic Networks

Authors/Co-authors: Xuesong Yan, Joseph Scavuzzo, Yinghong Zhao, and Li Jia*

β-Sheet crystals in natural silks are particulate and less than 10 nm in size in all three

dimensions. In synthetic supramolecular analogues of natural silks, β-sheet crystals

have been found to be fibrous with the longest dimension exceeding 100 nm in the

hydrogen-bonding direction. This work demonstrates that particulate β-sheet crystals

can be achieved without any elaborate amino acid sequence but simply grafting

oligo(β-alanine) segments as pendent side groups on butyl rubber backbone. The

size control in the hydrogen-bonding direction is attributable to an entropic force that

opposes the driving force for the self-assembly. The nanocrystals, especially those of

trimeric β-alanine segments, display a remarkable ability to simultaneously provide

stiffness, extensibility, and strength to the synthetic elastic network and do so highly

efficiently at a low volume fraction of the material. The herein studied butyl

rubber-based thermoplastic elastomers containing no more than 3.6 vol % of β-sheet

nanocrystals are stiffer, stronger, and more extensible than

poly(styrene-b-isobutylene-b-styrene) reinforced by >33 vol % of polystyrene

domains. At higher temperatures that exceed the sevice temperature of styrenic

TPEs, the trimeric β-alanine-grafted butyl rubber displays 700% strain and 2 MPa

stress at failure. The high reinforcing efficacy of the β-sheet crystals is attributable to

two phenomena associated with their small sizes: a stick−slip mechanism for energy

dissipation and an auxiliary layer of polymer brush that contributes to increasing the

modulus.

19



Reversible thermal stiffening in polymer nanocomposites

Siyang Yang and Pinar Akcora

Department of Chemical Engineering and Materials Science

Stevens Institute of Technology

Maintaining dispersion and mechanical properties of polymer nanocomposites (PNCs) during

high temperature processing and applications holds a critical importance in manufacturing and

performance of polymeric products. In this work, a new reversible thermal-stiffening mechanism

in solvent-free PNCs of polymer-adsorbed nanoparticles is demonstrated without using

reversibly crosslinking or temperature responsive polymers. The shown stiffening behavior in

polymer nanocomposites can be used in applications for flexible electronics or mechanically

induced actuators responding to environmental changes like temperature or magnetic fields.

Miscible polymer blends with different glass transition temperatures (Tg) are known to create

confined interphases between glassy and mobile chains. We found that nanoparticles adsorbed

with a high-Tg polymer, poly(methyl methacrylate), and dispersed in a low-Tg matrix polymer,

poly(ethylene oxide), exhibit a liquid-to-solid transition at temperatures above Tg’s of both

polymers. The mechanical adaptivity of nanocomposites to temperature underlies the existence

of dynamically asymmetric bound layers on nanoparticles, and more importantly reveals their

impact on microscopic mechanical behavior of composites. The unusual reversible stiffening

behavior sets these materials apart from conventional polymer composites that soften upon

heating. To better understand the role of mobile bound polymer layer on the bulk properties of

composites, adsorption/desorption of other polymers such as PVAc and PMA on nanoparticles is

explored and will be discussed with their rheological results.

20



Internal Conduction from Interfacial Polarization in

Polypropylene/BaTiO3 Nanodielectrics

Guoqiang Zhang1, Daxuan Dong1, Longxiang Tang2, Saide Tang1, and Lei Zhu1,*

1. Department of Macromolecular Science and Engineering, Case Western

Reserve University, Cleveland, Ohio 44106, United States

2. Department of Polymer Science and Engineering, Hefei University of

Technology, Hefei, Anhui 230009, P. R. China

Contact e-mails: [email protected]

Polymer/inorganic particle nanocomposites (or nanodielectrics) have attracted pronounced

attention for electric energy storage applications, based on a hypothesis that polymer

nanodielectrics could combine the high permittivity of nanoparticles and the high electrical

breakdown strength of the polymer matrix for enhanced dielectric performance. Although higher

discharged energy densities have been reported for numerous polymer nanodielectrics, the

dielectric loss mechanisms, which are extremely important for eventual applications, are rarely

discussed. In this work, we intend to address the intrinsic dielectric loss mechanisms associated

with polymer nanodielectrics using a model system comprised of 70 nm BaTiO3 nanoparticles

(BT NPs) in an isotactic polypropylene (PP) matrix. The effect of space charge-induced

interfacial polarization on dielectric losses was investigated using bipolar and unipolar electric

displacement – electric field (D-E) hysteresis loops. Since the bipolar D-E loops always

exhibited more nonlinearity than the unipolar loops, the dielectric loss was attributed to the

internal AC conduction loss from the space charges (i.e., electrons and holes) in the BT NPs,

including boundary layer and bulk conductions. To mitigate the internal conduction along the

PP/BT interface, atomic layer deposition of a nanolayer (5 nm) of amorphous TiO2 was applied

to the BT NPs. Due to the higher resistivity, the coated amorphous TiO2 effectively reduced the

boundary layer conduction loss. Nonetheless, the bulk conduction loss in BT NPs still needed to

be reduced. This study suggests that more insulating high permittivity NPs are desired for

polymer nanodielectrics to enhanced dielectric performance.

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ral resentations echanical heological roperties of …...High Loading, Dispersion and Stabilization...

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