Polymer Microscopy

Third Edition

Polymer Microscopy

Third Edition

Linda C. Sawyer

David T. Grubb

Gregory F. Meyers

~ Springer

Linda C. SawyerCelanese Americas, ret.Palmyra, VA, USA

Gregory F. MeyersAnalytical SciencesDow Chemical CompanyMidland, MI, USA

David T. GrubbProfessorDepartment of Materials Science and EngineeringCornell UniversityIthaca, NY, USA

ISBN: 978-0-387-72627-4 e-ISBN: 978-0-387-72628-1DOl: 10.1007/978-0-387-72628-1

Library of Congress Control Number: 2007928814

© 1987, 1996, 2008 Linda C. Sawyer, David T. GrubbAll rights reserved. This work may not be translated or copied in whole or in part without the written permis­sion of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA),except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form ofinformation storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar meth­odology now known or hereafter developed is forbidden.The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are notidentified as such, is not to be taken as an expression of opinion as to whether or not they are subject to pro­prietary rights.

Printed on acid-free paper

987 6 5 4 3 2 1

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Preface to the Third Edition

The major objective of this text is to provide information on the microscopy techniquesand specimen preparation methods applicable to polymers. The aim is to provide enoughdetail for the methods described to be applied by the reader, while providing appropriatereferences for those who need more detail than can be provided in a single text.

We recognize that scientists from a wide range of backgrounds may be interested inpolymer microscopy. Some may be experienced in the field, and this text should providea reference source and a resource whenever a new material or a new problem comes totheir attention. The scientist, engineer or graduate student new to the field needs moreexplanation and help. The focus here is on the needs of the industrial scientist and thegraduate student. Some may need to know more about the intrinsic capabilities of micro­scopes of all types, so there is a description of basic imaging principles and of instruments,both classical and those more recently invented. Others may know all about microscopesand little about polymers, so there is a discussion of polymer structure and properties toput the microscopy into context. A brief section on processing of polymers has also beenadded.

As the text has been designed to cater to this wide range of backgrounds, some of thesemore introductory sections will not be for every reader. However, the organization ofchapter and section headings should lead the reader to the information needed, and anextensive index is provided for the same purpose.

The first edition of this book was published twenty years ago, in 1987, and a secondedition was published in 1996. There were many changes between those two editions, butthe advances in microscopy and polymers in the last decade have been even more signifi­cant, requiring major revision. We were pleased when Springer invited us to provide thisthird edition allowing us to bring "Polymer Microscopy" up to date once again. Thisedition follows the same basic principles as the first two, with significant editing of olderwork and inclusion of new material. The rapid development of Scanning Probe Micros­copy (SPM) and complete conversion to digital imaging has most affected the imagecapabilities used for polymers. Additionally, new polymer materials such as nanocom­posites have been developed that require the use of microscopy. Overall it has been anexciting decade for polymer microscopy and our goal is to provide a window to view thesenew technologies.

Chapter 1 provides a brief introduction to polymer materials, processes, morphologyand characterization. Chapter 2 is a concise review of the fundamentals of microscopy,where many important terms are defined. Chapter 3 reviews imaging theory for thereader who wants to understand the nature of image formation in the various types of

vi Preface to the Third Edition

microscopes, with particular reference to imaging polymers and how instrumental param­eters affect results. These chapters are summaries of large fields of science, to make thistext complete, and they contain many references to more specialized texts and reviews.

Chapters 4 and 5 contain the major thrust of the book. Chapter 4 covers specimenpreparation, organized by method with enough detail given to allow a reader to conductsuch preparations.* Many new methods have been added, especially those developed foruse with the SPM and those relating to improvements in cryo-TEM. The references arechosen to provide the best detail and support. Chapter 5 describes the application of thesemethods to the study of specific types of polymers. The organization is by the form ofthe material, as fibers, films, membranes, engineering resins and plastics, composites(including a new section on nanocomposites), emulsions, coatings and adhesives, and highperformance polymers. The emphasis in this chapter is on applications, particularly wheremore than one specimen preparation method or microscopy technique is used.

Chapter 6 is newly named for this edition, "Emerging techniques in polymer micros­copy." The change is to indicate that the chapter includes both techniques that have beenrecently developed and those which are not new but which have not yet been regularlyapplied to polymer materials. These techniques include optical, electron and scanningprobe microscopy techniques. In many of these fields the techniques are still developingvery rapidly and thus future improvement in practice and understanding is likely overthe coming years. Chapter 7 describes how the various microscopies and other analyticaltechniques for investigating polymer structure should be considered together as a systemfor problem solving.

The selection of the authors for this text came from a desire for a comprehensive reviewof polymer microscopy with emphasis on methods and techniques rather than on theresults obtained. The synergism provided by three authors with very different back­grounds is important. One author (LCS) has an industrial focus and a background inchemistry, while another author (DTG) is in an academic environment with a backgroundin polymer physics. A third author (GFM), added for this edition, is a chemist with anindustrial focus, and a specialist in SPM. The major contribution of David Grubb andGreg Meyers has been in Chapters 2, 3 and 6. Linda Sawyer has been responsible forChapters 1,4,5 and 7, with input from her coauthors.

ACKNOWLEDGEMENTS

Special thanks go to the former Microscopy group at Celanese Americas, formerly inSummit, New Jersey, whose efforts over the years provided many of the micrographsused in all three editions of this book. Madge Jamieson (deceased), Roman Brozynskiand Rong T. Chen and corporate support from Celanese Americas and from The DowChemical Company are also gratefully acknowledged.

Micrographs for the third edition are gratefully acknowledged from many colleagues,including: Olga Shaffer (Lehigh University, retired), Barbara Wood (DuPont), KarenWiney (University of Pennsylvania), David Martin (University of Michigan), Christian

*The specimen preparation methods used for microscopy of polymers involve the use ofmany hazardous and toxic chemicals as well as the use of instruments which can be radiationhazards. It is well beyond the scope of this text to provide the information required for theproper and safe handling of such chemicals and instruments. The researcher is strongly encouragedto obtain the required safety information from the chemicals and instrumental manufacturersbefore their use.

Prefaceto the Third Edition vii

Kiibel (Fraunhofer Institute), Ishi Talmon (Technion), David A. Zumbrunnen (ClemsonUniversity), G. Julius Vancso (University of Twente, the Netherlands), Javier GonzalezBenito (Universidad Carlos III de Madrid, Spain), Scot Gould (The Claremont Colleges),Gary Stevens (University of Surrey, UK), Inga Musselman (University of Texas, Dallas),Steven M. Kurtz (Drexel University), Vernon E. Robertson (JEOL, USA), Barbara Petti(Celgard LLC), Viatcheslav Freger (Ben-Gurion University of the Negev), Ron Ander­son (Materials Today), Anne Hiltner (Case Western Reserve University), Francis M.Mirabella (Lyondell Chemical), Eduardo Radovanovic (Universidade Estadual deMaringa'). Greg Meyers would also like to thank Georg Bar of the Dow ChemicalCompany who provided technical advice on SPM content. We would also like to thankthe many colleagues who supplied copies of their papers, advice and input on the contentof this text. Special thanks go to Prof. James P. Oberhauser, Dept. of Chemical Engineer­ing, University of Virginia, who enabled Linda Sawyer to have access to the UVA on-linelibrary and obtain the electronic files needed for this new edition.

Linda Sawyer thanks a very understanding colleague and husband, David Sawyer, who,as with the earlier editions, provided technical advice and support. David Grubb wouldlike to thank his wife, Sally, for her support over all the time spent on this project, andGreg Meyers would like to thank his wife, Debbie, for her support, patience, and under­standing for the time spent on the preparation of the book.

Linda C. SawyerLake Monticello, Virginia

David T. GrubbIthaca, New York

Gregory F. MeyersMidland, Michigan

May 2007

Contents

Color plates appear between pages 306 and 307.

Preface to the Third Edition v

1 Introduction to Polymer Morphology 1

1.1 POLYMER MATERIALS. . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . 11.1.1 Introduction............................................... 11.1.2 Definitions 2

1.2 POLYMER MORPHOLOGY 31.2.1 Amorphous Polymers 41.2.2 Semicrystalline Polymers 51.2.3 Liquid Crystalline Polymers 71.2.4 Multiphase Polymers 81.2.5 Composites 8

1.3 POLYMER PROCESSES 81.3.1 Fiber and Film Formation 91.3.2 Extrudates and Moldings 11

1.4 POLYMER CHARACTERIZATION 171.4.1 General Techniques 171.4.2 Microscopy Techniques 181.4.3 Specimen Preparation Methods 191.4.4 Applications of Microscopy to Polymers 201.4.5 Emerging Microscopy Techniques 21References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2 Fundamentals of Microscopy 27

2.1 INTRODUCTION 282.1.1 Lens-Imaging Microscopes 292.1.2 Scanning-Imaging Microscopes 30

2.2 OPTICAL MICROSCOPY 312.2.1 Introduction............................................... 312.2.2 Objective Lenses 322.2.3 Imaging Modes 322.2.4 Measurement of Refractive Index 342.2.5 Polarizing Microscopy 34

x Contents

2.3 SCANNING ELECTRON MICROSCOPY 352.3.1 Introduction ... .. . . . .. . .. . . . . .. . . . . . . . . . . . . ... . ... . .. . . . . . . 352.3.2 Imaging Signals 372.3.3 Electron Sources 392.3.4 SEM Types 412.3.5 SEM Optimization 41

2.4 TRANSMISSION ELECTRON MICROSCOPY 422.4.1 Conventional TEM 422.4.2 Scanning TEM 432.4.3 Electron Diffraction 442.4.4 High Resolution Electron Microscopy 45

2.5 SCANNING PROBE MICROSCOPY 452.5.1 Introduction... ... .. .......... . . . ... .. . . . . . . ... . . . .. . ... . . . 452.5.2 Atomic Force Microscopy ". . 472.5.3 SPM Probes 50

2.6 RADIATION SENSITIVE MATERIALS 512.6.1 SEM Operation 522.6.2 Low Dose TEM Operation 52

2.7 ANALYTICAL MICROSCOPY 532.7.1 X-ray Microanalysis 532.7.2 X-ray Analysis: SEM versus AEM 552.7.3 Elemental Mapping 55

2.8 QUANTITATIVE MICROSCOPY 562.8.1 Image Processing and Analysis 562.8.2 Three Dimen sional Reconstruction 572.8.3 Calibration ....... . ... . . .... . .. . . . ........... . .. . .. . . .. ... . 57

2.9 DYNAMIC MICROSCOPY 592.9.1 Mechanical Deformation Stages 592.9.2 Hot and Cold Stages 60References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

3 Image Formation in the Microscope 67

3.1 IMAGING WITH LENSES 683.1.1 Basic Optics 683.1.2 Diffraction 683.1.3 Image Formation 713.1.4 Resolution and Contrast 723.1.5 Phase Contrast and Lattice Imaging 763.1.6 D1umination Systems 783.1.7 Polarized Light 80

3.2 IMAGING BY SCANNING ELECTRON BEAM 853.2.1 Probe Formation 853.2.2 Probe-Specimen Interactions 883.2.3 Image Formation in the SEM 923.2.4 Low Voltage SEM 943.2.5 Variable Pressure SEM 96

3.3 IMAGING IN TH E ATOMIC FORCE MICROSCOPE 973.3.1 Microscope Components 973.3.2 Probe-Specimen Interaction 100

Contents Xl

3.3.3 Contact Mode AFM 1023.3.4 Intermittent Contact AFM 1053.3.5 Noncontact AFM 1123.3.6 Practical Considerations for AFM Imaging 1133.3.7 Artifacts in SPM Imaging 114

3.4 SPECIMEN DAMAGE IN THE MICROSCOPE 1183.4.1 Effect of Radiation on Polymers 1183.4.2 Radiation Doses and Specimen Heating . . . . . . . . . . . . . . . . 1203.4.3 Effects of Radiation Damage on the Image 1213.4.4 Noise Limited Resolution 123References ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

4 Specimen Preparation Methods 130

4.1 SIMPLE PREPARATION METHODS 1324.1.1 Optical Preparations 1324.1.2 SEM Preparations 1334.1.3 TEM Preparations 1334.1.4 SPM Preparations 140

4.2 POLISHING 1424.2.1 Limiting Artifacts 1424.2.2 Polishing Specimen Surfaces 143

4.3 MICROTOMY 1464.3.1 Peelback of FiberslFilms for SEM 1464.3.2 Microtomy for OM 1474.3.3 Microtomy for SEM 1504.3.4 Microtomy for TEM and SPM 1504.3.5 Cryomicrotomy for TEM and SPM 1544.3.6 Microtomy for SPM 1584.3.7 Limiting Artifacts in Microtomy 160

4.4 STAINING 1604.4.1 Introduction............................................... 1604.4.2 Osmium Tetroxide 1624.4.3 Ruthenium Tetroxide 1664.4.4 Chlorosulfonic Acid and Uranyl Acetate 1734.4.5 Phosphotungstic Acid 1754.4.6 Ebonite................................................... 1774.4.7 Silver Sulfide 1784.4.8 Mercuric Trifluoroacetate 1784.4.9 Iodine and Bromine 1794.4.10 Summary 179

4.5 ETCHING 1814.5.1 Solvent and Chemical Etching 1814.5.2 Acid Etching: Overview 1834.5.3 Permanganate Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1844.5.4 Plasma and Ion Etching 1884.5.5 Focused Ion Beam Etching 1944.5.6 Summary 195

4.6 REPLICATION 1964.6.1 Simple Replicas 1974.6.2 Replication for TEM 198

xii Contents

4.7 CONDUCTIVE COATINGS 2014.7.1 Coating Devices 2024.7.2 Coatings for TEM 2034.7.3 Coatings for SEM and STM 2034.7.4 Artifacts 2074.7.5 Gold Decoration 211

4.8 YIELDING AND FRACTURE . .. ...... .. .. . ... . . .. ... .. . .. .. . . . . 2124.8.1 Fractography 2124.8.2 Fracture: Standard Physical Testing 2134.8.3 Crazing 2174.8.4 In Situ Deformation 221

4.9 CRYOGENIC AND DRYING METHOD S 2264.9.1 Simple Freezing Methods 2264.9.2 Freeze Drying 2274.9.3 Critical Point Drying 2304.9.4 Freeze Fracture-Etching 2314.9.5 Cryomicroscopy 232References " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

5 Applications of Microscopy to Polymers 248

5.1 FIBERS 2505.1.1 Introduction. .. .. . . .. . .. ... . .. . . . ... ... . . ...... . . . . . . . . . . . . 2505.1.2 Textile Fibers 2515.1.3 Problem Solving Applications 2605.1.4 Industrial Fibers 2675.1.5 High Performance Fibers 270

5.2 FILMS AN D MEMBRANES 2765.2.1 Introduction.... . . . .. . .... .. . . .... . . ... ..... . . ....... . . . . . . 2765.2.2 Model Studies 2785.2.3 Industrial Films 2825.2.4 Flat Film Membranes 2945.2.5 Hollow Fiber Membranes 305

5.3 ENGINEERING RESINS AND PLASTICS 3085.3.1 Introduction . . . .. ...... . . . . . . ... . . . . . . . . . .. . ..... .. . . . . . . . . 3085.3.2 Process-Structure Considerations 3115.3.3 Single Phase Polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3165.3.4 Multiphase Polymers 3215.3.5 Failure or Competitive Analysis 349

5.4 COMPOSITES 3545.4.1 Introduction. . . .. . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 3545.4.2 Literature Review 3555.4.3 Composite Characterization 3575.4.4 Carbon and Graphite Fiber Composites 3655.4.5 Particle Filled Composites 3665.4.6 Nanocomposites 370

5.5 EMULSIO NS, COATINGS AND ADHESIVES 3805.5.1 Introduction . ........ .. . .. ...... . . . . . . .. . . . . . . . .. . .. . . . . . . . 3805.5.2 Emulsions and Latexes 3815.5.3 Particle Size Measurements 385

Contents xiii

5.5.4 Adhesives and Adhesion 3865.5.5 Wettability and Coatings 388

5.6 HIGH PERFORMANCE POLYMERS 3985.6.1 Introduction............................................... 3985.6.2 Microstructure of LCPs 4005.6.3 Molded Parts and Extrudates 4035.6.4 High Modulus Fibers 4095.6.5 Structure-Property Relations in LCPs 412References .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

6 Emerging Techniques in Polymer Microscopy 435

6.1 INTRODUCTION 4356.2 OPTICAL AND ELECTRON MICROSCOPY 436

6.2.1 Confocal Scanning Microscopy 4366.2.2 Optical Profilometry 4376.2.3 Birefringence Imaging 4386.2.4 Aberration Corrected Electron Microscopy. . . . . . . . . . . . . . . . . . . . 4386.2.5 Ion Microscopy 440

6.3 SCANNING PROBE MICROSCOPY 4416.3.1 Chemical Force Microscopy 4416.3.2 Harmonic Imaging 4436.3.3 Fast Scanning SPM 4446.3.4 Scanning Thermal Microscopy 4456.3.5 Near Field Scanning Optical Microscopy 4496.3.6 Automated SPM 449

6.4 THREE DIMENSIONAL IMAGING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4516.4.1 Introduction............................................... 4516.4.2 Physical Sectioning 4526.4.3 Optical Sectioning 4546.4.4 Tomography 455

6.5 ANALYTICAL IMAGING 4596.5.1 FTIR Microscopy 4596.5.2 Raman Microscopy 4606.5.3 Electron Energy Loss Microscopy 4616.5.4 X-ray Microscopy 4626.5.5 Imaging Surface Analysis 464References 468

7 Problem Solving Summary 478

7.1 WHERE TO START 4797.1.1 Problem Solving Protocol 4797.1.2 Polymer Structures 480

7.2 INSTRUMENTAL TECHNIQUES...... . . . . . . . 4807.2.1 Comparison of Techniques 4807.2.2 Optical Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4847.2.3 SEM Techniques 4857.2.4 TEM Techniques 4867.2.5 SPM Techniques 4877.2.6 Technique Selection 487

xiv Contents

7.3 INTERPRETATION .7.3.1 Artifacts .7.3.2 Summary .

7.4 SUPPORTING CHARACTERIZATIONS .7.4.1 X-ray Diffractiou .7.4.2 Thermal Analysis .7.4.3 Spectroscopy .7.4.4 Small Angle Scattering .7.4.5 Summary .References .

488489492492493495496499500501

Appendices

Appendix IAppendix IIAppendix IIIAppendix IV

Appendix V

Appendix VI

Appendix VII

Index

Abbreviation of Polymer Names .Acronyms of Techniques .Manmade Polymer Fibers .Common Commercial Polymers andTrade Names for Plastics, Films, andEngineering Resins .General Suppliers of MicroscopyAccessories .Suppliers of Optical and ElectronMicroscopes, Microanalysis Equipment,Image Analysis and Processing .Suppliers of Scanning Probe Microscopesand Related Supplies .

505

505506507

508

510

512

513

515

Chapter 1

Introduction to Polymer Morphology

1.1 POLYMER MATERIALS......... 11.1.1 Introduction 11.1.2 Definitions 2

1.2 POLYMER MORPHOLOGY 31.2.1 Amorphous polymers 41.2.2 Semicrystalline polymers 5

1.2.2.1 Crystallization underquiescent conditions .... 5

1.2.2.2 Crystallization underflow 6

1.2.3 Liquid crystalline polymers 71.2.4 Multiphase polymers 81.2.5 Composites 8

1.3 POLYMER PROCESSES.......... 81.3.1 Fiber and film formation 9

1.3.1.1 Fiber processes 91.3.1.2 Orientation methods 101.3.1.3 Film processes 11

1.3.2 Extrudates and moldings 111.3.2.1 Compounding 111.3.2.2 Extrusion processes 121.3.2.3 Injection molding

processes 121.3.2.4 Other molding

processes 141.3.2.5 Coating processes 151.3.2.6 Novel processes 15

1.4 POLYMERCHARACTERIZATION 171.4.1 General techniques 171.4.2 Microscopy techniques 181.4.3 Specimen preparation

methods 191.4.4 Applications of microscopy to

polymers 201.4.5 Emerging microscopy

techniques 21References 21

1.1 POLYMER MATERIALS

1.1.1 Introduction

Organic polymers are materials that are widelyused in many important emerging technologiesof the 21st century. Feedstocks for syntheticpolymers are petroleum, coal, and natural gas,which are sources of ethylene, methane, alkenes,and aromatics. Polymers are used in a wide rangeof everyday applications, such as in clothing,housing materials, medical applications, appli­ances, automotive and aerospace parts, and incommunication. Materials science, the study ofthe structure and properties of materials, isapplied to polymers in much the same way as itis to metals and ceramics: to understand therelationships among the manufacturing process,the structures produced, and the resulting physi­cal and mechanical properties. This chapter is anintroduction to polymer morphology, whichmust be understood in order to develop rela­tions between the structure and properties ofthese materials. An introduction by Young [1], arecent book on microstructure and engineeringapplications of plastics by Mills [2], and a bookby Elias [3] all provide a good starting point inany study of polymers. Subsequent sections andchapters of this book have many hundreds ofreferences cited as an aid to the interestedreader. The emphasis in this text is on the eluci­dation of polymer morphology by microscopytechniques. This first chapter provides a founda­tion for the chapters that follow.

Polymers have advantages over other types ofmaterials, such as metals and ceramics, becausetheir low processing costs, low weight, and prop­erties such as transparency and toughness form

2

unique combinations. Many polymers have usefulcharacteristics, such as tensile strength, modulus,elongation, and impact strength, which makethem more cost effective than metals and ceram­ics. Plastics and engineering resins are processedinto a wide range of fabricated forms, such asfibers,films,membranes and filters,moldings, andextrudates. Recently, new technologies haveemerged resulting in novel polymers with highlyoriented structures. These include polymers thatexhibit liquid crystallinity in the melt or in solu­tion, some of which can be processed into materi­als with ultrahigh performance characteristics.Applications of polymers are wide ranging andvaried and include the examples shown in Table1.1. A listing of the names and abbreviations ofsome common polymers is shown in Appendix Ifor reference. Appendix II is a list of acronymscommonly used for analytical techniques. Appen­dix III provides a listing of common fibers, andAppendix IV is a listing of common plastics anda few applications. Finally, general suppliers ofaccessories,microscopes, and x-raymicroanalysisequipment are found in Appendices V-VII.

1.1.2 Definitions

Polymers are macromolecules formed by joininga large number of small molecules, or mono-

TABLE 1.1. Polymer applications

Introduction to Polymer Morphology

mers, in a chain. These monomers, small repeat­ingunits, react chemically to form longmolecules.The repetition of monomer units can be linear,branched, or interconnected to form threedimensional networks. Homopolymers, com­posed of a single repeating monomer, and het­eropolymers, composed of several repeatingmonomers, are two broad forms of polymers.Copolymers are the most common form of het­eropolymers. They are often formed from asequence of two types of monomer unit. Alter­nating copolymers can be simple alternatingrepeats of two monomers, e.g., -A-B-A-B- A­B-A-B-, or random repeats of two monomers,e.g.,-A-A-A-B-B-A-B-B-A-A-B-, whereasblock copolymers include long sequences of onerepeat unit, e.g., -A-B-B-B-B-B-B-B-A-A­B-B-B-B-A-. There are several forms of blockcopolymers, including AB and ABA, where Aand B each stand for a sequence of severalhundred monomers. If monomer B is addedwhile A chains are still growing, the result is agraded block copolymer. Additionally, eachcomponent of block copolymers can be amor­phous or crystalline. Amorphous block copoly­mers generally form characteristic domainstructures, such as those in styrene-butadiene­styrene block copolymers. Crystalline blockcopolymers, such as polystyrene-poly(ethylene

Fibers

Films, packaging

Membranes

Engineering resins

Biomedical uses

Adhesives

Emulsions

Coatings

Elastomers

Polyethylene, polyester, nylon, acetate, polyacrylonitrile,polybenzobisthiazole, polypropylene, acrylic, aramid

Polyethylene, polyester, polypropylene, polycarbonate,polyimide, fluoropolymers, polyurethanes, poly(vinylchloride)

Cellulose acetate, polysulfone, polyamide, polypropyl­ene, polycarbonate, polyimide, polyacrylonitrile,fluoropolymers

Polyoxymethylene, polyester, nylon, polyethersulfone,poly(phenylene sulfide), acrylonitrile-butadiene-styrene,polystyrene

Acrylics, polyethylene, ultrahigh molecular weightpolyethylene (UHMWPE), polyester, silicone, nylon

Poly(vinyl acetate), epoxies, polyimides

Styrene-butadiene-styrene, poly(vinyl acetate)

Epoxies, polyimides, poly(vinyl alcohol)

Styrene-butadiene rubber, urethanes, polyisobutylene,ethylene-propylene rubber

PolymerMorphology 3

TABLE 1.2. Majorclasses of polymersCrystallizable Glassythermoplastics thermoplastics

oxide), typically form structures that are charac­teristic of the crystallizable component. Blockcopolymers that have the second componentgrafted onto the backbone chain are termedgraft copolymers. Graft copolymers of industrialsignificance, high impact polystyrene (HIPS)and acrylonitrile-butadiene-styrene (ABS),have rubber inclusions in a glassy matrix. Manycommon homopolymers can also be found asrepeat units in heteropolymers, such as polyeth­ylene, as in polyethylene-polypropylene copoly­mer. Modified polymers, copolymers, andpolymer blends can be tailored for specific enduses, which will be discussed.

There are three major polymer classes: ther­moplastics, thermosets, and rubbers or elasto­mers. Polymers that are typical of each of theseclasses are listed in Table 1.2. Thermoplastics areamong the most common polymers, and thesematerials are commonly termed "plastics".Linear or branched thermoplastics can be revers­ibly melted or can be dissolved in a suitablesolvent. In some cases, thermoplastics are cross­linked in processing to provide heat stability andlimit flow and melting during use. In thermosets,there is a three dimensional network structure, asingle highly connected molecule, which impartsrigidity and intractability. Thermosets are heatedto form rigid structures, but once set they do not

Polyacetal

Polyamide

Polycarbonate

Poly(ethyleneterephthalate)

Polyethylene

Polypropylene

Thermosets

Epoxy

Phenolic

Polyester(unsaturated)

Polystyrene

Poly(methyl methacrylate)

Poly(vinyl chloride)

Poly(vinyl acetate)

Elastomers

Polybutadiene

Ethylene-propylenecopolymers

Styrene-butadiene rubber

Ethylene-vinyl acetate

Styrene-butadiene copolymers

melt upon prolonged heating nor do they dis­solve in solvents. Thermosets generally haveonly short chains between crosslinks and exhibitglassy brittle behavior. Thermosets are used ashigh performance adhesives (e.g., epoxies).

Polymers with long flexible chains betweencrosslinks are rubbers and elastomers, which,like thermosets, cannot be melted. Elastomersare characterized by a three dimensional cross­linked network that has the well known prop­erty of being stretchable and springing backto its original form. Crosslinks are chemicalbonds between molecules. An example of acrosslinking reaction is the vulcanization ofrubber, where the sulfur molecules react withthe double bonded carbon atoms creating thestructure. Multiphase polymers, combinationsof thermoplastics and elastomers, take advan­tage of the ease of fabrication of thermoplasticsand the increased toughness of elastomers, pro­viding engineering resins with enhanced impactstrength.

The chemical composition of macromole­cules is important in determination of proper­ties. Variations in the stereochemistry, thespatial arrangement, also result in very differ­ent materials. Three forms of spatial arrange­ment are isotactic, syndiotactic, and atactic. Theisotactic (i) forms have pendant group place­ment on the same side of the chain, whereas insyndiotactic (s) polymers there is a regular,alternating placement of pendant groups withrespect to the chain. Atactic (a) polymers havedisordered sequences or a random arrange­ment of side groups. Isotactic polypropylene(iPP) crystallizes and has major uses, whereasatactic polypropylene (aPP) cannot crystallize,is sticky (has a low thermal transition) and findslittle application.

1.2 POLYMER MORPHOLOGY

In polymer science, the term morphology gen­erally refers to form and organization on a sizescale above the atomic arrangement but smallerthan the size and shape of the whole sample.The term structure refers to the local atomicand molecular details. The characterizationtechniques used to determine structure differ

4

somewhat from those used to determine mor­phology, although there is some overlap. Exam­ples of polymer morphology include the sizeand shape of fillers and additives, and the size,distribution, and association of the structuralunits within the macrostructure. However, as isprobably clear from the overlapping defini­tions, the terms "structure" and "morphology"are commonly used interchangeably. The char­acterization techniques are complementary toeach another, and both are needed to fullydetermine the morphology and microstructureand to develop structure-property-processrelationships.

X-ray, electron, and optical scattering tech­niques and a range of other analytical tools arecommonly applied to determine the structure ofpolymers. X-ray diffraction, for example, permitsthe determination of interatomic ordering andchain packing. The morphology of polymers isdetermined by a wide range of optical, electronand scanning probe microscopy techniques,which are the major subject of this text. Finally,there are many other analytical techniquesthat provide important information regardingpolymer structure, such as neutron scattering,infrared spectroscopy, thermal analysis, massspectroscopy, nuclear magnetic resonance, andso forth, which are beyond the scope of this textbut which are summarized in Chapter 7.

Polymers are considered to be either amor­phous or crystalline although they may not becompletely one or the other. Crystalline poly­mers are more correctly termed semicrystallineas their measured densities differ from thoseobtained for perfect materials. The degree ofcrystallinity, measured by x-ray scattering, alsoshows these polymers are less than completelycrystalline. There is no measurable order byx-ray scattering techniques and an absence ofcrystallographic reflections in noncrystalline oramorphous polymers. Characterization of semi­crystalline polymer morphology can require anunderstanding of the entire texture. This extendsfrom the interatomic structures and individualcrystallites to the macroscopic details and therelative arrangement of the crystallites in themacrostructure. The units of organization inpolymers are lamellae or crystals and spheru­lites [4]. Bulk polymers are composed of

Introduction to Polymer Morphology

lamellar crystals that are typically arranged asspherulites when cooled from the melt.

The general morphology of crystalline poly­mers is now well known and understood andwas described by Geil [5],Keller [6],Wunderlich[7], Grubb [8], Uhlmann and Kolbeck [9],Bassett [10, 11], and Seymour [12]. The work ofKeller and his group has been reviewed byBassett [13]. More recent edited books byBassett [14], Ciferri [15], and Ward [16, 17],among others, provide excellent updates oncurrent knowledge in the area of polymermorphology.

1.2.1 Amorphous Polymers

Amorphous polymers of commercial impor­tance include polymers that are glassy orrubbery at room temperature. Many amorphousthermoplastics, such as atactic polystyrene andpoly(methyl methacrylate), form brittle glasseswhen cooled from the melt. The glass transitiontemperature, Tg, or glass rubber transition, is thetemperature above which the polymer is rubberyand can be elongated and below which thepolymer behaves as a glass. Thermal analysis ofamorphous polymers shows only a glass transi­tion temperature, whereas crystalline polymersalso exhibit a crystalline melting temperature.

Commercially important glassy polymersinclude polymers that are crystallizable but thatmay form as amorphous materials. These non­crystalline polymers are formed by rapidcooling of a polymer from above the meltingtransition temperature. They yield by forming anecked zone where the molecules are highlyoriented and aligned in the draw direction.Other important polymers amorphous at roomtemperature include natural rubber (polyiso­prene) and other elastomers. These exhibit ahigh degree of elasticity, stretching consider­ably in the elastic region and then fracturingwith no plastic deformation.

Plastic deformation in glassy polymers and inrubber toughened polymers is due to crazingand shear banding. Crazing is the formation ofthin sheets perpendicular to the tensile stressdirection that contain fibrils and voids. Thefibrils and the molecular chains in them arealigned parallel to the tensile stress direction.

Polymer Morphology

Crazes scatter light and can be seen by eye aswhitened areas if there are many of them.Crazing is often enhanced by rubber inclusions,which impart increased toughness to thepolymer and reduce brittle fracture by initiat­ing or terminating crazes at the rubber particlesurface. Shear banding is a local deformation, atabout 45° to the stress direction, which resultsin a high degree of chain orientation. The mate­rial in the shear band is more highly orientedthan in the adjacent regions. The topic of yield­ing and fracture will be further explored (seeSection 4.8). Overall, the mechanical behaviorof amorphous polymers depends upon thechemical composition, the distribution of chainlengths, molecular orientation, branching, andcrosslinking.

1.2.2 Semicrystalline Polymers

Semicrystalline polymers exhibit a meltingtransition temperature (Tm ) , a glass transitiontemperature (Tg) , and crystalline order, asshown by x-ray and electron scattering. Thefraction of the crystalline material is deter­mined by x-ray diffraction, heat of fusion, anddensity measurements. Major structural units ofsemicrystalline polymers are the platelet-likecrystallites, or lamellae. The dominant featureof melt crystallized specimens is the spherulite.The formation of polymer crystals and thespherulitic morphology in bulk polymers hasbeen fully described by Keith and Padden [18],Ward [16, 19], Bassett [10, 11,20,21], and manyothers. Bassett [21] points out that a knowledgeof morphology is an essential part of the devel­opment of polymer materials and a completeunderstanding of their structure-property rela­tionships. Single crystals can be formed by pre­cipitation from dilute solution as shown later(see Fig. 4.1). These crystals can be found asfaceted platelets of regular shape for regularpolymers, but they have a less perfect shapewhen formed from polymers with a less perfectstructure. The molecular chains are approxi­mately normal to the basal plane of the lamel­lae, parallel to the short direction. Some chainsfold and re-enter the same crystal. In polyeth­ylene , the lamellae are on the order of severalmicrometers across and about 10-50pm thick,

5

independent of the length of the molecule. Bulkcrystallized spherulites can range from about 1to 100pm or larger. Small angle x-ray scattering(SAXS) and electron diffraction data have con­firmed the lamellar nature of single crystals inbulk material.

1.2.2.1 Crystallization UnderQuiescent Conditions

When a polymer is melted and then cooled itcan recrystallize, with process variables such astemperature, rate of cooling, pressure, and addi­tives affecting the nature of the structuresformed. Two types of microstructure observedfor semicrystalline bulk polymers are spheru­lites and row nucleated textures. Bulk crystal­lized material is composed of microscopic unitscalled spherulites, which are formed duringcrystallization under quiescent conditions. Thestructures exhibit radially symmetric growth ofthe lamellae from a central nucleus with themolecular chain direction perpendicular to thegrowth direction. The plates branch as theygrow. The molecular chains therefore run per­pendicular to the spherulite radius. The crystal­lite or lamellar thickness in the bulk polymerdepends upon the molecular weight of thepolymer, crystallization conditions, and thermaltreatment. The size and number of spherulitesis controlled by nucleation. Spherulites aresmaller and more numerous if there are moregrowth nuclei and larger if slow cooled or iso­thermally crystallized. In commercial processes,additives are commonly used to control nucle­ation density. When crystallizing during cooling,the radial growth rate of the spherulites is animportant factor in determining their size. Themorphology of isothermally crystallized poly­ethylene (PE) melts has revealed the nature ofthe lamellae [22] by a sectioning and stainingmethod for transmission electron microscopy(TEM) (see Fig. 4.15), which will be describedlater.

A schematic of the spherulite structure isshown in Fig. 1.1 [16]. The structure [16, 18,20,23] consists of radiating fibrils with amorphousmaterial, additives, and impurities between thefibrils and between individual spherulites.Although the shape of the growing spherulite

6

Defects in_-j'-__~..."fibrils

Singlecrysta lnucleus

Spherul iticchains folded atright angles tomain axis

Introduction to Polymer Morphology

FIGURE 1.1. Schematic of spher­ulite structure. (From Ward [19];used with permission.)

Amorphousinterspherulilicmater ial

Amorphousinterfibrillarmaterial

Spherulite

is round, as shown in a polarized light micro­graph (Fig. 1.2), spherulites generally impingeupon one another during cooling, resulting inpolyhedral shapes in the final product (Fig. 1.3).When thin melt quenched films or sections of abulk polymer are viewed in crossed polarizers,the spherulites appear bright because they areanisotropic and crystalline in nature. Isotropicmaterials exhibit the same properties in alldirections, whereas anisotropic rnaterials exhibita variation in properties with direction.

FIGURE1.2. Polarized light micrograph of this polyoxy­methylene film cooled from the melt shows recrystal­lization and formation of spherulites. The shape of thegrowing, birefringent spherulites is round.

Polarized light micrographs of a sectioned, bulkcrystallized nylon (Fig. 1.3) show the size rangeof spherulites obtained by bulk crystallization.A more complete discussion of polarizationoptics will be found later (see Section 2.2.5 andSection 3.1.7), but for this discussion it is clearthat the size of individual spherulites can bedetermined by analysis of polarized light micro­graphs. Average spherulite sizes are determinedby small angle light scattering techniques.

1.2.2.2 Crystallization Under Flow

When a bulk polymer is crystallized under con­ditions of flow,a row nucleated,or "shish kebab,"structure can be formed. Typically , the melt orsolution is subjected to a highly elongationalflow field at a temperature close to the meltingor dissolution temperature. A nonspherulitic,crystalline microstructure forms from elongatedcrystals aligned in the flow direction and con­taining partially extended chains . At high flowrates, these microfibers, some 20nm across,dominate the structure. At lower flow rates, thebackbones are overgrown by folded chainplatelets. This epitaxial growth on the surface ofthe extended chain produces folded chainlamellae oriented perpendicular to the strain orflow direction [23]. At still lower flow rates, thelarge lamellar overgrowths do not retain thisorientation. Dilute solutions of polymers stirredduring crystallization are known to form this

Polymer Morphology 7

FIGURE1.3. A thin section of bulk crystallized nylon, in polarized light , reveals a bright, birefringent and sphe ru­litic textur e. At high magn ification , a classic Maltese cross pattern is see n, with black crossed arms aligned in theposition of the crosse d polarizers (A); the sample was isothermally crystallized , and exhibits large spheru lites .Th e sample quenched during crystallization (B) yields large sphe rulites surrounded by smaller ones . (See co lorinsert.)

FIGURE 104. Schema tic of a shish kebab struc ture.(From Pennings [24]; used with permission.)

shish kebab structure where the shish is theelongated crystals in the row structure and thekebabs are the overgrown epitaxial plates, asshown in the schematic in Fig. 1.4 [24].

High modulus fibers and films are producedfrom extended chain crystals in both conven­tional polymers, notably PE , and in liquid crys­talline polymers (Lt.Ps). The topic of highmodulus organic fibers has been described andreviewed [15-17,25] providing inform ation ontheir preparation, structure, and properties.High modulus fibers are found in applicationssuch as fiber reinforced composites for aero­space, military, and sporting applications.Industrial uses are for belts, ropes , and tirecord s. Extended chain crystals can also formwhen polymers are crystallized very slowly nearthe melt ing temp erature, but they are weak andbrittl e.

1.2.3 Liquid Crystalline Polymers

Rigid and semirigid polymer chains form aniso­tropic structures in the melt or in solution, whichresult in high orientation in the solid state

8

without drawing. Liquid crystalline melts (ther­motropic) or solutions (lyotropic) are composedof sequences of monomers with long rigid mol­ecules. Aromatic polyamides and polyamide­hydrazides are examples of two polymers thatform liquid crystal solutions. Aromatic copoly­esters and polyazomethines form nematic liquidcrystalline melts at elevated temperature. Meltor solution spinning processing of anisotropicLCPs results in an extended chain structure in~he fiber or film. Heat treatment generallyImproves the orientation and the high modulusand tensile strength properties of thesematerials.

1.2.4 Multiphase Polymers

Many amorphous thermoplastics are brittlelimiting their range of applications. Tougheningwith rubber is well known to enhance fractureresistance and toughness. Many major chemicalindustries are based on toughened plastics, suchas ABS, HIPS, and ionomers [26-30]. Importantissues in the design of fracture resistant poly­mers are compatibility, deformation, toughen­ing mechanisms , and characterization. Particlesize distribution and adhesion to the matrixmust be determined by microscopy to developstructure-property-process relationships.

Rubber toughened polymers are usuallyeither copolymers or polymer blends. In randomcopolymers, a single rubber or matrix phasecan be modified by the addition of the secondcomponent. Graft and block copolymers havemodified properties due to the nature of therubber-matrix interface. In graft copolymers,grafting provides a strong bond between therubber and matrix in the branched structurewhere one monomer forms the backbone andthe other monomer forms the branch. Graftcopolymers are usually produced by dissolvingthe rubber in the plastic monomer and polym­erizing it to form the graft. Typical block copo­lymers are polystyrene-polybutadiene andpolyethylene-polypropylene. They have themonomers joined end-to-end along the mainchain , which results in a bonding of the twophases . New processes have resulted in novelpolymer blends that will be discussed in theprocess section of this chapter.

Introduction to Polymer Morphology

1.2.5 Composites

Polymer composites are engineering resins orplastics that contain particle and/or fibrousfillers. Specialty composites, such as those rein­forced with carbon or ceramic fibers, are usedin aerospace applications, and glass fiber rein­forced resins are used in automobiles and manyother applications requiring enhanced mechan­ical properties compared with the plastic. Com­posite properties depend upon the size, shape,agglomeration and distribution of the filler andits adhesion to the resin matrix. It is well knownthat long, well bonded fibers result in increasedstiffness and strength, whereas poor adhesionof the fibers can result in poor reinforcement~nd poorer properties. Fillers for polymersinclude glass beads, minerals such as talc clayand silica,and inorganic fillersused to strengthenelastomers. Small particles (carbon blacks orsilica) are added during manufacture to changecol?r or specificproperties, such as conductivity.Reinforcements that change mechanical prop­erties include long and short carbon and glassfibers. The toughness and abrasion resistanceimparted by fillers is very important in rubberapplications such as tire cords.

The theory, processes, and characterization ofshort fiber reinforced thermoplastics have beenreviewed by De and White [31], Friedrich et al.[32],Summerscales [33], in an introductory textby Hull and Clyne [34], and in a handbook byHarper [35]. Natural fibers and composites havebeen reviewed by Wallenberger and Weston[36].The introduction of new composite materi­als, called nanocomposites, has resulted in newmaterials that are being applied to variousindustrial applications. These materials have incommon the use of very fine, submicrometersized fillers, generally at a very low concentra­tion, which form novel materials with interest­ing morphology and properties.Nanocompositeshave been discussed in a range of texts includingtwo focused on polymer-clay nanocompositesby Pinnavaia and Beall [37] and Utracki [38].

1.3 POLYMER PROCESSES

The growing global market for plastics hasresulted in manufacturers focusing onperformance improvements and novel process-

Polymer Processes

ing to improve efficiencies and lower costs. Themajor point of this section is to emphasize thatthe structure and properties of polymers arebasically a function of their chemical composi­tion and the process used to make the product.The polymer manufacturing processes are notdiscussed here, but rather the focus is on theprocesses used to take neat polymers and formthem into useful products. There are many pro­cesses used to manufacture polymer materialsbut only the basic ones will be mentioned.Important commercial processes used to manu­facture polymer materials fall into three majorcategories: continuous (i.e., fiber spinning, extru­sion, pultrusion, and calendaring); semicontinu­ous (i.e., injection molding and blow molding);and batch (i.e., compression molding and ther­moforming) [39]. Another approach is to con­sider processes based on the form of the finalproduct (e.g., fibers, films, extrudates, moldings,etc.). Development of relationships between thechemical and physical structure and propertiesof the polymers requires an understanding ofthe specific process and its effect on the result­ing morphology. The objective of this section isto outline the nature of some basic processes,the important process variables, and the relationof those variables to the structure of the finalproduct. General references on the topic ofpolymer processes (e.g., [2, 16, 39-45]), equip-

9

ment manufacturers' Web sites, and the Societyof Plastics Engineers Web site and journalsshould be referred to for more specific detail.

1.3.1 Fiber and Film Formation

1.3.1.1 Fiber Processes

Polymer fibers are found in textile applications(Appendix III) for clothing and householditems, such as sheeting and upholstery, and alsofor industrial uses, such as cords, ropes, belts,and tire cords. Polymer fibers can be eithershort in length (staple fibers) or continuous,very long filaments. Fibers are produced by amelt or solution spinning process, as shown inthe schematic in Fig. 1.5 [46]. In either case, thepolymer melt or solution is extruded through aspinneret (or jet) to form the fiber, which coolsand crystallizes and is taken up on a bobbin andmay be further oriented by drawing on-line orby a post-treatment process resulting in hightensile strength and modulus. Requirements fortextile fibers are that the crystalline meltingtemperature must be above 200°C, so that thetextile fabric can be ironed, and yet below300°C, to permit conventional, melt spinningprocessing. Alternatively, the polymer is dis­solved in a solvent from which it can be spunby such processes as wet and dry spinning.

FIGURE 1.5. Schematic of fiber formationprocess for conventional and liquid crystal­line polymers. (From Calundann and Jaffe[46]; Celanese Americas, formerly HoechstCelanese; used with permission.)

Liquid Crystal

I I I II ! II

Nematic Structure

tII I I

I

Solutionor

Melt

Extrusion

1SolidState

Conventional (PET)

10

Polymers that can be melted within this rangeare typically melt spun and include polyesters,polypropylene, and nylon. Polymers that aresolution spun include some acetates and lyo­tropic LCPs. Schematic diagrams of the spin­ning apparatus are reviewed and shown, forexample, by Griskey [39] and have been wellknown for decades.

In tensile drawing, stress is applied, resultingin thinning and elongation of the crystal androtation of the molecules or bundles in thedraw direction; increasing the draw ratio isknown to increase the Young's modulus and thebreaking strength by improving the degree ofmolecular alignment or extension. The diame­ter of the microfibrillar texture is also affectedby the draw ratio with thinner microfibrils athigher draw ratios. The high speed spin-drawfiber process also yields fibers with high modulusand tensile strength when temperature, drawratio, and speed of the process are well con­trolled. Heat treatments are often used toimpart desired structures and properties in thefiber, and annealing of fiber forming thermo­plastics yields a highly crystalline morphology.Uniaxially oriented fibers have a high degree ofmolecular symmetry and high cohesive energyassociated with the high degree of crystallinity.Specific variables in the spinning processplay an important role in the final fiberproperties.

1.3.1.2 Orientation Methods

There are a variety of well known methods usedto orient materials, generally by use of tensilestress, as reviewed by Holliday and Ward [47],Ciferri and Ward [48], and Gedde [49]and morerecently by Ward [16, 50], Ciferri [15], andChung [44]. Orientation takes place during thespinning process, as the polymer is first extrudedthrough the spinneret, in the fiber skin and coreas they solidify, and by postspinning processes.Ductile thermoplastics can be cold drawn nearroom temperature, whereas thermoplastics thatare brittle at room temperature can only bedrawn at elevated temperatures. Thermosetsare oriented by drawing the precursor polymerprior to crosslinking, resulting in an irreversibleorientation. Rubbers can be reversibly elon-

Introduction to Polymer Morphology

gated at room temperature. The orientation inoriented rubbers is locked in place by cooling,whereas heating drawn thermoplastics causesrecovery.

Cold drawing is a solid transformationprocess, conducted near room temperature andbelow the melting transition temperature of thepolymer, if it is crystalline. The process yields ahigh degree of chain axis alignment by stretch­ing or drawing the polymer with major defor­mation in the neck region. Deformation of therandomly oriented spherulitic structure in ther­moplastics, such as in PE and nylon, results ina change from the stacked lamellae (ca. 20nmthick and l/.lm long) to a highly oriented micro­fibrillar structure (microfibrils lOnm wide andvery long) with the molecular chains orientedalong the draw direction, as shown in theschematic in Fig. 1.6 [51]. The molecules, linksbetween the adjacent crystal plates in thespherulites, also appear to orient and yet stillconnect the stacked plates in the final fibrillarstructure. Additionally, the drawing process

Am f

crysrct blocks

Fibril(bundle of microfibrilsl

Zone of micronecks

srcck of parallel lamellae

FIGURE 1.6. Schematic of cold drawing process withtransformation of the lamellar texture into a micro­fibrillar structure. (From Peterlin [51]; used withpermission.)

Polymer Processes

causes orientation in the noncrystalline amor­phous component of the polymer. The degreeof orientation of the crystalline component ischaracterized by wide angle x-ray scattering(WAXS) and birefringence. Clearly, the defor­mation process causes a major change in themicrostructure of the polymer resulting inimproved strength and tensile modulus.

1.3.1.3 Film Processes

Polymer films are used in many applicationsincluding packaging and electronic recordingand in membranes for separations applications.Films are formed by similar uniaxial or biaxialprocesses used for fibers that impart highstrength properties in either one or two direc­tions, respectively. Processes include filmextrusion, drawing, stretching, extrusion at highpressure through a die, and crystallization underflow. Extrusion is generally followed by stretch­ing to orient the structure and also by blownfilm manufacture (see Section 1.3.2). Deforma­tion processes that impart orientation to poly­mers can result in anisotropic mechanicalproperties. The increase in molecular alignmentcan result in increased stiffness and strength.The effects of orientation are dependent on thenature of the starting materials and on whetherthey are isotropic or anisotropic.

1.3.2 Extrudates and Moldings

Polymer morphology in extrudates and mold­ings is affected by process variables, such asmelt and mold temperature, pressure, shear,and elongational flow. Process variables affectthe morphology of the material thus affectingthe fabricated product performance andmechanical properties. Pressure increases, forinstance, can increase both the melting tem­perature and the glass transition temperatureof a polymer, with the result that the polymersolidifies more quickly. In a crystalline polymer,the nucleation density can increase, resulting ina decrease in spherulite size with increasedpressure in injection molding. In the specialcase of polymer blends, care must be taken tofully understand the effect of the process on thetwo or more polymers being used in the blendas even the size of the extruder or molding

11

machine can cause major changes in the localorientation and stresses in the part and thus themorphology and the final properties. Many ofthe references cited [39, 43, 52, 53] cover thistopic, but further references specific to polymerblends should be considered, for example, [26,28, 54] and others found in Chapter 5 in thevarious relevant application sections.

1.3.2.1 Compounding

Many of the fabricated plastic products manu­factured today include fillers and additivesto modify and/or reinforce the final productproperties. Fillers are blended with polymers tomodify physical properties, enhance tensilestrength or modulus or specific characteristics,such as wear resistance, flammability, electricalproperties, color, and so forth [34, 55], or toreduce the polymer level in expensive materi­als. Reinforcements modify strength andmodulus as the particles or fibers bear a frac­tion of the applied load. Compounding is theprocess of introducing fibers or particles into aresin prior to molding. Generally, the fillers oradditives are added to the molten polymer andthey are mixed together and extruded and cutinto pellets that can be used in other processessuch as molding. Process parameters, such asscrew design, melt temperature and pressure,relate to the structure in the final material. Highspeed and pressure are known to result in aglossy surface finish, and high melt temperatureis used to reduce viscosity and minimize fiberbreakage. Fillers such as titanium dioxide andclay are used in paints and adhesives as pig­ments or toughening agents. A book edited byWhite, Coran, and Moet [30] examines thecharacteristics and methods of preparingpolymer blends and compounds in batch andcontinuous mixing equipment.

Compounding of long fiber reinforced ther­moplastics (LFRTs) is very different from com­poundingshort fiber or particle filledcomposites.Long fibers enhance properties such as impactstrength and are finding great utility in a numberof applications in the automotive, industrial,and sports markets. Most of these products usePP or polyamide (PA), but poly(ethylene tere­phthalate) (PET) and other resins are also used.

12

Processes that are used for such compoundinginclude an extrusion process termed pultrusion.The formed shapes are structural, pipes andtubing or long pellets used for molding parts.Continuous fibers, such as glass or carbon fibers,are drawn through a heated die in this processforming highly oriented extrudates. In-line ordirect compounding of LFRTs can be done inwhich the compound with fibers and additivesis formed into extrudates and directly injectedinto the molding process to form a part. Mostof the pellets are used for injection molding butsome are also used for compression moldinggenerally for larger parts. The polymer viscosityand thermal properties are key factors in theprocess as are the standard process variables asnoted above.

1.3.2.2 Extrusion Processes

Fundamental factors of extrusion technologyhave been widely reviewed, for example, in aSociety of Plastics Engineers (SPE) Guideedited by Vlachopoulos and Wagner [56] and inbooks on polymer processing by Griskey [39],on polymer extrusion by Chung [44], and onpolymer blends by Utracki [29].As with all pro­cessing of polymers, extrusion involves thecontrolled melting and flow of the polymer andshaping of the material by forcing it through adie with an extruder. The goal is to form ahomogeneous melt at a uniform and high rateand is part of the extrusion, blow molding, andinjection molding process. Extruders are basi­cally helical screw pumps that convert solidpolymer particles to a melt delivered to a dieor a mold [39].These extruders are called singlescrew or twin screw devices depending on theactual number and type of screw used. Basi­cally, the process is similar to fiber processingin that the polymer in the form of pellets is fedinto a hopper and into the screw, which is drivenby a motor. Heat is generated both by theheaters and by the molten polymer itself. Theheated plastic is conveyed along the extruderuntil the pellets are melted and mixed wellthrough a series of sections that control themelt temperature, mixing, and pressure, andthus the final product. The choices of single,twin, and multiple screws and the screw designs

Introduction to Polymer Morphology

depend on the polymer used and the desiredproduct. For instance, twin screws provideincreased output and ability to handle materialscompared with single screws. Twin screw extru­sion is generally used for compounding poly­mers with fibers and fillers and also to fabricatenanocomposites. Process variables are used tocontrol the mixing, uniformity, and the rate ofproduction of extrudates.

Extruders are used in a wide range of pro­cesses to manufacture a range of products. Inthe simplest case, an extruded rod or pellet ofmaterial, with or without fillers, is produced andgenerally chopped to form pellets for variousother processes such as injection molding.Extruders are also used to manufacture fila­ments, rod and pipe, sheet, wire coatings, blownfilm, and cast film. Polymer properties thatinfluence the extrusion (and molding) processinclude molecular weight and molecular weightdistribution, melt rheology, thermal and mechan­ical stability, bulk density, compressibility, andmelt density. The thickness of the extrudates isimportant as is the extrusion speed, tempera­ture, and viscosity, all of which affect the overallstructure of the processed part. One of the keystructures affected by the process variables isthe size of the spherulites in the product, whichin turn affects properties such as the impactstrength, elongation, temperature resistance,among many others. Another structure of majorimportance is the skin-core morphology, whichresults from rapid cooling of the outside surfaceor skin of the extrudates versus the slowercooling of the central core region. This is a verysimple description of a very complex processthat should be well known to the engineers andscientists developing new materials and evaluat­ing process-structure-property relations.

1.3.2.3 Injection Molding Processes

Injection molding is widely used to produceplastic parts for a broad range of industries,notably electrical and electronic, automotive,appliances, medical, and so forth, because of itsflexibility to provide high rates of productionon parts with tight tolerance. In injectionmolding, a mix of polymer and fibers, fillers and/or additives is injected into a mold at elevated

Polymer Processes 13

temperature and pressure. These parts can beneat polymers or polymer blends, but they aremore commonly chopped fiber reinforced ther­moplastic composites. Molding is a semicontin­uous process during which polymer pellets arefed into the heated barrel, melted or thermallysoftened, injected or forced into the nozzle,sprue, runner, and gate on the way to the moldcavity. Once pressure is achieved, the mold iscooled and the part is ejected. Many of thefactors discussed for extrusion (in Section1.3.2.2) are similarly important for molding,such as melt temperature, mold temperature,injection rate, and of course material properties,such as viscosity (molecular weight), chemistry,and melt temperature. The thermal and shearhistory, which varies with location in the mold,also affects the molecular orientation and themorphology and thus the mechanical proper­ties of the molded article. Generally, the pelletsused for molding are pre dried as moistureaffects the viscosity and degradation of manypolymers. Gates are important because theypresent a high resistance to flow and they allowthe melt to reach the mold cavity quickly whileminimizing energy and pressure losses. Molddesign, especially for very fine parts, is criticalto the dimensional stability of the part and toshrinkage, warpage, and thermal and chemical

stability. Engineering details are found in thecited references and on the Web sites of machinemanufacturers.

Macroscopic product problems that canresult from poor control in injection moldinginclude, but are not limited to: voids and sinkholes on the surface generally due to poor moldfilling or low pressure, incomplete mold filling,weld lines and flow marks, warping or distortionof parts, high shrinkage, and so forth.

Microstructures that are typically observedin molded parts and extrudates include aniso­tropic textures. The higher orientation in extru­sion can result in highly oriented rods or strands,at high draw ratios and/or small diameters, orin structures with an oriented skin and a lessoriented central core in thicker strands. Thisskin-core texture is due to a combination oftemperature variations between the surfaceand the bulk and the flow field in both extrusionand molding processes. For instance, the flowfields in a molded part are shown schematicallyin Fig. 1.7 [46]. Extensional flow along the meltfront causes orientation. Solidification of thepolymer on the cold mold surface freezes in thisorientation. Flow between the solid layers isaffected by the temperature gradient in themold, and the resulting flow effects [57, 58]result in a rapidly cooled and well oriented skin

Injection Molding

Cross-Section

+~~--------')~

-....c::::: F~ozen Skin

Fllling_I=': -::~Stage =,::;;;=!~...=~;:=;;;....~~__..;::..",o~~ _

Molten Core

FiGURE 1.7. The pattern of the flowdirections in the injection moldingprocess is shown in the schematicdiagram. (From Calundann andJaffe [46]; Celanese Americas,formerly Hoechst Celanese; usedwith permission.)

P;:;:~~~.il~i)'jI I 0MeltFlow "Stagnant"

MeltPacking

14

structure and a slowly cooled, randomly ori­ented core. Extensional flow along the meltfront results in molecular orientation parallel tothe knit lines when two melt fronts meet. Theresulting knit, or weld line, is a region of weak­ness in the molded part, and weld line fracturesare commonly encountered. The local orienta­tion is quite important as tensile strength andimpact strength properties are known to behigher in the orientation direction.

Typically, in a semicrystalline polymer thereare three zones within the molded part: an ori­ented, nonspherulitic skin; a subsurface regionwith high shear orientation, or a transcrystallineregion; and a randomly oriented spheruliticcore. The thickness of the skin and shear zoneis known to be an inverse function of the meltand mold temperature with decreased tempera­tures resulting in increased layer thickness. Inthe skin, the lamellae are oriented parallel tothe injection direction and perpendicular to thesurface of the mold. Amorphous polymers alsoshow a thin surface oriented skin on injectionmolding. When amorphous polymers are heatedto the glass transition temperature and thenrelaxed, they exhibit shrinkage in the orien­tation direction and swelling in the otherdirections.

1.3.2.4 Other Molding Processes

There are other molding processes that will bementioned. Compression molding is a very oldmolding process generally used for thermoset­ting resins. Compression molding involves theintroduction of a resin and a curing or cross­linking agent into a mold followed by heatingand application of pressure to cause a reactionresulting in thermosetting the material in aspecific shape (e.g., [39, 52]). An overview ofthis topic including the underlying theory andphysics is found in a text on compressionmolding by Davis et al. [52]. Fillers and rein­forcements are used similar to those used ininjection molding. The morphology of the partsis complex due to the variation in thermal prop­erties and stress with position in the part. Theprocess is used for large parts that do notrequire good tolerance compared with injectionmolding.

Introduction to Polymer Morphology

Blow molding is a very common process thatis used to produce hollow objects. Products asdifferent as food and beverage products, fueltanks, cylinders, and blown film are formedby three different processes: extrusion blowmolding, injection blow molding, and stretchblow molding. In extrusion blow molding ahollow tube of molten or thermally softenedpolymer, termed a parison, is extruded into asplit cavity mold and crimped at one end. Com­pressed air is blown into the parison to fit themold shape, causing the polymer to solidify. Ininjection blow molding, molten or softenedpolymer is injected into a heated mold cavityaround a core pin and then the mold is openedand moved using the core pin where it is blownopen and then ejected. Stretch blow moldingcan be by either extrusion or injection moldingand results in a biaxially oriented product.Variables that are important to the morphologyinclude thermal properties and rheology of thepolymer and the transfer of heat through thepart during the process. Multilayer blow moldingis also increasing in demand due to potentiallyimproved barrier properties. These processesare quite complex and this brief section onlyintroduces the topic, which is described else­where (e.g., [39, 43, 53, 59]).

Thermoforming is another process used formaking polymer products, such as automotivepanels, underhood and fuel tank applications,chemical tanks, and packaging materials for themedical and electronics industries. A sheetformed by another process, such as extrusion, ispreheated and then placed in a heated moldunder pressure to form it into a part. Variationson the method include simple heating andstretching, pressure forming, contact forming,and so forth [60]. The thermoforming process isviewed as an alternative to blow molding, and itcan also handle multilayered sheets such as thoseneeded for plastic fuel tanks. Whereas an entiretank is formed by blow molding, thermoformingcan involve making two halves of a tank andwelding them together after all components areplaced in them. As with most other processes, thefinal product properties are a function of thematerial's thermal, rheological, and chemicalproperties, and these are affected by the processvariables, which, in turn, affect the morphology

Polymer Processes

of the part. One of the advantages of thermo­forming is the production of high gloss surfaceswithout painting, key to some automotive appli­cations as a metal replacement. Once again, thisis a brief summary of a very complex engineeringprocess that the polymer microscopist needs tobe aware of in understanding process-structure­property relationships; for more details on theprocess, see the many Web sites and books onprocessing and properties (e.g., [16,43,60]).

Reaction injection molding (RIM) is gener­ally used for thermoset polyurethane, nylon,polyesters, and epoxies [39].This process gener­ally uses two metered reactive streams thatcombine and mix and then are injected into themold. In the case of urethanes, one stream con­tains a polyether backbone, a catalyst, and acrosslinking agent, and the other has an isocya­nate. The use of a blowing agent expands thematerial after mixing to fill the mold.

1.3.2.5 Coating Processes

There is a wide variety of polymer coatings andof processes to apply them to other polymers,metals, electronic devices, and for many appli­cations in the aircraft, chemical and petroleum,food, textiles, and transport industries [43, 61,62]. For example, polymer based coatings areused to protect steel from corrosion and extrud­ers used in food and medical applications fromwear. Adhesion is important if good protectionis sought. A text by Grainger and Blunt [61]describes the many methods used for formationof surface coatings and surface modification,generally used to delay degradation and prolongthe life of engineering components. The mecha­nisms of wear and corrosion must be under­stood if the coating is to provide protection.Coatings are applied by spin casting, thermalspray, electrodeposition, physical and chemicalvapor deposition, laser surfacing, and variouspowder methods.

Licari [62] in his book on materials and pro­cesses for electronics applications describes theproper application of coating materials for theprotection of electronics from environmentalfactors such as humidity, temperature, and highspace vacuum for military and commercialapplications. The chemistry and properties of a

15

broad range of polymer coatings are discussed,including acrylics, polyesters, polystyrenes,epoxies, polyurethanes, silicones, polyimides,benzocyclobutene, fluorocarbons, polyamides,phenolics, and polysulfides. Processes discussedare spray coating, aerosol spray, electrostaticspray, dip coatings, fluidized bed coating,electrocoating, vapor deposition, spin coating,extrusion coating, and many others. Clearly, thevarious coating methods are affected by thepolymer chemistry, thermal stability, rheology,and other factors that affect the coating thick­ness, adhesion, and degradation. The polymermorphology is a direct result of the chemistryand properties of the polymer and the impactof the specific process used for its application.

1.3.2.6 Novel Processes

Several processes will be discussed in thissection that are not as commonly applied topolymers but have found niches for new appli­cations. The first to be discussed is the forma­tion of novel composites by hot compaction offibers, developed by Ward and his group atLeeds (e.g., [63-65]). In this process, highly ori­ented fibers, such as melt and gel spun PE, PET,and LCP fibers are compacted until selectivesurface melting of some of the fibers permitsthe formation of a fiber composite with highstrength and stiffness [63]. Potential applica­tions of these materials include automotiveindustry, sports protection equipment, andmany others [64] requiring exceptional mechan­ical properties. Investigation of the variousprocess parameters showed that the time spentat the compaction temperature, termed thedwell time [65], was critical to formation of thecomposite. Molecular weight measurementsshowed that hydrolytic degradation occurredrapidly at the temperatures required for suc­cessful compaction, leading to embrittlement ofthe materials with increasing dwell time; a dwelltime of 2 min was found to be optimum to haveenough melted material to bind the structuretogether while resulting in only a small decreasein molecular weight. These studies includedevaluation of mechanical properties and mor­phology that resulted from variations in theprocess variables and the polymer, such as the

16

use of high molecular weight materials, whichresulted in high impact performance of the hotcompacted sheets.

Layer multiplying coextrusion is a processthat has been used to fabricate one dimensionalpolymer blends by forced assembly of two poly­mers into many alternating thin layers (e.g.,[66]) even to the level of nanolayer films con­sisting of thousands of continuous layers of twopolymers with layer thickness less than lOnm.Multilayer films have potentially improvedimpact strength and may also have enhancedpermeability useful for many industrial applica­tions. A schematic of the process used formicrolayer and nanolayer coextrusion in Fig.1.8 [66] shows that the viscoelastic nature ofpolymer melts is to repeatedly split. The processpermits two immiscible polymers to come intointimate contact, and the localized mixingcreates an "interphase" region, key to the prop­erties of polymer blends [28]. A critical processvariable, in the case of an amorphous polyesterand polystyrene, is the extruder temperature,which was adjusted to ensure that the viscosi­ties matched when the melts were combined inthe feed block. Once the melt exited the assem­bly, it was spread in a film die to further reducethe layer thickness and rapidly quenched on achill roll equipped with an air knife to freezethe melt morphology. The number of layers isdependent on the number of die elements, andthe film thickness ranged from more than 10/lmto a few nanometers [66]. The film propertieswere clearly a result of the morphology frozenin by the process and affected by the processvariables used. An example of a film formedusing this process will be described further inSection 5.2 (see Fig. 5.38).

Introduction to Polymer Morphology

The development of chaotic advection, initi­ated more than two decades ago by Aref andreviewed by him more recently [67], has led toits application and development for materialsprocessing of polymer blends and clay nano­composites by Zumbrunnen and his group atClemson University [68-72]. This process hasthe exciting result of providing significantimprovements to the impact properties ofblends by addition of low volumes of the secondphase. In one case [68], a polystyrene matrixwas improved by the addition of only 9% byvolume of low density PE (LDPE). The poly­mers were combined in the molten state withina cylindrical cavity where a quiescent, threedimensional chaotic mixing process resulted inthe formation of stretched and folded minorphase domains that were interconnected andstable upon solidification. The unique micro­structures were due to the process used anddiffered from the normally observed finedomain textures that generally result whenusing low volumes of a second phase polymer.The process has also been used in continuousflow to form extruded films with many layers. Abatch process study of polystyrene and LDPEwas used as a model binary system so thatthicker layers could be formed for evaluation[69]. Figure 1.9 [71] is a schematic of the con­tinuous chaotic advection blender (CCAB). Inthis study, the unique CCAB was used to inves­tigate the influence of the morphology formedon tensile and impact toughness properties ofblends of polypropylene (PP) with LDPE.Process control of the melt flow, and the stirrods, as well as the specific machinery design isimportant to obtaining the unique morphologythat is responsible for the unexpected property

Polymer A

Polymer B151 Die Element 2nd Die Element

FiGURE 1.8. Schematic of layer multiplying coextrusion used for forced assembly of polymer nanolayersshows that two die elements multiply the number of layers from 2 to 8. (From Liu et al. [66], © (2004)American Chemical Society; used with permission.) (See color insert.)

Polymer Characterization

Progressive Morphology TaperedCircularStirDeve lopment Rods in Oval Barrel

~ A,-_~L.1.""'-'-rT-'~

Extrusions

~-Metering

Pump

Polymer B

............................................. .Process Control

Computer!+-------~ ..

17

FIGURE 1.9. Schematic representation of the continuous chaotic advection blender. (From Zumbrunnenet a!. [71], © (2005) Elsevier; used with permission.)

profiles. Further study currently under wayinvolves the flow of the melt from this processinto molds to maintain and control the mor­phology in molded parts [71].Film formed usingthis process is described in Section 5.2 and anexample shown in Fig. 5.39; an example ofa nanocomposite formed by this process isdescribed in Section 5.4 (see Fig. 5.109).

1.4 POLYMERCHARACTERIZATION

With the invention of scanning probe micro­scopes more than 25 years ago, the entire fieldof materials exploded into the realm of thenanoworld. The ease of imaging atoms and mol­ecules has opened up the characterization ofmaterials including polymers. The microscopeshave changed and enabled materials to changeas well, composites now include nanocompos­ites, and so on. Thus, the characterizationof materials has changed dramatically inthe past decade. Advances in many other

microscopy and analytical techniques hasalso resulted in additional information beingavailable about materials. The need for com­plementary techniques to fully understandmaterials continues to be required for fullunderstanding of structure-property-processrelationships.

1.4.1 General Techniques

A very wide range of analytical techniques areused to characterize polymer materials (e.g., seereferences on polymer physics [49], thermalanalysis[73,74],light microscopy [75,76],Raman[77, 78], x-ray scattering [79], various spectros­copies [80, 81], and a wide range of microscopytechniques [82]). A text on polymer blends alsodescribes many polymer characterization tech­niques [83].Texts on microscopy with a focus onbiological materials are often useful for thepolymer microscopist (e.g., [84,85]) as the mate­rials have in common a tendency to be soft, torequire contrast enhancement, and to sufferfrom radiation damage in electron beam in­struments. The primary characterization of an

18

organic material must be chemical. Elementalanalysis by wet chemistry or spectroscopy maybe useful in a few cases, for example to deter­mine the degree of chlorination in chlorinatedPE, but most chemical analysis is at the level ofthe functional group. Ultraviolet/visible spec­troscopy and mass spectroscopy (MS) of frag­ment s broken from the polymer chain are oftenused. Even more common spectroscopies areinfrared (IR) absorption, Raman, and nuclearmagnetic resonance (NMR), which is veryimportant. All of these can distinguish specificchemical groups in a complex system. Ramanmay be used on small particles and inclusionsmuch more easily than IR, but IR and in par­ticular Fourier transform IR (FTIR) has advan­tages of sensitivity and precision. Nuclearmagnetic resonance also gives local informa­tion, on a very fine scale, about the environmentof the atoms investigated.

Once the chemistry of the molecule is known,the next important characteristic is the molecu­lar weight distribution (unless the material is athermoset or elastomer with infinite molecularweight). The molecular weight distribution isdetermined by a range of solution methods ofphysical chemistry, viscometry, osmometry,light scattering, and size exclusion chromatog­raphy. Chemical and physical characterizationmethods overlap in the polymer field, for NMRof solid samples can determine the mobility ofatoms in various regions and the orientation ofmolecules. IR and Raman are also sensitive toorientation and crystallinity of the sample.

There are two further general types of physi­cal characterization. They involve either scatter­ing of light, neutrons, or x-rays or the formationof images of the polymer by microscopy, thesubject of this text. Electron diffraction logicallybelongs in the firstgroup but is always performedin an electron microscope, so it is associated with

Introduction to Polymer Morphology

microscopy. This technique shares with micro­scopy the ability to determine the structure of alocal region, whereas other scattering methodsdetermine the average structure in a large samplevolume. The impact of electron crystallographyon the study of polymer materi als has beenreviewed by Voigt-Martin [86, 87].

The past decade has seen the emergence ofanalytical imaging, which is imaging using thesignals from various analytical instruments ,such as FTIR and Raman microscopy, x-raymicroscopy, and imaging by surface analysisusing secondary ion mass spectrometry (SIMS)and x-ray photon spectroscopy (XPS).

1.4.2 Microscopy Techniques

Microscopy is the study of the fine structureand morphology of objects with the use of amicroscope. Resolution and contrast are keyparameters in microscopy studies, which will bediscussed further. The specimen and the prepa­ration method also affect the actual informa­tion obtained as the contrast must permitstructures to be distinguished. Optical brightfield imaging of multiphase polymers, forinstance, has the potential of resolving detailsless than 1pm across; however, if thepolymers are both transparent, they cannot bedistinguished due to a lack of contrast. Thereare variations among microscopes in availableresolution, magnification , contrast mechanisms,and the depth of focus and depth of field.Optical microscopes produce images with asmall depth of focus, whereas scanning electronmicroscopes (SEMs) have both a large depth offocus and large depth of field.

There is a wide range of microscopy instru­ments available that can resolve details rangingfrom the millimeter to the subnanometerscale (Table 1.3). The size and distribution of

TABLE 1.3. Characterization techniques: Sizeranges

Wide angle x-ray scatte ring (WAXS)Small angle x-ray scattering (SAXS)Transmission electro n microscopy (TEM)Scanning probe microscopy (SPM, AFM , STM, etc.)Scanning electron microscopy (SEM)Optical microscop y (OM)Light scattering (LS)

0.01-1.5nm1.5-100nm0.2nm-O.2mm0.2nrn-Il.Zmm4 nm--4mm200nm-2oopm2oo nm~200pm