An Introduction to Electrospinning and Nanofibers by Kazutoshi Fujihara, Seeram Ramakrishna, and Teik-Cheng Lim

By

An Introduction to Electrospinning and Nanofibers
by Kazutoshi Fujihara, Seeram Ramakrishna, and Teik-Cheng Lim

Electrospinning

Contents

Foreword v
1. Introduction 1
1.1. Preface of Nanofibers 1
1.2. Nanotechnology and Nanofibers 3
1.3. Various Ways to Make Nanofibers 7
1.3.1. Drawing 10
1.3.2. Template Synthesis 12
1.3.3. Phase Separation 13
1.3.4. Self-Assembly 15
1.3.5. Electrospinning 15
1.4. Scope of This Book 18
2. Basics Relevant to Electrospinning 22
2.1. Material Classes 23
2.1.1. Polymers 23
2.1.1.1. Fundamental Classification of Polymer 24
2.1.1.2. Polymer Crystallinity 24
2.1.1.3. Polymer Molecular Weight 26
2.1.1.4. Glass Transition Temperature (Tg) 27
2.1.1.5. Synthetic Polymer 37
2.1.1.6. Natural Polymer 39
2.1.1.7. Copolymer and Polymer Blends 41
2.1.1.8. Electrospun Polymer Fiber 42
2.1.2. Composites 48
2.1.2.1 Composite Reinforcement 49
2.1.2.2 Polymer-Matrix Composite 50
2.1.3 Ceramics 51
2.1.3.1. Crystalline Structure 52
2.1.3.2. Amorphous Structure 53
2.1.3.3. Ceramic Biomaterials 54
2.1.3.4. Nanostructured Ceramics 55
2.1.3.5. Carbon 60
2.2. Solution Property 63
2.2.1. Surface Tension 63
2.2.1.1. Effect of Temperature on Surface Tensi on 65
2.2.1.2. Surface Tension of Solvent Mixtures 65
2.2.2. Polymer Solubility 66
2.2.2.1. Effect of Polymer Structure on Solubility 66
2.2.2.2. Gibbs Free Energy 67
2.2.3. Viscosity 69
2.2.3.1. Solvent Effect on Intrinsic Viscosity 71
2.2.3.2. Temperature on Intrinsic Viscosity 72
2.2.3.3. Viscometry 73
2.2.4. Volatility (Evaporation) of Solution 78
2.2.5. Conductivity of Solution 80
2.3. Electrostatics 81
2.3.1. Electric Field 82
2.3.2. Potential Difference and Electric Field Representations 83
2.3.3. Surface Charge of Insulator 84
2.3.4. Field Ionization 85
2.4. Conclusions 86
3. Electrospinning Process 90
3.1. Polymer Solution Parameters 91
3.1.1. Molecular Weight and Solution Viscosity 91
3.1.2. Surface Tension 96
3.1.3. Solution Conductivity 98
3.1.4. Dielectric Effect of Solvent 101
3.2. Processing Conditions 103
3.2.1. Voltage 103
3.2.2. Feedrate 106
3.2.3. Temperature 108
3.2.4. Effect of Collector 108
3.2.5. Diameter of Pipette Orifice / Needle Ill
3.2.6. Distance Between Tip and Collector 112
3.3. Ambient Parameters 113
3.3.1. Humidity 114
3.3.2. Type of Atmosphere 116
3.3.3. Pressure 116
3.4. Melt-Electrospinning 117
3.5. Creation of Different Nanofibers 117
3.5.1. Porous Nanofibers 118
3.5.2. Flattened or Ribbon-Like Fibers 122
3.5.3. Branched Fibers 125
3.5.4. Helical Fibers 126
3.5.5. Hollow Nanofibers 127
3.5.6. Fiber With Different Compositions 130
3.6. Uniformity and Productivity of Nanofiber Webs 130
3.6.1. Jet Stability 131
3.6.2. Multiple-Spinning Setup 132
3.7. Mixed Electrospun Fiber Mesh 133
3.8. Patterning 135
3.8.1. Cylinder Collector 135
3.8.2. A Knife Edge Disk 138
3.8.3. An Auxiliary Electrode/Electrical Field 139
3.8.4. Parallel Conducting Collector 142
3.9. Fiber Yarn and Textile 145
3.9.1. Hybrid Fiber Yarns 146
3.9.2. Electrospun Fiber Yarn 147
3.9.3. Twisted Fiber Yarn 148
3.10. Variations to Electrospinning 149
3.10.1. Scanning Tip Electrospinning Source 150
3.10.2. Nanofiber Interconnections Between Microscale Features.. 151
3.10.3. Mass Production Through Needleless Electrospinning 152
3.11. Conclusions 154
4. Modeling of the Electrospinning Process 155
4.0. Nomenclature 155
4.1. Introduction 157
4.2. Preliminaries 158
4.3. Assumptions 161
4.3.1. Jet Representation 161
4.3.2. Modeling Viscoelastic Behavior 162
4.3.3. Coordinate System 167
4.3.4. Liquid Incompressibility 168
4.4. Conservation Relations 168
4.4.1. Conservation of Mass 168
4.4.2. Conservation of Momentum 170
4.4.3. Conservation of Charge 172
4.5. Consideration of Forces 173
4.6. Instability 174
4.7. Results 179
4.8. Future Trends and Challenges 188
4.8.1. Jet Flow With Particles 189
4.8.2. Core-Shell Flow 189
4.8.3. Field-Assisted Flow 190
4.8.4. Multi-Jet Flow 190
4.8.5. Gas-Assisted Flow 190
4.9. Conclusions 191
5. Characterization 192
5.1. Morphology 193
5.1.1. Fiber Diameter 193
5.1.2. Pore Size and Porosity 199
5.1.3. Surface Contact Angle Measurement 206
5.1.4. Others 209
5.2. Molecular Structure 210
5.2.1. Crystalline Structure 210
5.2.2. Organic Group Detection 225
5.2.3. Others 229
5.3 Mechanical Property 234
5.3.1. Single Nanofiber 234
5.3.2. Nanofiber Yarn 240
5.3.3. Nanofiber Membrane 241
5.4. Conclusions 245
6. Functionalization of Polymer Nanofibers 247
6.1. Polymer Surface Modification 247
6.1.1. Introduction 247
6.1.2. Physical Coating or Blending 248
6.1.3. Graft Copolymerization 250
6.1.3.1. Radiation-Induced Graft Copolymerization 251
6.1.3.2. Plasma-Induced Graft Copolymerization 253
6.1.3.3. Oxidization-Induced Graft Copolymerization 255
6.1.4. Plasma Treatment and Chemical Vapor Deposition 256
6.1.5. Chemical Treatment 257
6.2. Functionalization of Nanofibers for Different Applications 261
6.2.1. Introduction 261
6.2.2. Functionalization of Nanofibers for Affinity Membrane
Application 261
6.2.3. Functionalization of Nanofiber for Tissue Engineering
Scaffold Application 266
6.2.4. Functionalization of Nanofibers for Sensor Application 269
6.2.5. Functionalization of Nanofiber for Protective Cloth
Application 271
6.2.6. Functionalization of Nanofibers for Other Applications 273
6.3. Conclusions 274
7. Potential Applications 275
7.1. Introduction 275
7.2. Affinity Membranes 279
7.3. Drug Release 285
7.4. Tissue Scaffolds 291
7.5. Wound Dressing 307
7.6. Filter Media 309
7.7. Chemical and Biological Protective Clothing 311
7.8. Energy and Electrical Application 320
7.9. Sensors 326
7.10. Composite Reinforcement 333
7.11. Conclusions 339
Appendix A Glossary of Terms 341
Appendix B Useful Websites on Electrospinning and Nanofibers 350
Bibliography 352
Index 381


Foreword
Even though research and development related to the electrospinning process and the electrospun nanofibers has increased in recent years, the availability of the corresponding literature is mainly confined to research journals. As a consequence, information on electrospinning process and electrospun nanofibers is comprehensible only for the highly specialized readers. The situation is further compounded as a result of differing approaches and perspectives from various interdisciplinary backgrounds. In spite of the numerous groups throughout the world investigating on electrospinning of nanofibers, the lack of introductory reading materials in this field is felt.

The appearance of this book is timely in view of this rapidly expanding field of science and technology. There exists a critical mass of information in this area for a book to be written. In order to attain a balanced perspective, this book was written by a group of researchers from various backgrounds – mechanical and chemical engineering, materials science, chemistry.

The contents page shows that this book covers a wide spectrum, which includes the basic materials used for manufacturing nanofibers, processing techniques and parameters, various characterization methods, various ways to produce different types of nanofibers, the surface modification & functionalization, theoretical understanding and modeling approaches, and finally the potential applications. The book is intended for the use of practicing engineers and scientists, as well as the students interested in electrospinning process and applications of the electrospun mats and nanofibers.

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