Applications of Polymer Nanofibers

Anthony L. Andrady, PhD, is Adjunct Professor of Chemical and Biomolecular Engineering at North Carolina State University. He is a Fellow of the Royal Society of Chemistry and the National College of Rubber Technology in London, England. He holds 7 US patents pertaining to electrospun polymer nanofibers and in 2007, he authored “Science and Technology of Polymer Nanofibers.” His present research interests include the origins of short polymer fibers (both micro- and nanoscale) in the environment. Dr. Andrady is the author of over 150 research publications in scientific journals and has edited or authored 5 books in the general area of polymers. Saad A. Khan, PhD, is INVISTA Professor and Director of the Graduate Program in the Department of Chemical and Biomolecular Engineering at North Carolina State University. He is a Fellow of the Society of Rheology and has research interests in soft solids that includes functional nonwovens, gels, suspensions, nano- and micro-fibers, and aerogels. Dr. Khan holds 16 patents, has published over 230 scholarly papers, and has edited a book in the area of foams.

Preface xiii

1 Electrospinning Parameters and Resulting Nanofiber Characteristics: Theoretical to Practical Considerations 1
Christina Tang, Shani L. Levit, Kathleen F. Swana, Breland T. Thornton, Jessica L. Barlow, and Arzan C. Dotivala

1.1 Electrospinning Overview 1

1.2 Effect of Process Parameters 2

1.2.1 Theoretical Analysis 2

1.2.2 Experimental Results 5

1.3 Effect of Setup Parameters 6

1.4 Effect of Solution Parameters 11

1.4.1 Polymer Solution Properties (Molecular Weight, Concentration, Viscosity, and Elasticity) 11

1.4.2 Solvent Selection 14

1.4.3 Additivities to Tune Solution Properties 16

1.4.3.1 Surface Tension 16

1.4.3.2 Conductivity 16

1.5 Electrospinnable Systems 17

1.5.1 Nonpolymer Electrospinning 18

1.6 Advanced Fiber Characteristics 20

1.6.1 Ribbons, Wrinkles, Branching, and Netting 20

1.6.2 Porous Fibers 21

1.6.3 Core–Shell Fibers 24

1.6.3.1 Coaxial Electrospinning 24

1.6.3.2 Emulsion Electrospinning 25

1.7 Process Scalability 26

1.7.1 Melt Electrospinning 26

1.7.2 Needleless or “Free-Surface” Electrospinning 29

1.7.3 Alternative Fiber Production Methods 30

References 32

2 Textile Applications of Nanofibers 41
Jiadeng Zhu, Yeqian Ge, and Xiangwu Zhang

2.1 Introduction of Nanofibers in Textile Applications 41

2.2 Fabrication of Nanofiber Yarns 42

2.2.1 Electrospinning 42

2.2.2 Bicomponent Spinning 43

2.2.3 Melt Blowing 44

2.2.4 Flash Spinning 44

2.2.5 Centrifugal Spinning 45

2.2.6 Formation of Nanofiber Yarns 45

2.3 Structure and Properties of Nanofiber Yarns 47

2.4 Fabrication of Nanofiber Fabrics 52

2.4.1 Nanofibrous Nonwoven Fabrics 52

2.4.2 Nanofibrous Woven Fabrics 54

2.5 Characteristics and Specialized Applications of Nanofiber Fabrics 57

2.5.1 Protective Clothing 57

2.5.2 Filter Fabrics 58

2.5.3 Wearable Devices 59

2.5.4 Functional Fabrics 60

2.5.5 Biomedical Textiles 61

2.6 Summary and Future Trends 61

References 62

3 Nanofiber Mats as High-Efficiency Filters 68
Howard J. Walls and David S. Ensor

3.1 Introduction 68

3.1.1 Background 68

3.1.2 Filtration Overview 69

3.1.3 Available Information 70

3.1.4 Scope of This Chapter 70

3.2 Filters Made with Nanofibers 72

3.2.1 Consequences of Reducing Fiber Size 72

3.2.2 Slip Flow 73

3.2.3 Pressure Drop 74

3.2.4 Particle Collection Mechanisms 76

3.2.5 Evaluation 81

3.2.6 Nanofiber Media Modeling 82

3.3 Filtration Developments 82

3.3.1 Media Scale 83

3.3.1.1 Support Substrates 83

3.3.1.2 Mixed Bead-Fiber Systems 85

3.3.1.3 Unsupported Nanofiber Membranes 85

3.3.1.4 Multilayer Mats 86

3.3.1.5 Intermingled Nanofiber Mats 87

3.3.1.6 Mesh Substrates 87

3.3.1.7 Mat Morphological Modifications 87

3.3.2 Fiber Scale 88

3.3.2.1 Functional Fibers 88

3.3.2.2 Coated Fibers 88

3.3.2.3 Combining Nanofibers and Nanoparticles for Dual Function 89

3.3.2.4 Core Shell Fibers 89

3.3.2.5 Electrostatics 90

3.4 Outlook 90

Acknowledgments 92

References 92

4 Nanofiber-Based Chemical Sensors 100
Anthony L. Andrády

4.1 Introduction 100

4.2 General Features of Sensors 104

4.3 Nanofibers as a Sensor Material 105

4.3.1 Nanofiber vs. Thin-Film Geometry 106

4.4 Approaches to Nanofiber Sensor Design 109

4.5 Gravimetric Nanofiber Sensors 110

4.5.1 Quartz Crystal Microbalance 110

4.5.2 Surface Acoustic Wave Resonators 112

4.6 Optical Sensors 114

4.6.1 Colorimetric Sensors 114

4.6.2 Fluorescence Sensors 117

4.7 Electrochemical Sensors 120

4.7.1 Metal-Oxide Sensors 124

4.7.2 Graphene-Based Sensors 124

References 126

5 Nanofibers in Energy Applications 137
Caitlin Dillard and Vibha Kalra

5.1 Overview 137

5.2 Energy Storage Applications 142

5.2.1 Rechargeable Batteries 143

5.2.1.1 Lithium-Ion Batteries 145

5.2.1.2 Sodium-Ion 154

5.2.1.3 Beyond Li-Ion 155

5.2.2 Supercapacitors 160

5.2.2.1 Electric Double-Layer Capacitor (EDLC) 161

5.2.2.2 Pseudocapacitors 164

5.2.2.3 Separators 167

5.3 Energy Conversion Applications 167

5.3.1 Fuel Cells 169

5.3.1.1 Polymer Electrolyte Membrane Fuel Cell (PEMFC) 171

5.3.1.2 Alkaline Fuel Cell (AFC) 175

5.3.1.3 Solid Oxide Fuel Cell (SOFC) 176

5.3.2 Photovoltaics 178

5.3.2.1 Dye-Sensitized Solar Cells (DSSCs) 181

5.3.2.2 Perovskite Solar Cells 185

5.3.2.3 Organic Photovoltaic (OPV) 186

5.4 Concluding Remarks 190

References 192

6 Electrospun Nanofibers for Drug Delivery Applications 204
Zeynep Aytac and Tamer Uyar

6.1 Introduction 204

6.2 Methods for Encapsulation of Bioactive Molecules in Electrospun Nanofibers 206

6.2.1 Blend Electrospinning 206

6.2.1.1 Delivery of Drugs 206

6.2.1.2 Delivery of Proteins 213

6.2.1.3 Fast-Dissolving Electrospun Nanofibers 216

6.2.1.4 Stimuli–Responsive Nanofibers 221

6.2.2 Coaxial Electrospinning 226

6.2.2.1 Delivery of Hydrophilic Drugs 227

6.2.2.2 Delivery of Hydrophobic Drugs 229

6.2.2.3 Delivery of Proteins, Enzymes, and Growth Factors 230

6.2.2.4 Delivery of Multiple Drugs 233

6.2.2.5 Stimuli–Responsive Nanofibers 235

6.2.3 Emulsion Electrospinning 238

6.2.3.1 Single Electrospinning 239

6.2.3.2 Coaxial Electrospinning 242

6.3 Conclusion 246

References 247

7 Interfacing Electrospun Nanofibers with Microorganisms: Applications from Killing to Repelling to Delivering Living Microbes 257
Emily Diep, Jessica D. Schiffman, and Irene S. Kurtz

7.1 Introduction 257

7.2 Brief Background on the Electrospinning Process 258

7.3 Electrospinning Process and Variables 258

7.4 Why It Is Important to Understand the Interactions Between Biomaterials and Microorganisms 260

7.5 Background on Antibacterial Surface Engineering 261

7.6 Background on Antifouling Surface Engineering 262

7.7 Polymer Selection for Nanofibrous Biomaterials 263

7.8 Electrospinning Techniques Tailor the Location of Active Agents 264

7.9 Blend Electrospinning Yields a Dispersed Active Agent 265

7.10 Coaxial and Emulsion Electrospinning Enables the Controlled Delivery of Active Agents 266

7.11 Coating Electrospun Mats Tailors Their Interactions with Cells 267

7.12 Antibacterial Nanofiber Mats 268

7.13 Multifaceted Delivery from Nanofibrous Mats 270

7.14 Antifouling Nanofiber Mats 271

7.15 Nanofibrous Mats Containing Living Cells 273

7.16 Conclusion 275

Acknowledgments 276

References 276

8 Advances in Functionalizing the Interior and Exterior of Polymer Nanofibers 292
Richard J. Spontak, Bharadwaja S.T. Peddinti, Kristen E. Roskov and Xiaoyu Sun

8.1 Introduction 292

8.2 Nanofibers with Controlled Nanoparticle Distribution 295

8.2.1 Thermodynamic Considerations of Polymer Blends 295

8.2.2 Hybrid Nanofibers with Polymer Blends 297

8.2.3 Hybrid Nanofibers in Electromagnetic Fields 302

8.2.4 Anisotropic Nanoparticles in Flow Fields 304

8.3 As-spun Nanofibers with Bioresponsive Properties 307

8.3.1 Interior Incorporation of Antimicrobial Additives 307

8.3.2 Exterior Biofunctionalization of Polymer Nanofibers 309

8.4 Polymer Nanofibers with Postfunctionalized Surfaces 316

8.5 Nanofibers Produced by Directed Self-Assembly 321

8.6 Concluding Remarks 325

Acknowledgments 326

References 326

9 Nanofiber Aerogels: Bringing a Third Dimension to Electrospun Nanofibers 347
Tahira Pirzada, Vahid Rahmanian, and Saad A. Khan

9.1 Aerogels 347

9.1.1 Processing 348

9.1.2 Properties and Applications 349

9.1.3 Challenges 350

9.2 Nanofiber-Based Aerogels 350

9.2.1 Historical Background 351

9.2.2 Fabrication of Nanofiber-Based Aerogels (NFAs) 352

9.2.2.1 Electrospinning 352

9.2.2.2 Dispersion Preparation 357

9.2.2.3 Solid Templating 359

9.2.3 Applications 361

9.2.3.1 Filtration 361

9.2.3.2 Thermal Insulation 365

9.2.3.3 Building and Lightweight Construction 367

9.3 Future Perspectives 367

References 369

10 Micro and Nanofibers 374
Behnam Pourdeyhimi, Nataliya Fedorova, and Benoit Maze

10.1 Electrospinning 376

10.2 The Melt-blowing Process 377

10.2.1 The Reicofil Process 381

10.2.2 The Biax Multirow Process 384

10.2.3 The Hills Process 386

10.3 “Splittable” Bicomponent Fibers 387

10.4 Partially “Soluble” Bicomponent Fibers 393

10.5 Fibrillating Bicomponent Fibers 397

References 398

Index 406