Contents
Preface ix
Acknowledgments xi
1. Introduction to Electrospinning 1
1.1 Electrospinning 1
1.1.1 Brief History 2
1.1.2 Electrospinning Process and Principles 3
1.1.3 Fiber Morphology 10
1.2 Characteristics of Electrospun Nanofibers 12
1.3 Improved Electrospinning Techniques 13
1.4 Fiber-Collecting Modes 17
2. Emerging Applications of Electrospun Nanofibers 23
2.1 Biomedical 23
2.1.1 Tissue Engineering Scaffolds 23
2.1.2 Blood Vessels 24
2.1.3 Bones 27
2.1.4 Cartilages 29
2.1.5 Muscles 30
2.1.6 Skins 31
2.1.7 Neural Tissues 32
2.1.8 Other Tissue Scaffolds 34
2.1.9 Wound Healing 34
2.1.10 Drug Delivery and Release Control 37
2.2 Environmental Protection 39
2.2.1 Filtration 39
2.2.2 Metal Ion Adsorption and Recovery 41
2.3 Catalyst and Enzyme Carriers 43
2.3.1 Catalysts 43
2.3.2 Enzymes 45
2.4 Sensors 46
2.5 Energy Harvest and Storage 49
2.5.1 Solar Cells 49
2.5.2 Fuel Cells 51
2.5.3 Mechanical Energy Harvesters 52
2.5.4 Lithium Ion Batteries 53
2.5.5 Supercapacitors 56
2.5.6 Hydrogen Storage 57
2.6 Other Applications 58
3. Developments in Large-Scale Nanofiber
Electrospinning Systems 61
3.1 Downward Multi-Jet Electrospinning 61
3.2 Upward Needleless Electrospinning 66
3.2.1 Electrospinning Techniques 66
4. Upward Needleless Electrospinning with Disc, Ball,
and Cylinder Spinnerets 71
4.1 Cylinder Electrospinning 71
4.1.1 Effects of Applied Voltage and PVA
Concentration 72
4.1.2 Effect of Cylinder End Shape 74
4.1.3 Effect of Cylinder Diameter 75
4.2 Ball Electrospinning 76
4.3 Disc Electrospinning 77
4.3.1 Effects of Applied Voltage and PVA
Concentration 78
4.3.2 Effect of Disc Thickness 80
4.3.3 Comparison 81
5. Upward Needleless Electrospinning with Ring
and Coil Spinnerets 83
5.1 Ring Electrospinning 83
5.1.1 Single Ring 83
5.1.2 Multiple-Ring Spinnerets 86
5.2 Wire Coil Electrospinning 87
5.2.1 Conical Coil Electrospinning 87
5.3 Effects of Experimental Parameters on
Fiber Quality 89
5.3.1 PVA Concentration 89
5.3.2 Applied Voltage 90
5.3.3 Collecting Distance 91
5.4 Tubular Wire Coil Electrospinning 92
5.4.1 Spinning Process 93
5.4.2 Parameters Affecting Fiber Morphology 94
5.5 Effects of Coil Shape on Needleless
Electrospinning 95
5.5.1 Spinneret Length 95
5.5.2 Spiral Distance 96
5.5.3 Coil Diameter 97
5.5.4 Wire Diameter of the Coil 98
5.6 Effects of Experimental Parameters 98
5.6.1 Coil Rotating Speed 98
5.6.1.1 Applied voltage 98
5.6.2 Collecting Distance 99
5.6.3 PVA Concentration 100
5.7 Comparison 100
5.7.1 Needle and Coil Electrospinning 100
5.7.2 Multiple Rings and Coils 104
5.7.3 Comparisons of Different Nozzles 105
6. Electrical Field Analysis 109
6.1 Cylinder Electrospinning 111
6.2 Ball Electrospinning 115
6.3 Disc Electrospinning 117
6.4 Shaft-Linked Multiple Discs 121
6.5 Ring Electrospinning 123
6.6 Multiple Rings 129
6.7 Conical Wire Coil Electrospinning 130
6.8 Tubular Wire Coil 131
6.9 Comparison of Cylinder, Disc, Ring, and Coil 132
6.10 Collectors 135
7. Fiber Collection 137
7.1 Effect of Collector Shape 137
7.2 Effect of Collection Media 139
7.3 Effect of Collecting Distance 140
7.4 Effect of Air Flow 141
8. Conclusion and Outlook
Index 187
Preface
Electrospun nanofibers have shown enormous application potential in diverse areas. However, most works on electrospinning nanofibers are based on conventional needle electrospinning techniques, and mass production of nanofibers for practical applications has been a great challenge with the needle electrospinning systems. This book systemically introduces a relatively new electrospinning process, needleless electrospinning. The book is divided into seven chapters. In the first chapter, basic electrospinning theory is introduced. The second chapter summarizes the functional applications of electrospun nanofibers in different fields. Chapter 3 reviews the emerging electrospinning technologies that have potential for large-scale production of nanofibers. Chapters 4 and 5 describe an important needleless electrospinning technique using different fiber generators such as ball, cylinder, disc, and wire coil, and the effects of the fiber generator, its shape and dimension, and operating parameters on electrospinning performance, fiber morphology, and productivity are also introduced. Chapter 6 analyzes the electric field profiles and provides a method to calculate the electric field intensity in an electrospinning zone. Chapter 7 discusses the influence of the fiber collector on fiber quality. The book will be a very useful resource for academics, industry professionals, and graduate students in nanomaterials, nanostructures, and nanofabrication.
Chapter 1
Introduction to Electrospinning
Nanofibers are defined as one-dimensional nanomaterials with diameters less than 1 μm (1000 nm), and an aspect ratio (length/ diameter) larger than 100:1. They are also named as superfine or ultrathin fibers in some literature [1, 2]. When the fibers are in the range of 100–1000 nm, they are also referred to as submicron fibers [3–5]. This intrinsic feature offers them drastically increased surfaceto- volume ratio and high aspect ratio. There are several methods to produce nanofibers, including phase separation [6], self-assembly [7, 8], template synthesis [9], melt-blowing [10], flash spinning [11], bicomponent spinning [12], and electrospinning [13, 14]. Nanofiber mats produced from electrospinning have a naturally formed porous structure with excellent pore interconnectivity, and the pores are in the range between tens of nanometers to a few micrometers. The open pore structure and high permeability to gas, along with the high surface area, make them ideal porous membranes. Compared with other one-dimensional nanostructures (e.g., nanotubes or nano-rods), continuous nanofibers are advantageous in terms of fabrication cost and the possibility of being integrated into other desired assembly in one step.