We devote a whole chapter to fibers produced by a process called electrospinning. Although the process is thought to have originated in the early twentieth century, it was not until 1995 when Doshi and Reneker (1995) sort of rediscovered the process and used the term electrospinning for the process. Reneker and his group are credited with pointing out the diverse range of applications for electrospun nanofibers. It is a very versatile technique for making nanofibers, generally polymeric fibers although ceramic fibers have also been made by this technique. Most electrospun fibers are nanofibers because their diameters are less than 100 nm. There has been a tremendous increase in the use of the electrospinning technique and applications of nanofibers produced in fields as diverse as health care and filtration in aggressive environments (Laudenslager and Sigmund, 2015). The starting material can be in solution form or melt form. There are essentially three components in the process: a high voltage supply, a capillary tube with a needle, and a screen to collect the fibers. The high voltage creates an electrically charged jet of polymer solution or melt out of the needle. The solvent in the jet evaporates (or if a melt is used, it solidifies) and an interconnected web of small fibers is collected on the collector screen. Initially, this technique was used for making polymeric nanofibers. The technique has been used for the preparation of metal oxide/ceramic nanofibers; e.g., silica, zirconia, titania, nickel oxide, barium titanate, lead zirconate titanate, and other oxide materials (Ramakrishna et al., 2005).

It turns out that fibrous nanomaterials or nanofibers as processed by electrospinning are attractive for many applications because of their intrinsically high porosities and large surface areas. Porosity or voids in materials, as highlighted by Gladysz and Chawla (2014), are not always undesirable. Electrospinning is a simple, versatile technique for generating nanofibers from a variety of materials.

In this chapter, we describe the basic process of electrospinning, followed by some examples of nanofibrous structures produced by this process and applications of electrospun nanofibers.

Basic process

Under the action of an electrostatic field, a droplet of a conducting polymer solution at the tip of a capillary is deformed into a conical shape; this shape is called the Taylor cone. The Taylor cone is formed because of equilibrium between the surface tension of the droplet and the applied electric field. Figure 5.1 shows the Taylor cone schematically.