In 1934, Formhals patented a process to produce polymer filaments using electrostatic force. Later on, the process evolved and was named as electrospinning [79�C81]. This method is able to produce continuous Tipifarnib cancer nanofibers from polymer solutions or melts in the presence of high electric fields, in the region of 10�C30kV. So far, hundreds of polymers have been successfully fabricated by electrospinning process [87]. Thermoelectric polymers like carbon nanotube (CNT)/polyaniline (PANI) composite, polyaniline/(polystyrene and polyethylene Oxide) blends, polyaniline, polypyrrole, and polycarbonate nanofibers have been successfully fabricated through electrospinning process [57]. The basic schematic setup for the electrospinning process is shown in Figure 11. Figure 11A basic electrospinning setup [88].

In the electrospinning process a charged liquid polymer solution is introduced into an electric field. A high voltage (HV) direct current (DC) power supply is used to generate the potential differences in the range between 10 and 30KV. A needle attached to a syringe is used to dispense the liquid polymer solution at a desired voltage between 10 and 30kV. After that it is deposited on a collector which is grounded. The cathode of the HV power supply is attached to a wire and inserted into the syringe containing the polymer solution and the anode is attached to the ground. A rotating drum, usually wrapped with aluminum foil can be used as a collector. The tip to collector distance is maintained between the ranges of 10�C30cm. The inner diameter of a needle can be between 0.5�C1.

5mm. The ejected polymer solution forms a continuous nanofiber when the high voltage overcomes the surface tension. Once the ejection starts, at the tip of the needle, the pendant droplet of the polymer solution forms a conical shape, typically referred to as Taylor cone. Whilst the fluid is charged, the surface charge and the surface tension operate in opposite relation. Therefore, the fluid changes shape and the formed structure is known as the Taylor cone [89]. The images of the formation of a Taylor cone are shown in Figure 12.Figure 12Formation of the Taylor cone [89].The key parameters which affect the formation of nanofibers are (1) solution parameters such as viscosity, conductivity, surface tension, and vapor pressure; (2) process parameters such as shape of collector, needle diameter, solution flow rate, tip to collector distance, and applied voltage; (3) ambient parameters such as solution temperature, humidity, and air velocity in the electrospinning chamber.

By varying these parameters the thickness and smoothness of the fibers can be controlled [90]. A typical SEM micrograph of an electrospun nanofiber (Polypyrrole) is shown in Figure 13.Figure 13SEM micrographs of a polypyrrole electrospun nanofibers, formed from aqueous solutions of 1.5wt% poly(ethylene oxide) as carrier, Cilengitide with (a) and without (b) 0.5wt% Triton X-100 surfactant.