4. Self-assembly

#### 5.Electrospinning

Commonly nanofiber fabrication is done by electrospinning method [19].

### 1.1.1 Drawing

In drawing process, single nanofiber is attended by stretching of polymer that is in solution form. With this method only viscoelastic materials have been spun into nanofibers. If polymer is in melt form, then cooling system is necessary to solidify the fiber. On the other hand, if polymer is in solution form, then heating mechanism is necessary to evaporate the solvent. This is a very slow process that is suitable only for lab scale [18]. Process diagram is shown in Figure 3.

that have diameter equal to size of porous [20]. The process diagram is shown

extraction of solvent, freezing, and freeze-drying. Fiber dimensions are not

In this process, five steps are involved: polymer dissolution, polymer gelation,

in Figure 4.

231

Temple synthesis [20].

Figure 4.

Figure 3.

Drawing in method [19].

Classification of Electrospinning Methods DOI: http://dx.doi.org/10.5772/intechopen.88654

1.1.3 Phase separation

#### 1.1.2 Template synthesis

In this method, nonporous membranes are used in which pores are in cylindrical form. Diameters of these pores are uniform. Solid polymers are formed Classification of Electrospinning Methods DOI: http://dx.doi.org/10.5772/intechopen.88654

that have diameter equal to size of porous [20]. The process diagram is shown in Figure 4.

#### 1.1.3 Phase separation

In this process, five steps are involved: polymer dissolution, polymer gelation, extraction of solvent, freezing, and freeze-drying. Fiber dimensions are not

4. Self-assembly

1.1.1 Drawing

Figure 2.

Figure 1.

Consumptions of nanofibers in world [18].

Nanorods and Nanocomposites

5.Electrospinning

Potential applications electrospun nanofibers [18].

1.1.2 Template synthesis

230

Commonly nanofiber fabrication is done by electrospinning method [19].

In this method, nonporous membranes are used in which pores are in cylindrical form. Diameters of these pores are uniform. Solid polymers are formed

only for lab scale [18]. Process diagram is shown in Figure 3.

In drawing process, single nanofiber is attended by stretching of polymer that is in solution form. With this method only viscoelastic materials have been spun into nanofibers. If polymer is in melt form, then cooling system is necessary to solidify the fiber. On the other hand, if polymer is in solution form, then heating mechanism is necessary to evaporate the solvent. This is a very slow process that is suitable controllable with this process. This proves only suitable for lab scale [21]. The process diagram is shown in Figure 5.

1.1.5 Electrospinning

2. Syringe pump

4.Metal collector

Figure 7.

233

Needle electrospinning.

Instruments used for electrospinning are given below:

schematic diagram of the complete electrospinning setup.

3. Spinneret (a small diameter needle connected to the syringe)

The polymer is dissolved in a solvent before electrospinning, and when it is completely dissolved, it forms polymer solution. The polymer fluid is then introduced into the syringe tube for electrospinning. The positive terminal of the DC power supply is connected to the hollow needle [23], and the negative terminal is connected to the metal collector. With the increase of intensity of the electric field, the repulsive electrostatic force overcomes the surface tension, and the charged jet of the fluid is ejected from the tip of the Taylor cone. The discharged polymer jet undergoes an instability and elongation process, which allows the polymer in the jet to become very long and reduces the diameter of the extruded polymer fiber. The solvent that is used to dissolve the polymer evaporates, and the polymer in the jet is dried. The solvent evaporation depends on the distance between the tip and collector, the solution vapor pressure, and the inside chamber temperature. Stable environmental conditions are therefore important in getting good quality nanofibers. The maximum applied voltage for a needle electrospinning setup is normally less than 30 kV and is also highly humidity dependent [24]. Figure 7 illustrates the

Needleless electrospinning presented as an option electrospinning innovation that deliver nanofibers on a substantial scale. Needleless electrospinning is included as electrospinning of nanofibers straightforwardly from an open fluid surface. Many planes are shaped at the same time from the needleless fiber generator (spinneret) without the impact of capillary effect that is regularly connected with needle electrospinning. Since the fly start in needleless electrospinning is a selfcomposed process which happens on a free fluid surface, the spinning process is hard to control. In needleless electrospinning process, many shapes of spinneret

1.High-voltage DC power supply

Classification of Electrospinning Methods DOI: http://dx.doi.org/10.5772/intechopen.88654
