Electrospinning

Electrospinning is a widely used technique for the electrostatic production of fibers, during which electric power is used to make polymer fibers with diameters ranging from 2 nm to several micrometres from polymer solutions or melts. This process is a major focus of attention because of its versatility and ability to continuously produce fibers on a scale of nanometres, which is difficult to achieve using other standard technologies.

The principle of electrospinning

The main principle of the ES process is the effect that high voltage has on a polymer solution.
The basic ES system consists of three parts:

• a source of high voltage

• a spinneret

• a grounded collector

High voltage (tens of kV) is connected to the end of a capillary containing liquid solution. Once the electric field intensity increases, the hemispherical surface of the liquid at the end of the capillary extends and creates a conical shape known as a Taylor cone. By increasing the electric field further, the critical value at which the repulsive electrostatic force overcomes the surface tension is reached, and the charged strand squirts out of the end of the Taylor cone. The strand of polymer solution undergoes a process of instability and lengthening, during which solvent evaporates. The fibers are then deposited on the collector. The resulting product is a non-woven fibrous layer.

In the classical electrospinning arrangement, nanofibers are deposited on the collector at random. For some applications, however, an ordered structure is more appropriate. The method used to organize the nanofibers can be influenced by the type of collector.
Electrospinning is a relatively simple way of creating nanofiber materials, but there are several parameters that can significantly influence the formation and structure of the nanofibers. These parameters are generally divided into three groups: solution, process and ambient parameters.

SOLUTION

• Viscosity

• Solution concentration

• Molecular weight of the polymer

• Solvent properties

• Surface tension

• Conductivity

PROCESS

• Voltage applied

• Distance of the electrode from the collector

• Flow rate

• Capillary geometry

AMBIENT

• Temperature

• Relative humidity