The effect of processing variables on the morphology of electrospun nanofibers

The electrospinning is a straightforward way to produce ultrafine fibrous membranes from polymer solutions or melts under a high electric voltage. In the electrospinning process, some parameters such as polymer concentration,... [ view full abstract ]

The electrospinning is a straightforward way to produce ultrafine fibrous membranes from polymer solutions or melts under a high electric voltage. In the electrospinning process, some parameters such as polymer concentration, feeding rate of the polymer solution, additives, humidity, viscosity, surface tension, applied voltage, and nozzle-to ground collector distance will affect the fiber diameter and morphology. The aim of present work is to investigate the effects of processing parameters including the spinning voltage and solution concentration on the morphology of the fibers formed. The solutions used in the electrospinning experiments were prepared using Poly(vinylidene fluoride) (PVDF). This material was dissolved in N,N-dimethylformamide (DMF) to make solutions with concentrations ranging from 16 to 20 wt%. These solutions were spun from a 5 ml plastic syringe connected to a nozzle using a plastic hose (2 mm in diameter) then clamped to a ring stand that was 15 cm above a grounded metal screen and using voltages ranging from 16.0-20.0 kV. Optical micrographs of electrospun fiber mats produced were taken with a Nikon Eclips E400. Effects of PVDF/DMF concentrations on morphology of the nanofibers formed are shown in Fig. 1. These images demonstrate that formation of the fiber depends on the polymer concentration. The increase in the polymer concentration caused beads on the string disappeared and morphology of the fibers produced becomes more uniform and continuous. 

The effect of applied voltage on morphology of the nanofibers formed can be seen at Fig. 2. As voltage is increased, the electrospun fibers produced have essentially a cylindrical morphology, but there is a distinct decrease in number of bead defects present in the fiber mat. At 20.0 kV, the morphology of the fibers produced becomes more uniform, the bead defects are lost and the fibers are continuous.

Increasing the applied voltage increased the force that overcomes the surface tension of the polymer solution. This will also increase the amount of polymer sprayed during the ESD process.