The effect of processing variables on the morphology of electrospun nanofibers and textiles

Electrospinning is a process that produces continuous polymer fibers with diameters in the sub-micron range through the action of an external electric field imposed on a polymer solution or melt. Non-woven textiles composed of electrospun fibers have a large specific surface area and small pore size compared to commercial textiles, making them excellent candidates for use in filtration and membrane applications. While the process of electrospinning has been known for over half a century, current understanding of the process and those parameters, which influence the properties of the fibers produced from it, is very limited. In this work, we have evaluated systematically the effects of two of the most important processing parameters: spinning voltage and solution concentration, on the morphology of the fibers formed. We find that spinning voltage is strongly correlated with the formation of bead defects in the fibers, and that current measurements may be used to signal the onset of the processing voltage at which the bead defect density increases substantially. Solution concentration has been found to most strongly affect fiber size, with fiber diameter increasing with increasing solution concentration according to a power law relationship. In addition, electrospinning from solutions of high concentration has been found to produce a bimodal distribution of fiber sizes, reminiscent of distributions observed in the similar droplet generation process of electrospray. In addition, we find evidence that electrostatic effects influence the macroscale morphology of electrospun textiles, and may result in the formation of heterogeneous or three-dimensional structures.