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

Electrospinning is a process that produces continuous polymer fibers with d iameters in the sub-micron range through the action of an external electric field imposed on a polymer solution or melt. Non-woven textiles composed o f 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 electrospinni ng has been known for over half a century, current understanding of the pro cess and those parameters, which influence the properties of the fibers pro duced from it, is very limited. In this work, we have evaluated systematica lly the effects of two of the most important processing parameters: spinnin g voltage and solution concentration, on the morphology of the fibers forme d. 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 densit y increases substantially. Solution concentration has been found to most st rongly affect fiber size, with fiber diameter increasing with increasing so lution concentration according to a power law relationship. In addition, el ectrospinning from solutions of high concentration has been found to produc e a bimodal distribution of fiber sizes, reminiscent of distributions obser ved in the similar droplet generation process of electrospray. In addition, we find evidence that electrostatic effects influence the macroscale morph ology of electrospun textiles, and may result in the formation of heterogen eous or three-dimensional structures. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.