Bead structure variations during electrospinning of polystyrene

One of the attractive features of electrospinning is the capability to produce a wide range of fiber morphologies by controlling various material and process parameters. Other than the typically observed cylindrical fibers, flat, wrinkled, and porous fibers have been reported to date for different polymer-solvent systems. Koombhongse et al. suggest that the morphology of the fiber obtained is determined by a complex interaction between fluid flow, electrical forces, and solvent evaporation. During the solidification of the jet, a thin skin of solid polymer can form on the surface, especially if a highly volatile solvent is used. This skin can subsequently collapse and lead to wrinkled and flat fibers. The formation of sub-micron pores on electrospun fibers is another interesting phenomenon, which has attracted attention. Reports have shown that humidity, molecular weight and solvent properties play an important role in pore formation. A recent study by Liu and Kumar indicates that droplets of solution produced by electrospinning can also undergo skin formation and collapse, thereby developing interesting bead shapes and surface morphologies. A variety of bead morphologies including porous beads, microscopic ladles and cups can be produced by using different solvents. Although these results confirmed the significance of solvent evaporation rate and solution viscosity on bead morphology, the effect of molecular weight on attainable bead structures has not yet been explored. The ability to control the bead structures in terms of this fundamental parameter may be important in many industrial polymers for diverse applications including aerosols, surface coatings, membranes, chromatography standards and drug delivery systems. The purpose of this contribution is to examine the cumulative effects of polymer molecular weight and solution concentration on the bead structure in electrospun polystyrene. The structures that may be produced with dilute solutions before the emergence of stable fiber structures are explored.