Diversified Morphology of Electrospun Fibers through Self-Assembly of the Strings in the Jet Developed by Flow-Induced Phase Separation

Solution electrospinning produces not only round fibers but also many unexpected features, e.g., ribbons, nets, and fibers with beads, barbs, or branches along the fiber length. These diversified features are observed in the electrospun fibers of poly(vinyl alcohol), Nylon-6, poly(<i>N</i>-isopropylacrylamide), ultrahigh-molecular-weight polystyrene, and ultrahigh-molecular-weight polyethylene in this study. All these unique features could be realized through our recent discoveries that flow-induced phase separation occurs in the jet to develop polymer-rich phases of hierarchical string structures with various diameters. Subsequently, lateral association (or fasciation) of the hierarchical strings ensues and creates assembled strings of different kinds, which are split from the phase-separated jet and evolve into as-spun features after solvent evaporation. Our results indicate that flow-induced phase separation in jets cannot be overlooked and is likely to unify the formation mechanism of all diversified morphologies of electrospun products.