Phase morphology control in electrospun nanofibers from the electrospinning of polymer blends

Electrospinning of polymer blends offer the potential to prepare functional nanofibers for use in a variety of applications. The ability to control the phase morphology to obtain the nanofibers with special structures has received relatively little investigation. This research focuses on phase morphology control of electrospun nanofibers from the electrospinning of polymer blends. The first study investigated the internal morphology of nanofibers prepared by electrospinning polybutadiene (PB)/polycarbonate (PC) blends. Co-continuous and core-sheath structures were observed by TEM. The composition ratio, molecular weight, solution concentration and solvent type were changed to investigate how these factors affected the resulting phase morphology within the nanofiber. The phase morphology of nanofibers from PB/PC blends were found to depend not only on the composition ratio of the blends, but also on the molecular weight of individual polymer components. Decreasing molecular weight of either the polycarbonate or the polybutadiene is helpful to form core-sheath rather than co-continuous structures under the rapid solvent evaporation that occurs during the electrospinning process. The low viscosity of the blending system at high concentration before solidification is the prerequisite condition for the formation of core-sheath structures.; In the second study, core-sheath nanofibers with conductive polyaniline as the core and an insulating polymer as the sheath were prepared by electrospinning blends of polyaniline with either polystyrene or polycarbonate. When polyaniline was blended with polymethyl methacrylate and polyethyl oxide, only isolated domains of polyaniline in beadlike structures were formed. The beadlike structures are thought to result from the high surface tension of the solution. The low molecular weight of PANI was found to play a key role in the formation of core-sheath structures, as opposed to co-continuous morphologies.; The last part gives a detailed investigation of the effect of thermodynamic and kinetic factors on the formation of core-sheath structures in electrospun nanofibers. It was found that the formation of core-sheath structures depends on interaction of thermodynamic, kinetic and rheological factors. The incompatibility and large solubility parameter difference of two phases is helpful, but not sufficient for the formation of core-sheath structures. Kinetic factors, however, play a more important role in the development of the nanofiber morphology. During the electrospinning process, the rapid solvent evaporation requires systems with high molecular mobility. It was found that polymer blends with lower molecular weight tend to form core-sheath structures rather than co-continuous structure, as a result of their higher molecular mobility. Rheological factors also affect the internal phase morphology of nanofibers. It was observed the composition with higher viscosity was always located at the center and the composition with lower viscosity located outside.