The electrospinning process and applications of electrospun fibers

An electrospinning process that produced ultra small sized fibers using only electrostatic force as the driving force was designed, developed, and characterized.; In the electrospinning process an electric field is used to create a charged jet of the polymer solution. As this jet travels in air, the solvent evaporates leaving behind charged polymer fiber, that can be electrically accelerated and/or deflected, and collected on a metal screen.; Fibers with a variety of cross sectional shapes and sizes with diameters in the range of 0.05 microns to 5 microns were successfully electrospun from various classes of polymers, such as water soluble, polyesters, liquid crystalline, and biopolymers.; Several process parameters were identified and characterized using aqueous solutions of the poly(ethylene oxide) varying in molecular weight. The relationship between the spinnability of the solutions and the molecular weight of the polymer were determined. A mathematical model was built to describe the force balance in the electrospinning process. Forces acting on the jet were identified and calculated.; Large elongational flows in flows in short times using strong applied forces are desired in the fiber spinning process. Associated with the fiber formation is the disentanglement of the polymers in solution or in the melt. The extensional viscosity at the tip of the cone was determined in the electrospinning process. Entanglements in a polymer solution are greatly affected by the concentration of the solution. The role of entanglement is important in the flow behavior of long chain polymer in solution. Theoretical calculations were made to investigate the crossover concentration (C*) from the electrospinning experiments.; In order to understand the electric fields involved in the process, finite element calculations were performed. The magnitude and direction of the electric field, the equipotential lines, and the force vectors driving the charged jet in the electrospinning geometry were determined.; The structure and morphology of the electrospun fiber were investigated using optical, scanning electron, and atomic force microscopes.; Because of the commercial interest in the electrospun fibers, commercial applications are still being explored. Some of the applications of the electrospun fibers investigated in this research are discussed in this dissertation.