James D. Kleinmeyer

Abstract : Non-woven fabrics composed of nanofibers have a large specific surface area and small pore size compared to commercial textiles. These properties make such non-woven fabrics excellent candidates for filter and membrane applications, particularly in the areas of chemical and biological agent defense. Nanofibers may be produced by electrospinning, which uses an electric field to produce continuous fibers with diameters in the tens of nanometers range. Although the technique has been known for some time, very little information concerning the effect of processing variables such as solution concentration, viscosity, surface tension, flow rate and acceleration voltage on final fiber properties exists in the literature. In this work, nanofibers of polyethylene oxide have been electrospun from a range a solution concentrations and for a range of voltages. Wide angle X-ray diffraction and differential scanning calorimetery indicate that crystal structure is poorly developed in the electrospun fibers, when compared to results obtained from poly(ethylene oxide) powder. Fiber diameter increases with increasing concentration by the 0.53 power. We find that for concentrations of 8% (wt) and greater, a bimodal fiber diameter distribution has been observed, which is analogous to results reported for electrospray experiments. The density of node defects has been shown to increase with increasing voltage for a constant solution feed rate.

Electrospinning is a process by which submicron polymer fibers can be generated through use of an electrostatically driven jet of polymer solution. Use of electrospun nanofibers in electronic, biomedical, and protective clothing applications often involves the incorporation of some sort of functionalized particulate (i.e. carbon nanotubes, activated carbon, clay silicates, etc.). The current work uses conventional and high speed imaging techniques to study the motion of particles in the linear portion of electrostatically driven jets of Polyethylene oxide/water solutions. Observation of the motion of carbon particles using conventional video reveals the presence of eddy currents in the meniscus from which the jet originates. High-speed video of the motion of urethane particles in the liquid jet has been used to measure jet velocities, which range from 1-2 meters/second depending on initial processing conditions. The effect of solution viscosity, field strength, and flow rate on jet velocity and shear rate have implications for the scale up of the electrospinning process and are discussed in detail.