| Electrospinning is a straightforward method to produce novel fibers with diameters ranging downward from typical textile fiber by two or three orders of magnitude. In this study, several kinds of high performance polymers, including Poly(meta-phenylene isophthalamide) (MPD-I), polyetherimide and poly(vinylidene fluoride), were electrospun from solution to form nanofibers. Scanning and transmission electron microscopic images show ultra-thin web-like fibers, ribbon-like fibers and branching fibers, demonstrating a variety of morphological features produced by electrospinning. MPD-I nanofibers typically had diameters around 100 nm. The diameter of the smallest NOD-I fiber observed was 4 nm. The fiber surface was featureless at a resolution of about one nanometer. The as-spun fibers had an imperfect crystal structure which was improved by annealing. The wide angle X-ray and electron diffraction pattern of the MPD-I nanofibers, after annealing, was similar to that of MPD-I textile fibers.; Electrospun nanofibers can be used as either functional or sacrificial substrates for creating nanoscale structures. Surface properties of electrospun nanofibers are of importance for applications in the areas of filtration, composites, biomedicine and electronics. Chemical vapor deposition and physical vapor deposition are straightforward methods for modifying the surface properties of nanofibers. The MPD-I nanofibers were successfully coated with carbon, copper and aluminum by these processes. MPD-I fibers, coated with aluminum, were used as templates for nanotube synthesis. Nanotubes of mixed aluminum oxide and aluminum were produced by pyrolytic degradation of the MPD-I nanofiber cores. The aluminum coating layers underwent only a limited degree of oxidation during pyrolysis of the MPD-I. The aluminum coating layers did not change when the template fiber was removed by dissolution. The average inner diameter of the tubes was around 100 nm. The smallest observed inner diameter of a tube was around 25 nm.; The development of nanofibers as coalescing filter media is of industrial and academic interest. Aerosol droplets become attached to surfaces of the filter media. The high surface area per unit mass of nanofibers makes them very effective for the collection of small droplets. Observation with an optical microscope provides a direct way to study the capture and coalescence of aerosol droplets passing through a network of nanofibers. Surface tension causes the oil collected on a fiber to form small beads. As more droplets are collected, the beads grow larger, combine in complex ways, move along the fibers, connect fibers at crossing points, and finally drain out of the network. The time development of these various processes was correlated with mathematical models. The effect of thermal gradients on the motion of droplets was also observed and correlated with thermocapillary Marangoni convection. Such phenomenon may assist in the drainage of oil droplets from a filter. |
