Nanoscale composites assembled on electrospun fibrous membranes

Polymer fibers with diameters less than 100 nm are readily fabricated by the electrospinning technique. By applying a large static voltage to a viscous polymer solution, the nanofibers can be collected as a non-woven fibrous membrane on an electrically grounded target. Such membranes possess a large interfacial surface area that can be used in a number of applications such as catalyst supports, chemical and biological sensors, filters, and dye-sensitized solar cells. To date, most of these applications cannot be realized due to limitations in the electrospinning technique. For example, not all polymers are readily electrospun. Also other materials, such as insoluble particles, cannot be electrospun alone, and when electrospun with a matrix polymer do not exhibit desirable properties.; This work has sought to overcome these shortcomings and extend the utility of the electrospinning technique. By combining electrospinning with other nanotechnologies including nanoparticles, electrostatic assembly of polyelectrolytes, liquid phase deposition of metal oxides, and surface polymerization of conjugated polymers, a large number of new nanostructures and devices are expected to be possible.; Titanium dioxide nanoparticles were blended with a spin-dope solution of poly(ethylene oxide). It was found that spin-dope viscosity was a major factor in defining the final fiber morphology during electrospinning and that the viscosity was not solely dependant on polymer concentration. Electrospun fiber diameter was found to be related to solution viscosity regardless whether the viscosity arose from particle addition or polymer concentration. The minimum polymer concentration required to electrospun was found to be the crossover concentration, provided additional viscosity came from another source, e.g. nanoparticles. This is the lowest polymer concentration at which chain entanglement occurs. Thus, nanofibers consisting of 80 percent by weight of TiO2 nanoparticles were fabricated.; Uniform coatings of metal oxides were deposited from an aqueous solution on electrospun nanofiber templates using liquid phase deposition. Titanium dioxide and tin dioxide were deposited and characterized. Modified surface chemistry affected the deposition rate by facilitating faster nucleation of the metal oxide domains. Carboxylic acid surface groups on a polyacrylonitrile (PAN) nanofiber were found to be most effective.; The surface functionalization of polyacrylonitrile nanofibers by immersion in a heated sodium hydroxide solution also facilitated electrostatic layer-by-layer assembly of polyelectrolytes on the nanofiber surface. Although, polyelectrolytes themselves can be electrospun, they cannot be used directly for layer-by-layer assembly because they dissolve when placed in the counter ion solution. Surface functionalization allowed for electrostatic assembly of polyelectrolytes, charged titanium dioxide particles, and the catalyst hematin directly onto the nanofibrous membrane due to the water-insoluble polyacrylonitrile core.; Electrostatically layered sulfonated polystyrene was used as a template for the surface polymerization of conjugated polymers in their conducting form. Enzymatic synthesis of polyaniline and a copolymer of pyrrole and EDOT was performed on electrospun nanofiber surfaces modified by electrostatic assembly of polyelectrolytes. Conductivity was measured and found to be on the order of 10-3 S/cm.; These results demonstrated the feasibility of extending the possible uses of electrospinning in new directions and for a host of new applications. A discussion of possible applications employing these combined techniques is presented.