Electrospun conducting nanofiber-based materials and their characterizations effects of fiber characteristics on properties and applications /

by Aussawasathien, Darunee.

The advantages of conducting materials in the non-woven nanofiber-mat form prepared by the electrospinning technique are proposed for sensing nanocomposite applications. Due to the sub-micron size of electrospun conducting fibers, a large specific surface area is generated, while the fiber web contains high fiber aspect ratio and high interconnecting network compared to the same materials in film and short fiber forms. Consequently electrospun lithium perchlorate doped polyethylene oxide (LiClO4doped PEO) fibers and electrospun carbon black filled LiClO4-doped PEO composite fibers were prepared to be used as humidity sensors. The measurements of humidity dependent resistance of these conducting fibers were carried out for different humidity changes. Electrospun camphosulfonic acid doped polyaniline-polystyrene (HCSA doped PANI-PS) fibers were also produced for glucose sensing measurements. Glucose oxidase (GOX), an enzyme, was immobilized on as-spun fiber surfaces prior to glucose sensing detection. Pristine H2O2 solution was used for testing the glucose sensing electrode composed of HCSA doped PANI-PS fibers. The cyclic voltammetry method was used to detect the redox currents for varied glucose concentrations at the oxidative potential of the glucose oxidation. The surface morphology before and after sensing measurements of as-prepared fibers for both types of sensors were investigated. Sensitivity comparison was performed between the fiber and film-type sensors as indicated by the slopes of iii humidity versus logarithm of resistance lines and glucose concentration versus redox current lines. Electrospun polyacrylonitrile (PAN) fiber precursor based carbon fiber (CNF) as well as electospun nickel (Ni) nanofiber-based mats were also produced and impregnated with epoxy resin. The electrical and mechanical properties of as-prepared nanofibers in the mat and short fiber filled epoxy nanocomposite forms were determined to demonstrate the effect of fiber aspect ratio and interconnecting network on those properties. Furthermore, the improvement of CNF conductivity was achieved by using in-situ silver (Ag)-PAN fibers as precursors, as well as by chemically coating Ag on CNF mat surfaces. For electrospun Ni nanofibers, Ag was chemically coated on fiber surfaces to prevent metal oxidation, and to increase conductivity. The characterization of samples was performed by using scanning electron microscope (SEM), Raman spectrometer, wide angle x-ray diffractometer (WAXD), Thermal gravimetric analyzer (TGA), Fourier transform infrared spectrometer (FT-IR), dynamic mechanical analyzer (DMA), voltmeter, and tensile tester. The effect of high thermal conductivity of CNF mat on curing reaction of epoxy nanocomposites was also studied by isothermal and dynamic experiments using DSC together with the gel content determination. Kamal’s model was employed for curve fitting the conversion rate versus the reaction rate at the initial stages of curing, at low temperatures. iv