Electrospun conducting polymer composites for chemo-resistive environmental and health monitoring applications

The focus of this dissertation is the development of polyaniline based hybrid systems for selective room temperature detection of NO2. The electrospinning technique has been employed to produce highly dispersed nanocomposites of leucoemeraldine base polyaniline (LEB-PANI) with poly-vinyl-pyrrolidone (PVP) and cellulose acetate (CA) as secondary components. The nanocomposites exhibit relatively high sensitivity and selectivity to NO2 down to 0.5 ppm with response times down to 40 s and recovery times down to 155 s at varying levels of humidity.;DC electrical resistance measurements reveal that the responses of the LEB-PANI composites have dependence on the humidity level and concentration of LEB-PANI in the composite matrix, whereas at low concentrations the resistance decreases on exposure.;to NO2, for a 1:1 PVP LEB-PANI ratio there was no response to NO2, and for high LEB-PANI concentrations the resistance increased on exposure to the analyte. The varying response mechanisms are attributed to the oxidation state and degree of water absorption by PVP and LEB-PANI. DC electrical resistance measurements of the CA LEB-PANI composite during exposure to the analyte suggest that the response mechanism has dependency on the humidity level in the gas chamber such that on exposure to NO 2 the electrical resistance of the film decreases. This is partly attributed to the hydrolysis of CA yielding acetic acid which lightly dopes polyaniline and acts as an additional reactant site along the polymer backbone for NO 2.;An in-situ gas sensing ultraviolet-visible spectroscopic technique was developed to analyze the effects of processing and the sensoric nature of the LEB-PANI composites. Absorption spectra of the PVP LEB-PANI composites reveal that as the concentration of LEB-PANI increased the oxidation level increased from the reduced state to the emeraldine oxidation state, as evaluated against the work of MacDiarmid et al. The oxidation level of the CA LEB-PANI composite films also exhibited an increase in the oxidation level to the emeraldine oxidation state.;The evolution of the electronic transitions in the films were analyzed at different levels of humidity and under exposure to NO2 revealing that for the PVP LEB-PANI composites, water vapor absorbed into the electrospun mat and adsorbed on LEB-PANI (via H-bonding and protonation of amine and imine sites, respectively) acts as a primary charge carrier for polyaniline (through the formation of polarons and bipolarons). This charge transport mechanism of hydrated LEB-PANI is shown to be analogous to the Grotthus mechanism for proton transport.;The observations relative to effects of NO2 exposure reveal the existence of several reaction mechanisms between LEB-PANI and NO 2: (1) NO2 can oxidize the polymer transferring an electron from the N center to the gas, and (2) NO2 can be dissolved by the water vapor producing H3+O, HNO2, and NO2- which can both reduce and protonate imine sites of LEB-PANI. The latter affects to the stability of the sensors.;These studies coupled with x-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR) of the films, are used to determine the proper paradigm for NO2 detection with LEB-PANI.