| Using a new interfacial polymerization method for the synthesis of polyaniline nanofibers, both nanofiber sensors and conventional polyaniline sensors are compared. Five different response mechanisms are explored: acid doping, base dedoping, reduction, swelling, and polymer chain conformational changes. In all cases, the polyaniline nanofibers perform better than conventional thin films. Their high surface area, porosity and small diameters enable rapid and facile diffusion of molecules and dopants into the nanofibers.;A new sensor for hydrazine detection is reported using conventional polyaniline thin films processed from hexafluoroisopropanol. This and other fluorinated alcohols are shown to react with hydrazine to produce a very strong acid, HF. The hydrofluoric acid protonates the emeraldine base form of polyaniline leading to large increases in conductivity. In contrast, conventional polyaniline films processed from other organic solvents and polyaniline nanofiber films processed from water become more insulating upon exposure to hydrazine because hydrazine acts as a strong reducing agent, converting the emeraldine form of polyaniline to its leucoemeraldine oxidation state.;The ability to control and enhance the response of polyaniline nanofibers to molecules like hydrogen sulfide is demonstrated through the formation of new nanostructured, conducting organic/inorganic hybrid materials. Polyaniline nanofiber composites with transition metal chlorides have a remarkable response to hydrogen sulfide that is 4 orders of magnitude greater than the corresponding unmodified nanofibers. The observed response is correlated with the stability of the resulting metal sulfide with Cu > Cd > Zn as indicated by the solubility product constants (Ksp) for the metal sulfides.;Copper acetate and related metal salt films react with hydrogen sulfide to form metal sulfide films directly at room temperature resulting in very large conductivity changes (over 8 orders of magnitude) induced by parts per million hydrogen sulfide. Direct electrical measurement of this transformation can be used as a method for monitoring trace amounts of hydrogen sulfide.;Humidity appears to enhance both the sensor time response and sensor response level due to the enhanced charge transfer phenomena that water produces upon contact with polyaniline. In addition to sensors, polyaniline nanofibers can also be used as hydrogen storage materials. |
