Temperature-dependent conductivity of conducting polymers exposed to gases

We have made measurements of the effect of water vapour, oxygen and nitroge n on the temperature-dependent conductivity of polypyrrole gas sensors. Oxy gen and nitrogen had little effect, while water vapour decreased conductivi ty and increased conductivity temperature dependence, consistent with decre ased hopping between localized states. No evidence was found of any metalli c term in the conductivity of our polypyrrole samples, in strong contrast t o the case of polyaniline. We analyze previous conductivity measurements Fo r polyaniline exposed to the same gases, showing that the conductivity rema ins consistent with the general expression for polymer conductivity with a significant metallic term.