Temperature-dependent conductivity of conducting polymers exposed to gases*

We have made measurements of the effect of water vapour, oxygen and nitrogen on the temperature-dependent conductivity of polypyrrole gas sensors. Oxygen and nitrogen had little effect, while water vapour decreased conductivity and increased conductivity temperature dependence, consistent with decreased hopping between localized states. No evidence was found of any metallic term in the conductivity of our polypyrrole samples, in strong contrast to the case of polyaniline. We analyze previous conductivity measurements for polyaniline exposed to the same gases, showing that the conductivity remains consistent with the general expression for polymer conductivity with a significant metallic term.