Electrical conductivity response of polypyrrole to acetone vapor: effect of dopant anions and interaction mechanisms

The chemically prepared undoped polypyrrole (PPy) and the PPy doped with seven dopant anions, at a dopant to monomer molar ratio of 1/12, were used as chemical sensors to detect acetone vapor. The negative changes in specific conductivity, Deltasigma, of PPys upon exposed to acetone vapor were observed. The magnitudes of Deltasigma depend critically on the type of the dopants which induces different properties amongst doped PPys. For the sulfonate doped PPy, Deltasigma depends exponentially on the doping level (N+/N) and on the initial specific conductivity. It also depends linearly on the proportions of the bipolaron species and of the order aggregation of PPy. However, it depends inversely on the proportion of the imine-like nitrogen defect (=N-). An environmental scanning electron microscope and an X-ray diffractometer, for instances, were used to investigate the interaction between PPy and acetone molecules. The swelling or the disordering effect, the hydrogen-bonding formation, and the reduction of charge carrier species are suggested to be the mechanisms causing the PPy conductivity changes when exposed to acetone vapor. (C) 2003 Elsevier Science B.V. All rights reserved.