Irregular Response of the Polypyrrole Films to H2S

The immobilization of surfactant anions (e.g., dodecylsulfate, DS) in PPy films leads to stable, well conducting polymer films, and the film shows sensitivity to several kinds of gases and vapors. According to the generally accepted interpretation in the literature, the pattern of the interaction between the films and gases basically depends on the electron donor or acceptor behavior of gases. This concept proved to be a suitable explanation in case of NH3, where both the spectra and the conductance changed as upon a partial electrochemical reduction. However, we observed discrepancy, when PPy/DS films were exposed to H2S. Upon exposure of the film to H2S the conductance has increased significantly, although UV-vis spectra changed according to a reductive effect. The effect of different vapors was studied by spectrophotometric, AC conductance/resistance and FTIR measuring techniques. The results are explained by the consideration of the mobility of different charge carriers, by taking proton exchange processes also into account.