TRANSIENT EFFECTS IN THE INTERACTION BETWEEN POLYPYRROLE AND METHANOL VAPOR

A quantitative study of the room temperature transient behavior of polypyrrole thin films containing tosylate and tetrafluoroborate anions exposed to methanol vapor was carried out. Both films had the same doping level. Changes of mass, work function, and optical absorbance were recorded simultaneously. A Langmuir-type isotherm fits adequately the experimental data. The dependence of the equilibrium vapor uptake on the polymer film thickness proves that a bulk absorption occurs. The linear dependence of the change in work function on the concentration of molecules present in the film indicates that a weak charge-transfer interaction is taking place. We demonstrate that the sorption is the driving force of the interaction which is affected by the nature of the counteranion incorporated in the polymer matrix. As a result, the rate constants of the mass transients for the absorption and desorption processes are found to increase with the amount of vapor in the film. Owing to the weak interaction between the small sized vapor molecules and the network solid, the diffusion occurs instantly so that the adsorption appears to be the rate-limiting process.