Ions and solvent transport across conducting polymers investigated by ac electrogravimetry. Application to polyaniline

A simplified model of the transport of the charge carriers and neutral spec ies in conducting polymers is presented. It takes into account the diffusio n of anions, cations and solvent in the polymer and the ion and solvent tra nsfer kinetics at the polymer/solution interface. The electrochemical imped ance and electrogravimetric transfer function are derived and are calculate d and plotted under several experimental conditions. Simultaneous measureme nts of the electrochemical impedance and of the electrogravimetric transfer function were carried out on polyaniline films coating one of the electrod es of a quartz crystal microbalance. The insertion or expulsion of anions, cations and solvent was demonstrated through anion/solvent and cation/solve nt partial electrogravimetric transfer functions for this polymer. The deri vative of the isotherm of insertion or expulsion of ions and solvent was ev aluated in the whole active potential range. Various experimental condition s (film thickness, anions) were tested. (C) 2000 Elsevier Science S.A. All rights reserved.