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 species in conducting polymers is presented. It takes into account the diffusion of anions, cations and solvent in the polymer and the ion and solvent transfer kinetics at the polymer | solution interface. The electrochemical impedance and electrogravimetric transfer function are derived and are calculated and plotted under several experimental conditions. Simultaneous measurements of the electrochemical impedance and of the electrogravimetric transfer function were carried out on polyaniline films coating one of the electrodes of a quartz crystal microbalance. The insertion or expulsion of anions, cations and solvent was demonstrated through anion/solvent and cation/solvent partial electrogravimetric transfer functions for this polymer. The derivative of the isotherm of insertion or expulsion of ions and solvent was evaluated in the whole active potential range. Various experimental conditions (film thickness, anions) were tested.