COMBINED ELECTROCHEMICAL AND QUARTZ CRYSTAL MICROBALANCE STUDY ON THE TEMPERATURE-DEPENDENCE OF ION AND SOLVENT SORPTION IN ELECTROACTIVE POLYMER-FILMS ON ELECTRODES

The electrochemical quartz crystal microbalance (EQCM) technique has been applied to monitor the changes of ion and solvent content within poly(tetracyanoquinodimethane) (PTCNQ) films as a function of the redox state at different temperatures. The effect of concentration of the LiCl supporting electrolyte was also studied. It was observed that the mass of the neutral film increased as the temperature was increased corresponding to a greater swelling of the surface film. The electroactivity of the film (the total charge consumed during the electrochemical transformation of the redox groups of the film) and the mass change increased simultaneously with the temperature. This is consistent with the model that with increasing temperature, the polymer film adopts a less compact structure and the diffusion of the counter-ions as well as segmental motion of the polymer chain becomes less hindered. It was established that in the mass changes accompanying the redox processes occurring in PTCNQ films, the solvent sorption is predominant and the incorporation of ions plays a lesser role. The extent of the swelling depends on the concentration of the bulk electrolyte solution due to the decrease in water activity and the diminishing number of available water molecules for the hydration of Li+ ions. In contact with electrolyte solutions of low or medium concentration, the films are highly swollen at elevated temperatures and consequently an interplay between a rigid layer and viscous behaviour can be observed.