SHORT-RANGE ELECTRON-ION INTERACTION EFFECTS IN CHARGING THE ELECTROACTIVE POLYMER-FILMS

This paper has analyzed the effects of the polymer/solution interfacia l potential as a function of electrode polarization as well as of vari ous short-range interactions between the charged components of the pol ymer phase, electronic and ionic species. Charging/discharging process es depend crucially on whether the value of interaction parameter is g reater (repulsion or weak attraction between the species) or less (suf ficiently strong attraction) than its critical value. In the former ca se it can be realized as a ''continuous'' transition between the insul ative and conductive states of the film at sweeping polarization, the difference between the him charging and discharging (''hysteresis'') b eing solely due to conventional relaxation processes (diffusion, slow interfacial transfer etc). Anodic and cathodic current peaks are gener ally non-symmetrical, due to the film/solution potential variation. In the latter case, two quasi-equilibrium states, low- and high-density ones, coexist within a polarization range separated by a free-energy b arrier so that the charging/discharging process has features of a phas e transition. It may lead to a considerable hysteresis during the cycl ing process, even if it is realized in a quasi-equilibrium way. Variab le behaviour has been found for the partial interfacial potentials ver sus electrode polarization, phi(m/p)(E) and phi(p/s)(E), depending on individual charges of electronic and ionic species, on the value of th e global interaction parameter as well as on the ratio of different co ntributions to the free energy, due to electron-electron, electron-ion and ion-ion short-range interactions. These curves may be of an S- or Z-shape, possess extrema or even a loop with the self-crossing point. Highly narrow peaks are characteristic of these systems with a strong attraction between the species. There is again an asymmetry between t he anodic and cathodic peaks as well as with respect to peak potential s, due to the film/solution potential variation. The ratio of anodic a nd cathodic peak widths depends, on the particular type of the rate-de termining process, eg slow electron or ion interfacial transfer or ''d roplets'' formation.