Modelling mobile species population changes in electroactive films under thermodynamically and kinetically controlled conditions

Abstract

We describe a new model for electroactive film mobile species (ion and solvent) populations under a range of thermodynamically and kinetically controlled conditions, that allows the film state to be visualized in 3D E, Q, Λ-space, where Λ represents film composition. Under thermodynamically controlled conditions, when film composition is a single-valued function of potential, the model allows one to calculate and represent solvent content as a function of redox state under both ideal and non-ideal conditions. Curvature in the solvent population-charge relationship can result from either thermodynamic or kinetic factors. Under kinetically controlled conditions (with no transport limitations) the model can describe slow electrochemical and solvation processes, both in the absence and presence of non-ideal solvation thermodynamics. The film compositional signature in E, Q, Λ-space allows visual diagnosis of thermodynamic versus kinetic control and the identification of various possible phenomena; these include film reconfiguration, ion and solvent trapping, relative rates of ion versus solvent transfer, and relative rates of solvent entry versus exit. Application of the model is demonstrated for the case of polyvinylferrocene films exposed to aqueous media under permselective conditions.