Solvent and salt transfer upon redox switching of electroactive polymers

A thermodynamic analysis of mobile species transfer accompanying redox switching of electroactive polymer films is presented. Population changes of counterion, solvent, and co-ion (salt) are considered. Counterion population changes are dictated solely by electroneutrality (charge injection). Solvent and salt population changes are also dictated by activity constraints (polymer chemistry) and thus may be in either direction. The extent of solvent transfer accompanying redox switching of an electroactive polymer film is constant over a wide range of bathing solution compositions. Only counterion and solvent will transfer under permselective conditions. Under nonpermselective conditions the salt also transfers. For a film immersed in a solution of a single electrolyte, a procedure is given for extracting the concentration-dependent contributions of individual mobile species transfers. In the context of the electrochemical quartz crystal microbalance technique, the thermodynamic analysis allows separation of the overall film mass change into counterion, solvent, and salt contributions.