Solvation-Driven Actuation of Anion-Exchange Membranes

Ion-exchange membranes, conventionally utilized in separation processes of electrolyte solutions, are electroactive polymers that display a unique coupling between electrochemistry and mechanics. Previous experimental studies have demonstrated the possibility of actuating cation-exchange membranes in salt solution through the application of a remote external electric field. The use of anion-exchange membranes as contactless actuators, however, has never been documented and little is known about the physics of their actuation. Here, it is reported for the first time the possibility of contactless actuating anion-exchange membranes in salt solutions; such an actuation is mediated by the selection of anions in the external salt solution and the membrane. Actuation is attributed to the physical phenomenon of solvation, the interaction between ions and solvent in solution. Contrary to previous studies with cation-exchange membranes, the results show that anion-exchange membranes consistently bend toward the anode. The integration of anion-exchange and cation-exchange membranes in composites promises innovative programmable contactless actuators, with applications in underwater robotics and biomedical engineering.