Interpenetrating polymer network (IPN) as tool for tuning electromechanical properties of electrochemical actuator operating in open-air

Electrochemical actuators operating in open-air are trilayer electrochemical devices based on an ionically conducting membrane sandwiched between two electrodes of electronic conducting polymers (ECP). Tuning functional properties of the actuator, i.e. the output force, is demonstrated via the modification of the ECP's surrounding macromolecular architecture. Theoretical models have suggested that the output force of trilayer actuators is related to the Young's modulus of the electrodes. As a consequence, we designed Interpenetrating Polymer Network (IPN) membranes combining three different polymer networks with a co-continuous morphology to act as a host matrix for ECP electrodes. Each of these polymer networks is chosen for a specific role: (i) poly(ethylene oxide) network providing ionic transport medium within the ECP electrodes, (ii) Nitrile Butadiene Rubber providing endurance, flexibility and robustness to the final device and (iii) polystyrene to increase the Young's modulus of the ECP electrodes. The synthesized IPNs have been thoroughly characterized. The performances of resulting actuators have been assessed. The output force is almost doubled due to the stiffening effect of the polystyrene phase, as predicted by the beam theory.