Ionic polymer metal composites (IPMCs) consist of an electroactive polymeric membrane plated with metal electrodes. They hold promise as actuators and sensors for soft robotics and biomedical applications. Their capabilities ensue from the motion, within the membrane, of a fluid phase consisting of ions dispersed in a solvent. Toward a thorough understanding of IPMC multiphysics, we propose a large deformation theory combining electrochemistry and poromechanics. Namely, we modify the theory recently developed by Porfiri’s group by introducing the transport of the solvent, whose redistribution determines the volumetric deformation of the fluid-saturated membrane, and we further account for the cross-diffusion of solvent and ions. In actuation, the imposed voltage drop across the electrodes triggers ion migration, such that the solvent is transported toward the cathode by electro-osmosis. This determines the initial bending toward the anode; then, back-relaxation occurs because of both the solvent counter-diffusion and the asymmetric redistribution of ions near the electrodes. In short-circuit sensing, the applied load triggers solvent motion, such that ions are mainly transported toward the cathode by convection with the solvent. This determines charge accumulation; then, ion counter-diffusion leads to a decrease of the charge stored at the electrodes. We demonstrate that these behaviors can be predicted by the proposed theory on the basis of relevant finite element benchmarks. Additionally, our analysis encompasses the assessment of the role of the membrane elastic moduli in the counter-diffusion of solvent and ions in IPMC actuation and sensing.

离子聚合物金属复合材料（IPMC）由镀有金属电极的电活性聚合物膜组成。它们有望成为用于软机器人和生物医学应用的执行器和传感器。它们的能力来自膜内运动，该运动由分散在溶剂中的离子组成的液相组成。为了彻底理解IPMC的多物理场，我们提出了一种将电化学和物理力学相结合的大变形理论。即，我们通过引入溶剂的传输来修改Porfiri小组最近开发的理论，该溶剂的重新分布决定了流体饱和膜的体积变形，并进一步说明了溶剂和离子的交叉扩散。在驱动中，施加在电极两端的电压降会触发离子迁移，从而使溶剂通过电渗向阴极输送。这确定了朝阳极的初始弯曲；然后，由于溶剂反向扩散和电极附近离子的不对称重新分布，发生了背松弛。在短路检测中，施加的负载会触发溶剂运动，从而离子主要通过与溶剂对流而向阴极传输。这决定了电荷的积累；然后，离子反扩散导致电极上存储的电荷减少。我们证明了这些行为可以通过所提出的理论在相关的有限元基准的基础上进行预测。此外，我们的分析包括评估膜弹性模量在IPMC致动和传感中溶剂和离子反扩散中的作用。