Electrochemo-poromechanics of ionic polymer metal composites: Identification of the model parameters

We propose a procedure to identify the parameters of a model for the multiphysics response of ionic polymer metal composites (IPMCs). Aiming at computational efficiency and accuracy, the procedure combines analytical structural mechanics and fully-coupled electrochemo-poromechanics, additionally resorting to an evolutionary algorithm. Specifically, we consider the finite-deformation electrochemo-poromechanical theory recently developed by our group, which couples the linear momentum balance, the mass balances of solvent and mobile ions, and the Gauss law. Remarkably, the theory constitutively accounts for the cross-diffusion of solvent and mobile ions. This, in conjunction with a generalized finite element implementation that we have recently proposed, allows us to accurately capture the boundary layers of ions and solvent concentrations occurring at the membrane-electrode interfaces, which govern the IPMC behaviour in actuation and short-circuit sensing. Thus, we can explore the IPMC behaviour under external actions consistent with applications and obtain accurate predictions with a reasonable computational cost for wide ranges of model parameters. We focus on experimental data from the literature that are concerned with Nafion-Pt IPMCs of variable membrane thickness and subjected to peak voltage drop across the electrodes ranging from 2 to 3.5 V (under alternating current). Importantly, the considered tests deal with both the tip displacement of cantilever IPMCs and the blocking force of propped-cantilever IPMCs. Overall, the adopted theory and the proposed procedure allow unprecedented agreement between predictions and experimental data, thus marking a step forward in the IPMC characterisation.