Abstract
Ionic Polymer Metal Composites (IPMCs) consist of two noble metal electrodes plating an electroactive polymeric membrane, referred to as ionomer, which is electroneutralised by a solvent including mobile ions. The IPMC manufacturing leads to thin interphase regions next to the electrodes, the so-called Composite Layers (CLs), in which metal atoms occupy interstitial sites within the ionomer. In this work we extend previous efforts of our group on IPMC compression sensing to include the important effect of CLs, where large variations of the electrochemical properties occur. In IPMC compression sensing the application of a through-the-thickness displacement leads to a shortcircuit electric response, here assumed to be governed by a linearised <i>modified</i> Poisson-Nernst-Planck (PNP) system of partial differential equations (PDEs), to be solved for the time-evolving electric potential and mobile ions concentration as functions of the displacement field evaluated through the linear momentum balance. The variation of material properties in the CLs requires the simultaneous integration of the governing system of PDEs in three regions: the membrane and the two CLs. To this purpose, we resort to the perturbative method of matched asymptotic expansions. Except for a numerical inverse Laplace transform, this allows us to obtain an analytical solution through which we establish an equivalent circuit model elucidating the main features of the IPMC sensing behaviour. We validate and discuss the analytical solution through comparison with finite element analyses, whereby we also numerically solve the nonlinear modified PNP systems fully coupled with the linear momentum balance accounting for the electrochemical stresses. We finally provide some insight into the role of CLs in the IPMC sensing behaviour, by assessing its sensitivity to some key parameters. We expect the obtained results to aid the design of optimised IPMC sensors.
Highlights
Ionic Polymer Metal Composites (IPMCs) are transducers whose electroactive behaviour is guaranteed by an electrically charged ionomeric membrane infused with a solvent containing mobile ions
In IPMC compression sensing the application of a through-the-thickness displacement leads to a shortcircuit electric response, here assumed to be governed by a linearised modified Poisson-Nernst-Planck (PNP) system of partial differential equations (PDEs), to be solved for the time-evolving electric potential and mobile ions concentration as functions of the displacement field evaluated through the linear momentum balance
We have presented in detail the analytical solution for the short-circuit electric response of Ionic Polymer Metal Composites (IPMCs) subjected to a through-the-thickness displacement
Summary
Ionic Polymer Metal Composites (IPMCs) are transducers whose electroactive behaviour is guaranteed by an electrically charged ionomeric membrane infused with a solvent containing mobile ions. To describe the IPMC behaviour, in this investigation we adopt the Cha and Porfiri [4] electrochemomechanical theory In this theory, the counterions motion governs both sensing and actuation through ions accumulation or depletion in the proximity of the ionomer-electrode interfaces, forming the so-called boundary layers. In the proximity of the ionomer-electrode interfaces, the presence of metal particles among the ionomer macromolecules modifies the stiffness of the membrane, but primarily its electrochemical properties, leading to an increased electric permittivity along with a decreased counterions diffusivity In literature, these interphase regions are referred to as either intermediate layers [15] or Composite Layers (CLs) [16, 17].
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