Ionic polymer-metal composites (IPMCs) are smart materi-als which function as soft sensors and actuators. When a small DC voltage (1-5 V) is applied to an IPMC in a cantilever con figuration, ion and solvent transport through the thickness of the polymer membrane causes the transducer to bend towards the anode. For device development and use in engineering applica-tions, actuation is often described at a higher level in terms of an electromechanical coupling between the ionic charge distri bution and the stresses developed in the IPMC. In this work we derive a set of relationships describing the coupling response by starting with basic considerations of polymer microstructure and local interactions during actuation. A micromechanical model-ing framework is employed in order to account for the material microstructure. Using a generalized expression for electrostatic cluster pressure which takes into account clusters recombining to from larger cluster upon expansion, we define an effective local stiffness which varies with both solvent uptake and charge den-sity in the boundary layers. An equilibrium relationship between solvent uptake and charge density is determined by considering the free energy of the homogenized polymer as the sum of elas-tic, electrostatic, and chemical components. Stress developed in the boundary layers is then calculated from changes in local stiffness and solvent uptake with respect to charge density. The resuiting relationship for electromechanical coupling is found to be in good agreement with previous empirical models, thus serv-ing as a model validation and demonstrating why certain forms for electromechanical coupling can be used to explain a varietyof experimental observations. Specifically, we see that stress de veloped in the boundary layers is well described as a quadratic polynomial in charge density due to the form of the electrostatic cluster pressures.
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