A Dynamic Electromechanical Model for Electrochemically Driven Conducting Polymer Actuators

In this paper, an analytical model is presented to predict the actuation response of electrochemically driven structures. A 2-D impedance model is first presented that uses a conducting polymer RC transmission line equivalent circuit to predict the charge transfer during actuation. The predicted electrochemical charging is then coupled to a mechanical model to find the actuation response of a bending structure. The advantage of this model compared to existing models is that it represents the 2-D charging of the polymer, namely through the thickness of the polymer structure and along its length. The model considers both ion "diffusion" through the thickness and electronic resistance along the length. The output of the impedance model is charge density in the polymer as a function of position and time, which is then used to estimate free strain via the strain to charge ratio. Given the modulus of the polymer and of passively deformed structures, time-dependent deformation is then determined. The complete electromechanical model is a function of ionic and electronic conductivities, dimensions, volumetric capacitance, elastic modulus, and strain to charge ratio, all of which are measured independently. The full electromechanical model is shown to provide a good description of the response of bending polymer structures when comparing with experimental results. The model can be effectively used as a design tool for electrochemically driven devices.