Redox level-dependent impedance model for conjugated polymer actuators

The reduction–oxidation (redox) level of a conjugated polymer has significant impact on its electro-chemo-mechanical properties, such as conductivity, impedance, and Young’s modulus. Understanding and modeling the influence of redox level is of interest to both fundamental understanding of conjugated polymers and practical applications of these materials. In this paper a redox level-dependent impedance model is developed by incorporating dynamics of ionic diffusion, ionic migration, and redox reaction. The model, in the form of a transfer function, is derived through perturbation analysis around a given redox level, and extends the diffusive-elastic-metal model proposed by J. Madden. Experimental measurements under various redox conditions, achieved through applying different DC bias voltages, correlate well with the model prediction and thus validate the proposed model. This work, for the first time, incorporates the effect of redox level into the dynamics of conjugated polymers in an integrative way, and facilitates further analysis and control of these materials using nonlinear control tools.