Modeling and characterization of ionic polymer transducers for sensing and actuation

Ionic polymer transducers comprise a class of active material that exhibit interesting chemoelectromechanical coupling capabilities. With the ability to convert energy between chemical, electrical and mechanical domains, these materials offer potential for use in numerous engineering applications. The research presented in this dissertation focuses primarily on the electromechanical coupling that exists within these ionic polymer materials. When plated with a conductive surface electrode, these ionomeric membranes function effectively as either sensors or actuators. Mechanically compliant, these transducers demonstrate large strain, but limited force, capabilites while operating at low excitation voltages.

The objective of this research is to improve understanding of the transduction properties inherent in the ionic polymer. Most of the existing work in this area has focused on the actuation response, therefore the focus of this research is on providing a better understanding of the sensing and impedance responses of the ionic polymer transducer. Using transport theory as the basis, a set of analytical models are developed to characterize the charge motion that develops within an ionomer when subject to either mechanical or electrical loading. These models characterize the internal potential and charge density responses of the membrane, as well as the expected surface current that would be measured as the result of external loading.

In addition to the analytical work, numerous experimental characterizations of the membrane are also presented. The ionic polymer's actuation, sensing and impedance responses are each considered as a function of the counterion and solvent type present within the ionic polymer. These studies demonstrate the importance of the ionomer's impedance response in understanding the electromechanical capabilites of an ionic polymer transducer. Most sample-to-sample variation can be attributed to the voltage to current conversion that occurs within the ionic polymer. By relating these experimental results to the analytical models, it is possible to characterize these changes in performance in terms of the effective diffusion and permittivity parameters of the transducer. A final series of experiments are also considered to determine the effectiveness of the model in predicting the impedance response as a function of temperature, solvent viscosity and preloading of the membrane.