Conducting polymer actuators

Abstract

Conducting polymers are unusual organic materials featuring high electronic conductivity. Recently it has been observed that some of these polymers change in dimension when their oxidation state is altered. Dimensional changes induced by electrochemical activation in the conducting polymer polypyrrole are investigated. Swept sine and step voltage and current inputs are employed to investigate the nature of this electro-mechanical coupling. Strains of up to 6 %, strain rates of 4 %/s, power to mass ratios of 40 W/kg and forces of up to 34 MN/m2 are achieved. Polypyrrole nearly equals mammalian skeletal muscle in power to mass and exceeds it in force by two orders of magnitude. A model is developed which predicts the electrochemical impedance, and relates electrical input to mechanical output. Observations and modeling indicate that diffusion and capacitive charging limit strain rate. The use of thinner films is predicted to increase strain rate and power to mass ratios by at least two orders of magnitude. Initial applications are likely to be in microelectromechanical systems.