Conducting polymer artificial muscles

Abstract

The application of conducting polymers for the direct conversion of electrical energy to mechanical energy in electromechanical actuators is analyzed using theoretical and experimental results. Basic principles of operation, predicted performance advantages and disadvantages, comparisons with natural muscle, evaluations of initial device demonstrations, and methods for improving device performance are provided. The very high predicted work densities per cycle, force generation capabilities, and power densities provide major advantages compared with piezoelectric polymers – as do the low operation voltages. These advantages are countered by cycle life and energy conversion efficiency limitations, as well as the need to use microelectrodes in order to achieve very high rates. Hydrostatic devices and extensional devices that provide either in-phase or out-of-phase electrode deformations are considered. Special types of conducting polymer actuators are also proposed, including photo-powered, chemically powered and self-powered actuators, which provide novel methods for assembling complex microstructures. Novel methods are described for actuator fabrication, such as ‘redox poling’, wherein anode, cathode and separating electrolyte layers are generated from a film in a single redox step. New actuator compositions are also proposed for obtaining improved performance, such as conjugated carbon phases having conjugation in either two or three dimensions. Finally, conducting polymer actuators based on double-layer charging are proposed which are predicted to provide increased energy efficiency and cycle life compared with the faradaic actuators.