High-Strain ionomeric-ionic liquid composites via electrode tailoring

Abstract

Ionomeric polymers are a class of electromechanical transducer consisting of an ionomeric substrate with metal-plated electrodes. Application of a low voltage (< 5 V) across the thickness of the membrane produces controllable strain. The advantage of ionomeric polymers compared to other types of electromechanical transducers (e.g. piezoelectric polymers) is low-voltage operation, high strain capability, and high sensitivity in charge mode. Two of the primary limitations of ionomeric polymers for electromechanical transducers are unstable operation in air and solvent breakdown at low voltage. This work focuses on overcoming these limitations through the development of an ionic liquid-ionomeric composite with a tailored electrode composition that maximizes strain output. It is becoming clear that charge accumulation at the polymer-electrode interface is the key to producing high strain in ionomeric polymer transducers. In this work we combine a previously developed process for incorporating ionic liquids into ionomer membranes with a new method for tailoring the electrode composition. The electrode composition is studied as a function of the surface-to-volume ratio and conductivity of the metal particulates. Results demonstrate that the surface-to-volume ratio of the metal particulate is critical to increasing the capacitance of the transducer. Increased conductivity of the metal particulates produces improved response at higher frequencies (> 10 Hz) but this effect is small compared to the increase in strain produced by maximizing the capacitance. Increasing capacitance produces a transducer that is able to achieve > 2% strain at voltage levels of +/- 3 V.