Effects of electrode morphology on the performance of BPSH and PATS ionic polymer transducers

Abstract

Ionic polymer transducers are soft actuators that produce large bending deflections when a small voltage is applied across their thickness. The electromechanical coupling in ionomeric materials is due to the charge motion in the polymer backbone. Increasing the capacitance of the actuator increases the motion of the charges and the actuation performance of ionic polymer transducers has been shown to be strongly correlated with charge motion. Ionomers exhibit large capacitance due to the electric double layer formed on the polymer-electrode interface. Increasing the effective interfacial area results in the increase in the capacitance, and manipulating the electroding process of the ionic polymers has proved to have major effect on capacitance and therefore transduction. In this paper a novel electroding technique is developed and characterized. The method is composed of mixing an ionic polymer solution with a fine metal powder such as RuO_2, and attaching it to the membrane as an electrode. Scanning Electron Microscopy images are obtained for several plating processes, and relations between plating parameters and electrode morphology are established. The transducers are characterized as actuators by measuring their strain output, force output, and capacitance. Capacitance values of up to 45 mF/cm^2 are obtained using the novel electroding method, which is between five and ten times higher than that obtained with a standard impregnation-reduction process. The performance of the transducers fabricated with the novel electroding technique exceeds the performance of those fabricated with the impregnation-reduction method by a factor of between 2 and 5. Transducers fabricated with the impregnation-reduction method generally produce 200 to 500 microstrain/V while the ones fabricated with the new process exhibited free strain values of greater than 1550 microstrain/V at low frequencies.