Optimization of active electrodes for novel ionomer-based ionic polymer transducers

This study expands the number of novel synthetic ionomers specifically designed for performance as ionic polymer transducers (IPT) membranes, specifically employing a highly branched sulfonated polysulfone. Control of the synthetic design, characterization, and application of the novel ionomer is intended to allow fundamental study of the effect of polymer branching on electromechanical transduction in IPTs. Fabrication methods were developed based upon the direct application process (DAP) to construct a series of stand-alone electrodes as well as full IPTs with corresponding electrode compositions. Specifically, the volumetric ratio of RuO₂ conducting particles to the novel ionomeric matrix was varied from 0 - 45 vol % in the electrodes. Electrical impedance spectroscopy was employed to determine the electrical properties and their variation with electrode composition separate from and in the IPT. A percolation threshold was detected for increased ionic conductivity of the stand-alone electrodes and the full IPTs based on increased loading of conducting particles in the electrodes. An equivalent electrical circuit model was applied to fit the impedance data and implicated interfacial and bulk effects contributing differently to the electrical properties of the electrodes and IPT as a whole. The fabricated IPT series was further tested for bending actuation in response to applied step voltages and represents the first demonstration of IPTs constructed with the DAP process using 100 % novel ionomer in all components. The percolation behavior extended to the bending actuation responses for strain and voltage-normalized strain rate and is useful in optimizing IPT components for maximum performance regardless of the ionomer employed.