PAPER CANCELLED - Advances of Thermoplastic Elastomer Systems As Electroresponsive Media

Electroactive polymer (EAP) actuators and generators constitute an exciting technology platform that has attracted tremendous interest in the academic and commercial communities. Still, for many proposed applications in the biomedical and robotics industries, EAPs have not made the transition to industrially relevant technologies. Using thermoplastic elastomer gel (TPEG) systems as physically tunable soft materials for this purpose, we hope to improve performance and expedite the transition of EAPs to a marketable technology.

In this work, we focus on a class of EAP actuators commonly referred to as dielectric elastomers (DEs). A dielectric elastomer is essentially a soft capacitor in which the dielectric layer is compliant such that electrostatic attractive forces across the capacitor are substantially large to cause isochoric compression. The use of TPEGs in such constructs is particularly interesting because of their large actuation strains (≈ 300%), high electromechanical coupling efficiencies (> 90%), low strain-cycling hysteresis, and quick electromechanical response. There are, however, several important drawbacks to DEs that limit their commercial use: an exceedingly high electric field (~10-100 kV/mm) is frequently necessary to induce electroactuation, and the requirement of ultra-soft elastomers for substantial actuation limits the work capacity and energy density.

The use of TPEGs composed of selectively-solvated multiblock copolymers as DEs affords significant mechanical and chemical tunability. We have previously demonstrated the use of low-polarity solvents as a means by which to achieve mechanical tunability in such materials. By judicious selection of the chemical identity of the blocks comprising the TPE and the corresponding selective solvent, we can design DEs that reduce operating voltage and achieve high strains. This has been previously established for styrenic TPEs, and now we extend this design paradigm to olefinic TPEs as well. The energy density can be improved by increasing the electric permittivity through the addition of high-polarity elastomers and solvents to improve the electromechanical performance of DEs.