Photo-Dynamic Elastomer Networks for Actuator Applications

Abstract

Dielectric elastomer actuators are a class of smart electroactive polymers capable of generating large strains under an applied electric field. Selectively tailoring polymer network compositions can optimize the rheological, mechanical, and electrical properties of dielectric elastomers. Thiol-ene based siloxane crosslinked elastomers were formulated by tuning the functionality, molecular weight, and stoichiometry of constituent oligomers. UV polymerization expedited the reaction and curing rates to produce soft elastomers with enhanced actuation performance. In-situ photo-rheology was used to characterize various siloxane networks. New dynamic photo-tunable properties were discovered at an off-stoichiometric thiol to vinyl ratio for thiol-ene elastomers. Different degrees of dynamic switching were attainable based on the molecular weight of polymer chains, the degree of functionalization, the ratio of thiol to alkene content, and the type and concentration of photo-initiators. These photo-induced covalent adaptive networks (photo-CANs) demonstrated reversible sol-gel transition, fast and low energy stress relaxation, and on-demand photo-plasticity at ambient temperatures leading to applications ranging from damage recovery and healing, repatterning and remolding, to light-induced reversible adhesives. Furthermore, the dynamic photo-CANs retained good dielectric properties under application of high electric field. New actuators, photo-capacitors (photo-CAPs), with the ability to withstand voltage and light simultaneously, were designed and fabricated in a bilayer spring system where a standard elastomer was used as a parallel spring to restore the shape of the photo-plastic elastomer. While not perfectly reversible, it is the first demonstration of its kind opening up new opportunities in the field of multi-stimuli responsive soft actuators.