Shape changes in chemoresponsive liquid crystal elastomers

Liquid crystal elastomers are ordered polymers that undergo reversible, anisotropic shape change in response to a number of stimuli, including heat, light, and solvent. In this study, we design liquid crystal elastomers that actuate both axially and torsionally in response to chemical stimuli. We characterize the response of uniaxially-aligned liquid crystal elastomer films exposed to a variety of chemical stimuli of varying quality. In each solvent, there is a contraction along the alignment direction paired with an expansion in the perpendicular directions. Torsional actuation is generated by patterning a twisted alignment through the thickness of the liquid crystal elastomer. These hierarchically-patterned materials reversibly transition from flat to helical with over 200 degrees/mm of twist in chemical vapor. This response is stable for at least 100 cycles. Ultimately, this chemoresponse is combined with mechanical instability to make high-twist torsional actuators with peak velocities of almost 400 RPM. (C) 2016 Elsevier B.V. All rights reserved.