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Fast liquid crystal elastomer swims into the dark

Peter Palffy-Muhoray ,Miguel Camacho-Lopez ,Heino Finkelmann ²,Michael Shelley ³
Liquid Crystal Institute, Kent State University School of Physics and Astronomy, University of St. Andrews, Scotland ²Institute fur Macromoleculare Chemie, Albert-Ludwigs Universitat, Germany ³Courant Institute of Mathematical Sciences, New York University
Liquid crystal elastomers (LCEs) are rubbers whose constituent molecules are orientationally ordered. Their salient feature is strong coupling between orientational order and mechanical strain. Stretching or otherwise deforming an LCE sample changes the orientational order, which in turn changes bulk properties such as birefringence and dielectric susceptibility. Conversely, changing the orientational order gives rise to internal stress, which leads to strains that can change the shape of a sample. While orientational order can be affected by changes in temperature and other externally applied fields, light can also change the orientational order via a number of distinct processes. We demonstrate here that by dissolving azo dyes in an LCE sample, its mechanical deformation in response to visible light becomes large and very fast. Light induced bending of more than 60 degrees has been observed on the timescale of tens of milliseconds; this is more than two orders of magnitude faster than previous results. Rapid light induced deformations allow LCE materials to interact with their environment in new and unexpected ways. We report here also the astonishing observation that when light is shined from above on a dye-doped LCE sample floating on water, the LCE “swims” away from the light.

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