Thermally Driven Giant Bending of Liquid Crystal Elastomer Films with Hybrid Alignment

Abstract

We have investigated the thermally induced bending deformation of nematic elastomers with hybrid alignment (HNEs) where the director continuously rotates by 90° (from planar alignment to vertical alignment) between the top and bottom surfaces. The flat specimen of nematic gel in the preparation state exhibits a considerable bending when allowed to deswell to the dry state. The curvature of the dried elastomer film markedly depends on temperature. The curvature in the nematic state increases with heating, and the film apparently becomes flat at a certain temperature. Further heating induces the bending in the opposite direction. In the high-temperature isotropic state, the curvature is independent of temperature. This bending deformation is thermally reversible. We successfully interpret the temperature dependence of curvature for the HNEs assuming a linear variation of strain in the thickness direction on the basis of the thermally uniaxial deformation of the nematic elastomers with globally planar or vertical alignment. We also conduct a numerical simulation on the basis of a nonlinear elasticity model to reproduce the observation. The simulation using the material parameters that are almost identical with the corresponding experimental values explains the phenomenon and demonstrates the stress and strain distribution in the curled HNEs.