Modeling Defects, shape evolution, and Programmed auto-Origami in liquid crystal elastomers

Liquid crystal elastomers represent a novel class of programmable shape-transforming materials whose shape-change trajectory is encoded in the materials nematic director field. Using three-dimensional non-linear finite element elastodynamics simulation, we model a variety of different actuation geometries and device designs: thin films containing topological defects, patterns that induce formation of folds and twists, and a bas-relief structure. The inclusion of finite bending energy in the simulation model reveals features of actuation trajectory that may be absent when bending energy is neglected. We examine geometries with a director pattern uniform through the film thickness encoding multiple regions of positive Gaussian curvature. Simulations indicate that heating such a system uniformly produces a disordered state with curved regions emerging randomly in both directions due to the films up/down symmetry. In contrast, applying a thermal gradient by heating the material first on one side breaks up/down symmetry and results in a deterministic trajectory, producing a more ordered final shape. We demonstrate that a folding zone design containing cut-out areas accommodates transverse displacements without warping or buckling, and demonstrate that bas-relief and more complex bent/twisted structures can be assembled by combining simple design motifs.