Modeling shape transformations in liquid crystal elastomers
Liquid Crystal Elastomers (LCEs) undergo reversible shape change in response to any stimulus that affects the strength of nematic order: a change of temperature, illumination, chemical environment, or applied electric field. The trajectory of shape change is programmed by patterning the nematic director when the elastomer is cross-linked. These soft actuators can be fabricated as thin films, surface coatings, or 4D printed solids and have potential applications in soft robotics, biomedical devices, microfluidics, and sensors. We review recent advances in methods for director patterning of LCE devices and other novel methods for shape programming and actuation.
Next we investigate shape transformations in LCEs with topological defects, using nonlinear finite element method (FEM) simulation and analytical calculations. We model LCE coatings on a rigid substrate, with director field containing patterned topological defects oriented either parallel or perpendicular to the surface normal. These drive shape transformations of initially flat films to form surface microchannels, spikes, or dimples. We also model shape transformations in 4D printed structures. Results are compared with relevant experiments.
Our results demonstrate that actuation geometry produced by a disclination in an LCE coating is controlled not only by topological charge/orientation but also by defect core structure. Using FEM simulations, we explore one defect structure that produces biomimetic “octopus-like” suckers, which might be used to grasp and release nonporous objects on command. Such a device would have the potential to achieve strong, reversible adhesion to both wet and dry surfaces. We discuss possible applications in soft robotics and biomedical devices.