Multiple shapes from a single nematic elastomer sheet activated via patterned illumination

Abstract

Liquid crystal elastomers (LCEs) undergo a large uniaxial contraction upon thermal or optical stimulation. LCE sheets are often fabricated with a spatially patterned direction of contraction, which can sculpt the sheet into a Gauss-curved surface. Here, we instead consider LCE sheets subject to patterned stimulation intensity, leading to a control of contraction strength. We show such patterns may similarly sculpt a complex surface, but with the advantage that arbitrarily many surfaces may be achieved sequentially in the same sample, thus breaking the link between microstructure and shape adaptivity. We first consider a monodomain LCE in which some regions are actuated and others are not. We discuss how to join actuated and unactuated regions compatibly, and use this design rule to generate patterns for cones, anti-cones, arrays of cones, and a wine-bottle. We validate the patterns numerically via elastic shell simulations and demonstrate them experimentally via patterned photo-chemical actuation. Secondly, we consider an LCE disk with an azimuthal director profile actuated by a radially varying stimulus. We show, theoretically and numerically, how to design a stimulation profile to sculpt any surface of revolution. Such reconfigurable actuation offers enticing possibilities for haptics, robotics and locomotion.

Light-driven peristaltic pumping by an actuating splay-bend strip

“…However, Gauss’s theorema egregium dictates that a doubly curved 2D blister requires an in-plane variation to form, and then cannot be defeated without energetically costly stretch. Such variation can be achieved via patterns of alignment 53 , or patterns of actuation strength 31 , 54 , but do require geometrically large strains that are only achievable with LCEs. As an example of the power of such metric-mechanics , LCE sheets programmed to rise into cones on heating/illumination 55 are capable of lifting thousands of times their own weight 56 .…”