Three-dimensional (3D) soft structures that are capable of reversible shape changes upon exposure to external stimuli (e.g., light, temperature, humidity, pH, electrical, and magnetic fields) are promising for a wide range of applications, such as soft robotics, minimally invasive medicine, and micromachines. Strategies for forming such structures usually rely on the use of stimuli-responsive materials, including hydrogels, shape memory polymers, dielectric elastomers, magnetically responsive composites, liquid crystal elastomers (LCEs), and a heterogeneous combination of these materials. Recently, LCEs, a class of stimuli-responsive materials that combine the rubber elasticity of polymer networks with the orientational order of liquid crystals (LCs) have attracted much attention due to their unique properties, including soft elasticity and large, reversible shape changes in response to a stimulus (e.g., heat or light).&nbsp;In this talk, I will discuss our recent effort in developing a facile and versatile strategy to create reconfigurable, freestanding 3D mesostructures of LCEs and magnetic LCE composites that are inaccessible with existing techniques via spatially programming LC molecules for applications including soft grippers and robots. The approach exploits compressive forces induced via the release of a biaxially prestrained substrate for deterministic geometric transformation of 2D LCE patterns into 3D structures. The resulting inhomogeneous and anisotropic spatial strain distribution causes the mechanical alignment of LC molecules into locally controlled monodomains, which are “locked” by subsequent photopolymerization. Heating and cooling across the isotropic clearing temperature of LCEs induces the nematic–isotropic transition at the local monodomains and drives the shape change of the entire LCE structure. Highly integrated experimental and computational studies of large, reversible shape-morphing behaviors of more than 20 3D mesostructures of LCEs and ferromagnetic LCE composites illustrate the reliability of the proposed strategy. Furthermore, our assembled LCE gripper demonstrates the capability of grabbing/releasing objects of diverse material compositions and geometries and up to 20 times as heavy as their own weight. We also present a reconfigurable 3D “bug” robot fabricated from ferromagnetic LCE composites, which simultaneously responds to magnetic forces and thermal stimuli for a series of biomimetic behaviors including jumping, rolling across an obstacle, crawling through a narrow crack, and delivering a cargo. Such demonstrations present potential applications of reconfigurable 3D LCE mesostructures in soft robotics, drug delivery, and many others.In addition to soft robots based on liquid crystal elastomers and their ferromagnetic composites, I will also briefly discuss our effort in developing origami-inspired soft robots and systems composed of magnetic composites.

Reconfigurable 3d Structures of Spatially Programmed Liquid Crystal Elastomers and Their Ferromagnetic Composites

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.