Twist again: Dynamically and reversibly controllable chirality in liquid crystalline elastomer microposts

Abstract

Photoresponsive liquid crystalline elastomers (LCEs) constitute ideal actuators for soft robots because their lightinduced macroscopic shape changes can be harnessed to perform specific articulated motions. Conventional LCEs, however, do not typically exhibit complex modes of bending and twisting necessary to perform sophisticated maneuvers. Here, we model LCE microposts encompassing side-chain mesogens oriented along a magnetically programmed nematic director, and azobenzene cross-linkers, which determine the deformations of illuminated posts. On altering the nematic director orientation from vertical to horizontal, the post's bending respectively changes from light-seeking to light-avoiding. Moreover, both modeling and subsequent experiments show that with the director tilted at 45°, the initially achiral post reversibly twists into a right-or left-handed chiral structure, controlled by the angle of incident light. We exploit this photoinduced chirality to design "chimera" posts (encompassing two regions with distinct director orientations) that exhibit simultaneous bending and twisting, mimicking motions exhibited by the human musculoskeletal system.

Light Tracking and Light Guiding Fiber Arrays by Adjusting the Location of Photoresponsive Azobenzene in Liquid Crystal Networks

“…Such sunflower-like UV-lighttracking movements of fibers can be ascribed to the gradient isomerization and asymmetric shrinkage ratio through the fiber depth. [38,39]…”

A dynamically reprogrammable metasurface with self-evolving shape morphing

“…Pioneering studies rely on an exploitation of responsive materials or material configurations to create active structures that shift their shapes in response to external stimuli [34][35][36][37][38] . Smart materials (e.g., liquid crystal elastomers 11,[13][14][15][16][17]39,40 , shape memory polymers 41 , hydrogels 10,12,24 , and others 25 ) and multimaterial structures 11,26 enable large structural deformation but face challenges in implementing fast control to refined structures. The design of shape-morphing process usually requires prerequisite modeling effort to be programmed into the fabrication process, and is therefore hard to reprogram on-the-fly (e.g., 3D printing 11,27 , magnetization 19,42 , laser or wafer-jet cutting 29,30,43 , mechanical buckling 28 ).…”

A Rod Theory for Liquid Crystalline Elastomers

“…Nematic elastic rods are slender, flexible structures made of liquid crystal elastomers (LCEs) [35,48,65,71,72]. Due to their stimuli-responsive material properties, they can convert light or heat into mechanical work, without the need for batteries, electric wires or gears [58,67].…”

“…Rods with an in-printed helical director field under a remotely controlled rotation were presented in [48]. Light-controlled bending and twisting of nematic rods were investigated in [65,71]. Theoretically, three-dimensional nematic cylinders under combined stretch and torsion were analyzed in [17], and a nonlinear beam model for photoresponsive structures was proposed in [30].…”

“…To achieve this, we adapt the strategy developed for morphoelastic rods in [46] (see also [34,45,47,49]), and apply the resulting model to specific scenarios leading to the formation of rods with non-trivial intrinsic curvatures. In particular, we consider rods with square or circular cross-section, and a nematic director uniformly aligned at a given angle relative to the longitudinal axis [65,71], or a helical director field [48]. In Sect.…”