UC San Diego

Soft actuator is a promising candidate for replacing a traditional rigid materials-based actuator when the actuating system requires human compatibility, large degree of freedom for the motion, low fabrication cost, and simple body structure. Among many soft materials, liquid crystal elastomer (LCE) is one of the most advantageous soft active material due to their large macroscopic deformability coupled with molecular level anisotropy. Patterning of LCE with precise control of molecular alignment can generate diverse actuations. In addition, different types of actuation of LCE can be induced by various external stimuli such as heat or light.

In this study, we demonstrate radially patterned LCE with predesigned stretch field using a strain engineering technique which is facile, effective, and does not require any sophisticated setup. The radially patterned LCE exhibits fully reversible undulating deformation upon heating or swelling, attributed to the constrained expansion of radially patterned LCE in hoop direction. By applying the strain engineering technique, we design different LCE structures which exhibit diverse actuations like bending, rolling, crawling, or jumping. Incorporation of carbon nanotube (CNT) in the LCE allows photoresponsivity of LCE-CNT composite due to the photothermal effect of CNT. We prepare LCE-CNT rod with molecular alignment in its longitudinal direction which shows heliotropic behavior with multi-directional bending under the light irradiation rather than conventional uni- or bi-directional bending. The bending is induced by the contraction gradient of LCE-CNT rod in thickness which is maximized on the surface towards light, so the bending direction can be tuned by controlling the position of light source. Using the similar LCE or LCE- CNT rod, we show unusual rolling phenomena in which the LCE or LCE-CNT rod keeps rolling while maintaining its initial curvature in the same direction continuously induced by simply placing them on a homogeneously hot flat surface or under the visible light irradiation. Such non- intuitive autonomous rolling phenomena is induced by coupling of inhomogeneously distributed supporting force and gravity, which is triggered by continuous bending deformation of the rod during rolling. We also design a light-driven soft robot based on an arch shape LCE-CNT structure with magnet pieces on each end that performs crawling, squeezing, and jumping motions inspired by deformation traveling of inchworm locomotion and power amplification mechanism of jumping fly larva. The soft robot can perform different motions by switching its shape between arch and closed loop shape under different light irradiation modes, which enables fully reversible biomimetic motions.