Abstract
Liquid crystalline network (LCN) actuator normally deforms upon thermally or optically induced order-disorder phase transition, switching once between two shapes (shape 1 in LC phase and shape 2 in isotropic state) for each stimulation on/off cycle. Herein, we report an LCN actuator that deforms from shape 1 to shape 2 and then reverses the deformation direction to form shape 3 on heating or under light only, thus completing the shape switch twice for one stimulation on/off cycle. The deformation reversal capability is obtained with a monolithic LCN actuator whose two sides are made to start deforming at different temperatures and exerting different reversible strains, by means of asymmetrical crosslinking and/or asymmetrical stretching. This desynchronized actuation strategy offers possibilities in developing light-fueled LCN soft robots. In particular, the multi-stage bidirectional shape change enables multimodal, light-driven locomotion from the same LCN actuator by simply varying the light on/off times.
Highlights
Liquid crystalline network (LCN) actuator normally deforms upon thermally or optically induced order-disorder phase transition, switching once between two shapes for each stimulation on/off cycle
The LCN actuator, capable of executing two-stage shape morphing towards opposite directions on only stimulation on or off, is fabricated based on the concept of “desynchronized actuation”
It means that the two sides of a LCN strip start to deform at different temperatures and impose different strains
Summary
Liquid crystalline network (LCN) actuator normally deforms upon thermally or optically induced order-disorder phase transition, switching once between two shapes (shape 1 in LC phase and shape 2 in isotropic state) for each stimulation on/off cycle. In all cases, as the light-induced gradient and its variation over time is essential, when light is off, the strip cannot bend and flatten again, because the cooling is uniform for photothermally-based actuators, or because the photoreaction is ceased for photochemically driven actuators[41,42] As shown below, this apparent deformation reversal (bending/unbending), which is the intermediate state as the LCN sample moves to the equilibrium state under irradiation, is different from the built-in deformation-reversal capability explored in the present study. Since the deformation-reversal behavior stems from structurally inscribed desynchronized actuation, it occurs when the LCN is subjected to uniform heating and can be observed in a thermal equilibrium state Using this strategy, it is possible to adjust or control the deformation-reversal actuation in terms of the magnitude and the shape-changing directionality. As a proof of concept, by taking advantage of the fact that one deformation-reversal actuation cycle can be divided into multiple stages, we prepared LCN actuators that can execute light-driven locomotion in multiple fashions (referred to as multimodal locomotion) by tuning only the light-on/off times for desired temperature variations
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