Chiral deformation reversal of liquid crystal polymer actuators

Abstract

The chiral deformation of a conventional helical actuator is unidirectional in each activation (stimuli-on) process and in each recovery (stimuli-off) process, which means that the twisting direction remains the same regardless of the nature of deformation (either winding or unwinding or helix-inversion). In these cases, a complete stimuli-switching cycle is necessary for the realization of a bidirectional helical deformation process that comprises a reversal of twisting direction. Here, we achieved bidirectional and even multi-directional helical shape evolution in each stimuli-on (or off) process. The strategy relies on, on one hand, asymmetrically crosslinking and/or elongating the two sides of a photocrosslinkable liquid crystal polymer (LCP) monolith, and on the other hand, tailoring the uniaxially aligned polymer strip to form an off-axis mesogen orientation. We obtained a wide variety of helical actuators capable of reversing their twisting directions by only cooling (or heating). The mechanisms of these various chiral deformation-reversal behaviours and the two observed reversals of the twisting direction during cooling have been elucidated.