Sequentially Autonomous Rolling of Liquid Crystalline Elastomers with Tunable Actuation Temperatures
The autonomous liquid crystalline elastomer(LCE)actuators have garnered increasing attention owing to their ability to sustain continuous motion without the need for external manual control.However,most autonomous LCEs are only capable of achieving self-sustained locomotion under specific single conditions(or within a small temperature range)due to their simplistic chemical design.This study begins with a twisted ribbon-shaped autonomous LCE,wherein precise control over the working temperature is attained by manipulating the network cross-linking density and incorporating non-liquid crystal co-monomers.The result shows that the cross-linking density has a significant impact on both the actuation performance and mechanical properties of LCEs,thereby influencing working temperature range and actuation speed.Specifically,as the amount of crosslinkers decreases,the actuation strain increases from 60％to 90％while the Young's modulus decreases from 21 MPa to 6 MPa.Due to the compromise of these two properties,the self-rolling capability would be constrained by either excessively high or low levels of cross-linking densities.The optimal performance is observed when the cross-linker ratio is in a moderate state,resulting in a wider range of actuation temperatures and faster moving speed.Beyond that,the incorporation of non-liquid crystal co-monomers also plays an important role in the actuation of LCEs.Different from the cross-linking density,both actuation performance and mechanical properties decrease significantly as the content of co-monomers increases,leading to a notable reduction in the temperature range required for actuation.The phase transition temperature of LCE even disappears when the co-monomer content exceeds 25 wt％,resulting in a loss of autonomous motion.Overall,the aforementioned methods enable the easy achievement of autonomous LCE actuators with diverse working temperature ranges.Sequential autonomous rolling can be accomplished during both the heating and cooling processes,owing to the distinct actuation temperatures exhibited by different LCE actuators.This tunable working temperature of autonomous LCE actuators will significantly broaden the scope of material design for soft robots.
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