Multi-stimulus responsive soft actuator with thermotropic shape memory and local magnetic programming properties

Abstract

Soft materials possess the ability to deform or change shape when subjected to external stimuli, which makes them commonly used in the field of soft actuators. Under the actuation of single excitation such as light, heat, electricity, or magnetism, the deformation or motion mode of most soft actuators is monotonous. To achieve a multi-stimulus responsive actuation mode, the soft composite material LCE-CNT/MRF/Ecoflex (LCME) is developed by assembling liquid crystal elastomer (LCE) containing carbon nanotubes (CNTs), magnetorheological fluid (MRF) and Ecoflex. Among them, the additive-free high-performance MRF is prepared by mixing ionic liquid and silicone oil as carrier liquid, and provides magnetic actuation characteristic for LCME. The LCE is a mesh structure material formed by embedding mesogens into elastic polymers and moderate cross-linking them, possessing both soft elasticity and thermotropic shape memory properties. Assisted by the photothermal effect of CNTs, the rising temperature induces the rearrangement of mesogens in LCE containing CNTs (LC), allowing the LC to achieve reversible bidirectional deformation between an initial configuration and a thermotropic configuration. Under the multi-excitation actuation of photothermal effect and magnetic field, the LCME can perform bidirectional crawling and in-situ steering on a plane. This work demonstrates that multi-excitation actuation is beneficial in enriching the motion modes of soft actuators and points out a potentially promising direction for the development of soft robots.