Thermal Actuators Relying on Elastomer-Dispersed Liquid Crystals: From Imines with Supramolecular Chirality and Ferroelectricity to Soft Robots.

Abstract

The locomotion of various organisms relies on the alternated elongation-contraction of their muscles or bodies. Such biomimicry can offer a promising approach to developing soft robotic devices with improved mobility and efficiency. Most strategies to mimic such motions rely on reversible size modifications of some materials upon exposure to external stimuli. An example is the combination of liquid crystals (LCs) with elastomers that afford materials with reversible and programmable shape morphing upon heat treatment. This strategy is supposed to involve mainly liquid crystalline elastomers or liquid crystalline networks, but low molecular weight LCs were disregarded. Unlike the previous routes, we utilized a new type of thermal actuator, i.e., elastomer-dispersed LCs (EDLCs), where the LCs rely on small organic molecules, i.e., salicylaldimines with 1,3,4-thiadiazole core and silane or siloxane as mobility units. The individual components of EDLC are not chemically bound and have the advantage of retaining their intrinsic properties. By combining their particularities, herein we highlighted: rare molecules with supramolecular chirality and piezo-/ferroelectricity, new thermal actuators with >340% strain actuation, programmable twisting actuation through helical patterning of elastomers with cholesteric LCs, and crawler and walker soft robots, which show bidirectional gait with high speeds up to 2 mm s^-1.