Humidity-sensing and light-controlled steering azobenzene liquid crystal elastomer actuators

A main-chain liquid crystal elastomer (LCE) with amino-azobenzene mesogens was synthesized via thiol-acrylate Michael addition reaction and used to make rod actuators with aligned mesogens. The use of amino-azobenzene mesogens endows the LCE actuator with dual capabilities of colorimetric humidity sensing and light-controlled rolling motion on a hot substrate surface. On the one hand, a simple acid treatment results in protonation of surface amino-azobenzene moieties, enabling the LCE to change color reversibly depending on the relative humidity of its environment, with high humidity leading to deprotonation and low humidity prone for protonation. On the other hand, for LCE rod actuator rolling on a hot surface, localized light irradiation perturbs this self-sustained motion through photoisomerization and photothermal effects, achieving light-controlled braking, reversal, and steering. The irradiation intensity and position precisely modulate the parking time (duration of still state) and the curvature change, allowing navigable and obstacle-avoiding locomotion. This study demonstrates an integrated strategy to couple thermal and optical stimuli within a fully azobenzene-based LCE system, opening new opportunities for adaptive soft actuators and robots.