Researchers at Peking University, Jiangxi Normal University, the University of Science and Technology Beijing, and the University of Bristol have developed a liquid crystal elastomer (LCE) actuator reinforced with thiol-functionalized graphene oxide (FGO) that combines high mechanical toughness with an activation temperature close to human body temperature, addressing a longstanding tradeoff in soft robotics materials.
Illustration of the graphene oxide-reinforced liquid crystal elastomer actuator, showing its near-body-temperature activation and high fracture toughness.
Liquid crystal elastomers are widely studied for soft actuators and artificial muscles because they can undergo large, reversible, programmable deformations in response to heat, light, or other stimuli, and graphene oxide fillers have previously been used to boost their toughness through strong π-π interactions with the liquid crystal phase. But conventional LCEs face a persistent conflict: actuators tough enough for demanding, high-load robotic applications typically require activation temperatures above 100°C, which is impractical and potentially unsafe for devices meant to interact directly with the human body, while LCEs engineered for near-body-temperature activation have generally lacked the mechanical robustness for real-world use.
The team's approach combines three levels of engineering to resolve that conflict. At the molecular level, a biphenyl-based liquid crystal mesogen with lower phase stability shifts the material's thermal transition down toward physiological temperatures. At the network level, linear liquid crystalline polyurethane chains are physically interpenetrated within a crosslinked polymer network, allowing chain entanglement and hydrogen bonding to dissipate energy without the excess crosslinking that would otherwise stiffen the material. At the interface level, the functionalized graphene oxide strengthens the coupling between the polymer and filler, improving stress transfer while also adding photothermal responsiveness.
The resulting nanocomposite activates at approximately 40°C under load-free conditions, reaches a fracture toughness of 76.5 MJ/m³, and delivers a maximum work capacity of 567 kJ/m³ during loaded thermal actuation - toughness well above the roughly 3 MJ/m³ typical of conventional LCEs. The researchers demonstrated the material in body-temperature-responsive smart devices, pointing toward applications in soft robots designed for safe, direct human interaction.
