Soft Actuators Based on Liquid Crystal Elastomers and Laser-Induced Graphene

Laser induced graphene (LIG) is a porous conductive carbon material produced by laser-induced pyrolysis of polymer precursors with applications in soft electronics/robotics and wearable electronics, among others. LIG conductors are conveniently created in a single synthesis/patterning step by laser scribing with a CO₂ or UV laser onto a polymer precursor such as polyimide. A subsequent transfer of the LIG onto a stretchable support such as polyurethane (PU) is used to create soft, flexible and stretchable LIG conductors. These soft conductors are then used in a composite with a liquid crystal elastomer (LCE), where the LIG acts as a joule heating element. The LCE is synthesized via click chemistry and poured into a mold where a partially cross-linked elastomer is created. The partially cured elastomer is pre-stretched and fully cured by UV irradiation. The LIG/PU and LCE are bonded together to form a multi-composite soft actuator. By applying a current to the LIG heating elements, a nematic-isotropic transition is induced in the LCE, resulting in contraction of the actuator. The contraction can be reversed by turning off the current and cooling the actuator. An linear actuation strain of about 60% is achieved. The combination of LIG as a heating element and LCE as an active actuation material is a promising approach to bio-inspired actuators with comparable performance to muscles.