A nematic liquid crystal elastomer rotary engine.

Nematic liquid crystal elastomers (NLCEs) could perform as soft actuators because they generate greater contraction stress than ordinary rubber in response to a temperature rise of several tens of Kelvin. In this study, we follow the Wiegand rubber motor design, and develop a prototype star-shaped type rotary engine with four to twelve NLCE contractile elements, in which multiple NLCE actuators contract due to the photo-thermal effect to rotate the crankshaft. Continuous rotational motion under white light was experimentally confirmed. Through theoretical modeling, it was clarified that in this system, the contraction of the NLCE actuators generates a driving torque, while a viscoelasticity-originated internal friction resists the rotation, thus producing rotation at constant speed. Effects of the number of NLCE elements, light power, initially applied pre-tension, and the system size on the engine performances, such as rotation speed, output power, energy efficiency, are explored. Given that the physical properties of NLCE (liquid crystallinity, phase transition temperature, and viscoelastic properties) are linked to the engine performance, the present engine system with the analysis protocol is expected to serve as a test platform for future evaluation of NLCE actuation performance.