Mechanics of light-fueled bidirectional self-rolling in a liquid crystal elastomer rod on a track

Self-sustained motions, which absorb energy from a steady environment to maintain continuous movement, hold great potential for applications in soft robotics and energy harvesting. However, achieving directional flexibility in such systems often requires adjusting material expansion-contraction properties, light source positioning, or structural design, limiting broader applications of active-material-based systems. In this paper, we propose a light-fueled self-rolling liquid crystal elastomer (LCE) rod system, which are capable of bidirectional self-rolling on a track. Based on heat conduction theory and the optical-thermally responsive LCE model, we establish a theoretical model to investigate the self-rolling of LCE rod, deriving the light-driven lateral curvature and driving moment of the rod. The theoretical results show that the self-rolling of the LCE rod results from the driving moment induced by the shift of the center of gravity, and the self-rolling velocity can be determined by system parameters. A few experiments demonstrate that adjusting the track width can alter the self-rolling direction of the LCE rod, and increasing the heat flux can enhance the self-rolling velocity, which consistent with theoretical predictions. The self-rolling LCE rod presented in this paper offers the benefits of a straightforward structure, bidirectional rolling capability, and precise control over small-area light sources. The theoretical results obtained offer insights into controlling and enhancing multifunctional motion, with significant implications for soft robotics, energy harvesting, and actuator technologies.