Self-rotation of a liquid crystal elastomer rod under constant illumination

Self-sustaining systems can generate and maintain periodic or chaotic motion under constant external stimulation, and has potential applications in fields such as soft robotics, energy harvesting, and active machinery. However, self-sustaining systems often come with excessive oscillations and increased friction, which limit their applications. Unlike oscillatory self-sustaining systems, we have developed a novel steadily self-sustaining system, which is composed of a liquid crystal elastomer rod and a support sleeve. Experiments demonstrate that the liquid crystal elastomer rod on a support sleeve can self-rotate steadily and continuously under constant small area illumination. During the self-rotation, the shape of the liquid crystal elastomer rod remains unchanged, which avoids excessive oscillations and decreases friction. Based on a photothermal-responsive liquid crystal elastomer model, we derived the lateral curvature and the actuating rotation moment. Numerical simulations reveal that the liquid crystal elastomer system balances damping dissipation during motion by absorbing heat converted from constant illumination. The angular velocity of the self-rotation is influenced by parameters such as heat flux, heat transfer coefficient, length of the rod, and damping rotation moment. The theoretical predictions match the experimental results. The novel steadily self-rotating system not only has the advantages of maintaining shape and reducing friction, but also offers benefits such as structural simplicity, small illumination area, and higher energy efficiency compared to other steadily self-sustaining systems driven by large illumination areas or hot surfaces. This research is anticipated to offer valuable insights for applications in soft robotics, energy harvesting, and active machinery.