Modeling of a self-swimming thick-walled liquid crystal elastomer ring with a paddle on a hot liquid surface

Thermally responsive machines utilize thermal energy from the environment as a source of power, and have many unique advantages including no electronic equipment, self-supplementary energy, and self-adaptation to their environments, and they are closer to biological motion in form and function. In this study, a thick-walled Liquid Crystal Elastomer ring with a paddle structure is innovatively proposed, which uses thermal energy as fuel to perform self-sustained rotation and horizontal movement on a hot liquid surface. Based on the theoretical model and the well-established temperature field equations, the temperature distribution of the cross-section of the ring is given. Subsequently, the driving torque of the ring self-swimming is deduced, and the rotation and translation velocities of the ring are obtained. The findings reveal two motion modes of the ring on the hot liquid surface, namely, static mode and self-swimming mode, which arises from the competition between the thermally-induced driving torque and the friction torque. Moreover, the quantitative effect of each parameter on the rotation and translation velocities is analyzed, and the threshold values that distinguish the static mode from the self-swimming mode are given. Notably, there exists an optimum inside-outside radius ratio, and dimensionless density that maximize the rotation and translation velocities. The thick-walled ring self-swimming system has promising applications in the design and manufacture of soft robots, micro-machines, and energy harvesters.