Optically-responsive liquid crystal elastomer thin film motors in linear/nonlinear optical fields

Currently, there is significant interest in photo-excited self-oscillation systems utilizing a thin film of liquid crystal elastomer. However, studying their complex dynamic behaviors is challenging due to the inhomogeneity of the optically driven deformations. In this paper, we derive the asymptotic relationship of the thin film motor module in the inhomogeneous light fields by establishing a theoretical framework for the module. Subsequently, the asymptotic relationship of the module is applied to investigate the liquid crystal elastomer thin film-mass systems in both linear and nonlinear light fields. Through the use of asymptotic relationship, three dynamic behaviors of the system are discovered, namely, damper, spring and motor, each characterized by different effective viscoelasticity coefficients. In particular, the liquid crystal elastomer motor can operate more efficiently in the linear optical field, requiring less energy to generate the same amplitude of self-oscillation as in the nonlinear field. The proposed asymptotic relationship of the optical thin film motors under both linear and nonlinear optical fields can be readily referenced in other research, offering convenience and guidance for soft robotic motors, energy harvesters, and micro-machines.