Viscoelastic Dynamics of Photothermal-Responsive Liquid Crystal Elastomer Fibers

Liquid crystal elastomers (LCEs) with photo-responsive properties, typically driven by either photochemical or photothermal mechanisms, have found extensive applications as, for example, actuators in soft robots. However, intricate temperature-dependent viscoelasticity of LCEs poses a challenge, leading to a notable gap in the domain of dynamic models for photothermal-responsive LCE (PTR-LCE) fibers. Here, a fundamental framework is proposed for accurate modeling and real-time simulations of PTR-LCE fiber dynamics. The PTR-LCE fiber is described as a one-dimensional (1D) string model that decomposes the fiber deformation into active and passive parts, which are characterized by an order parameter and a temperature-dependent linear viscoelasticity model, respectively. Then, independent experimental measurements of model parameters are conducted, and a numerical algorithm is developed to solve the model, which is validated for convergence, time efficiency, and accuracy. Finally, the model is employed to simulate both open-loop and Proportional-Integral-Derivative (PID) control of actuators made of PTR-LCE fibers. The results confirm the advantages of this model over previous models. This work not only reveals the physical mechanisms underlying the PTR-LCE fiber dynamic behaviors but also provides inspirations for more efficient and precise soft robotic applications.