A phototunable self-oscillatory bistable seesaw via liquid crystal elastomer fibers

Self-oscillatory systems can sustain continuous motion under constant stimuli, yet their practical applications are restricted by intrinsically controlled oscillatory frequencies. Through assembly of a photothermally-responsive liquid crystal elastomer fiber, a spring, a mass block and two rigid rods with fixed angle, we experimentally developed a self-oscillatory bistable seesaw, achieving active regulation of oscillatory period. The bistable seesaw exhibits back-and-forth toppling, including forward toppling and backward toppling, under steady illumination. To explore the underlying mechanism, a theoretical model was developed and its self-oscillatory behavior was examined. The self-oscillation arises from the photothermal-mechanical energy conversion and switching in center of gravity. Influenced by the photothermally-driven contraction in liquid crystal elastomer, the critical strains can be adjusted by modifying the geometric dimensions. Notably, adjusting the heat flux and contraction coefficient modulates the duration of forward toppling, thereby enabling the period regulation of the bistable seesaw. Distinct from conventional self-oscillatory systems, the proposed bistable seesaw effectively resolves the inherent conflict between system stability and frequency regulation, demonstrating considerable potential for soft robotics, sensors, and energy harvesters.