Mastering the photothermal effect in liquid crystal networks: a general approach for self-sustained mechanical oscillators

Chemical networks and molecular switches dominate the area of research geared toward macroscopic motion of materials. A counter-intuitive approach to create self-sustained oscillation by light irradiation of ordinary photostabilizers in splay-aligned liquid-crystalline networks made from commercial mesogens is developed. Photostabilizers or any molecules that are able to quickly dissipate the absorbed light through heat, by vibrational and/or rotational modes, can reach self-oscillating macroscopic motion where self-shadowing plays a critical role. The mechanical self-oscillation is linked to temperature oscillations and the asymmetric response over the film thickness. Only a localized responsive zone, acting as hinge, activates the oscillation of a beam-shaped device. The outcome of this research is extended from UV to near-IR actuation, making bulk applications to convert sunlight into mechanical work within reach.