Crystal actuator based on a thermal phase transition and photothermal effect

Mechanically responsive materials have been increasingly explored, mainly in terms of photoisomerization. Here, we report the bending actuation of salicylideneaniline crystals induced by a thermal phase transition and photothermal effect. Long rod-like crystals bent reversibly on repeated heating and cooling near the transition temperature. The bend motion was also induced by the photothermal effect under ultraviolet (UV) and visible light irradiation, with and without phase transition. The photothermal-based temperature rise at the irradiated site of the crystal edge resulted in localised elongation near the crystal surface and slight bending due to the temperature gradient in the thickness direction. This bending motion was amplified by tip displacement at the opposite end of the long rod-like crystal. Finally, high-frequency bending actuation of 25 Hz was achieved by pulsed UV irradiation. Thus, the results of this study demonstrate the potential and versatility for mechanical crystal development based on the photothermal effect.