Light-driven composite films with photomechanical salicylideneaniline crystals aligned in UV-curing resins for soft actuators

Photomechanical crystals—a subclass of crystalline materials that exhibit macroscopic deformation under light illumination—have applications in light-driven actuators and soft robots. However, they are associated with several drawbacks, such as size limitations to the millimeter scale and poor processability, which hinder their practical applications. Although several composite materials in which photomechanical crystals are aligned in a polymer membrane have been developed, the size of the photomechanical crystals has not been optimized, nor have the mechanical properties of the composite materials been investigated in detail. Here we demonstrated centimeter-scale, light-responsive, crystal–polymer composite films consisting of salicylideneaniline microcrystals and ultraviolet (UV)-curing resins. Desired-size single microcrystals were prepared by using the reprecipitation method or sublimation. Upon UV irradiation to the films, they bent away from the light source through photoisomerization or the photothermal effect, demonstrating their ability as an energy converter from light to kinetic work. The composite films exhibited distinct bending reversibility depending on the polymer matrix, originating from the polymer’s different mechanical properties. Our composites provide insight into the development of centimeter-scale photomechanical materials with high processability, and, ultimately, light-fueled actuators and soft robots. • Light-fueled crystal–polymer composite films have been developed. • Desired-size single microcrystals were prepared by reprecipitation or sublimation. • Mechanical properties of the polymer matrix governed the bending reversibility.