Photoresponsive Non-Cross-Linking Film Actuator that Bends Away from a Light Source

Azobenzene-based photoresponsive polymer film actuators normally bend toward an ultraviolet (UV) source, in which their photosensitive mesogens are stabilized in cross-linking polymer networks. Herein, we synthesize a non-cross-linking liquid-crystalline (LC) polymer film actuator, in which the photoresponsive azobenzene mesogens are aligned in a perpendicular direction to the non-cross-linking polymer chains. Upon exposure to UV light (? = 365 nm), the trans-to-cis isomerization generates expanding strength along the parallel direction with respect to the polymer main chains, which causes the film actuator to bend away from the light source. After prestretching the film actuator at 120 ? to enhance its perpendicular alignments of the azobenzene mesogens, its photoresponsive performance can be improved. As a result, the film actuator shows flexible and multifarious motions not only in air but also in liquid environments, making it more adaptable to sensing systems, soft robots, and artificial muscles.