Multiphotoinduced Bending of Azobenzene-Modified Graphene Oxide/Poly(vinyl alcohol) Composite Films for Smart Devices

Here, we report a composite film that shows multibending behaviors upon ultraviolet/visible (UV/vis) and near-infrared (NIR) light irradiations. First, an azobenzene-modified graphene oxide (AZO-GO) hybrid was prepared by the covalently grafting of 4-(3-triethoxysilylpropyl-ureido)­azobenzene (TSUA) onto the surface of GO. A reversible change in the hydrophilicity of AZO-GO was observed upon UV/vis irradiations, due to the effective trans–cis-photoisomerization of azobenzene groups. Then, the AZO-GO hybrid powder was dispersed in ethanol and homogeneously mixed with the poly­(vinyl alcohol) (PVA) aqueous solution to give a uniform and thin composite film (AZO-GO/PVA) with good flexibility by casting. Upon UV irradiation, this film bends rapidly toward the light source with a large amplitude and recovers to the original shape upon subsequent visible irradiation, due to the reversible trans–cis-photoisomerization of azobenzene groups. Upon NIR irradiation, the film curls slightly away from the light source, which is considered to be caused by the photothermal effect of the GO component. This composite film is also low-cost and uses facile manufacturing, with enhanced mechanical properties. Finally, by combining three pieces of the composite films, mimicking the reversible grabbing–release motions of a claw upon UV/vis irradiation was achieved.