Biomimetic Graphene Actuators Enabled by Multiresponse Graphene Oxide Paper with Pretailored Reduction Gradient

The strong interaction between water molecules and graphene oxide (GO) enables moisture-responsive graphene actuators, revealing great potential for soft robots. However, current strategies for developing smart graphene actuators fail to tailor their material property gradient in a controlled manner, and the driving manner is usually limited to single stimulus actuation. Here, a facile preparation of humidity/thermal/light multiresponsive graphene actuators by sequential vacuum filtration of GO and reduced GO (RGO) aqueous solutions is reported. The photoreduction degree of RGO layer is tuned precisely beforehand by changing ultraviolet (UV) light irradiation time, and thus a pretailored reduction gradient along the normal direction of the GO/RGO bilayer paper would form in a highly controlled manner. Taking advantage of the competitive water adsorption between the GO and RGO layers, as well as the thermal-, light-promoted desorption, the GO/RGO bilayers deform in response to moisture, light, and temperature changes; and the deformation degree can be modulated by controlling the gradient of oxygen-containing groups (OCGs). As a proof of principle, a humidity-responsive graphene mimosa and a humidity/thermal/light multiresponsive graphene actuators are fabricated. The GO/RGO bilayer paper with pretailored reduction gradient holds great promise for easy fabrication of biomimetic actuators that enable performing predictable deformation.