Programmable Light‐Activated Gradient Materials Based on Graphene–Polymer Composites

Recently, adaptive programmable materials capable of changing their shape to perform complex motions in response to an external stimulus have attracted tremendous interest. The shape‐changing abilities rely heavily on the non‐linear response of a localized area, where generally an external stimulus would cause distortion due to non‐uniform volumetric changes. Hence, creating materials with heterogeneous compositions and structures have become an effective strategy to achieve the non‐uniform volumetric changes. Here, a versatile strategy that harnesses the concepts of structural and compositional gradients to guide the design of programmable light‐activated materials with continuous changing structures and their correspondingly responsive behavior are developed. These materials compose of a bilayer structure including ultraviolet‐cured Norland Optical Adhesive (NOA) 73 support layer and a structural and compositional gradient layer of polyethylenimine (PEI)‐modified graphene oxide (GO) complexes. The volumetric mismatch between these two layers leads to the reversible three‐dimensional deformation of PEI‐GO/NOA 73 bilayers. The PEI density and the extent of GO reduction lead to different light‐sensing abilities, which result in different extent of deformation and deformation/reversal speed. By controlling the composition of each PEI‐GO segment, programmable light‐activated actuations, such as helical buckling with varying pitch‐sizes of a gradient‐based PEI‐GO/NOA 73 actuator are demonstrated.