Graphene oxide/poly (N-isopropylacrylamide) hybrid film-based near-infrared light-driven bilayer actuators with shape memory effect

Smart actuators with fast and reversible changes towards external stimuli have attractive potentials in diverse applications. Here, we present the rational design and facile fabrication of graphene oxide (GO)/poly (N-isopropylacrylamide) (PANIPAM) hybrid film-based bilayer actuators, which display efficient and reversible bending/unbending behaviors in response to repeated cycles of near-infrared (NIR) light irradiations. Our bilayer actuator comprises a layer of GO, and a layer of GO/PNIPAM (GP) hybrid, taking advantages of the NIR absorbance and photothermal conversion capability of GO, along with the thermo-responsiveness of PNIPAM. Upon NIR light irradiation, GO converts absorbed light into heat, which subsequently triggers the shrinkage of PANIPAM chains, leading to the bending of the bilayer actuator. Owning to the shape inertness of GO to the NIR light, repeated irradiations of NIR light cause the bilayer to shrink/relax in an asymmetric manner, consequently leading to reversible bending/unbending behaviors of the bilayer actuator. Remarkably, our actuator shows templated bending orientation once exposed to NIR light, and exhibits shape memory effect due to the incomplete recovery of PNIPAM chains. This shape memory effect is retained in rectangular strips cut from the original disk-shaped bilayer and is exploited to selectively achieve either bending or twisting deformation. As an interesting example for potential practical utilization, a smart NIR light-driven forklift capable of lifting goods has been built by pinning one side of the bilayer film.