Mechanically strong Janus poly(N-isopropylacrylamide)/graphene oxide hydrogels as thermo-responsive soft robots

Simple preparation of stimuli-responsive hydrogels with good mechanical properties and mild stimuliresponsiveness is essential for their applications as smart soft robots. Mechanically strong Janus poly(N-isopropylacrylamide)/graphene oxide (PNIPAM/GO) nanocomposite hydrogels with stimuli-responsive bending behaviors are prepared through a simple one-step method by using molds made of a Teflon plate and a glass plate. Residual oxygen in the air bubbles on the Teflon plate surface affects the polymerization and hence the cross-linking density, leading to the different swelling/deswelling rates of the two sides of the gels. Therefore, the hydrogels exhibit bending/unbending behaviors upon heating/cooling in water. The incorporation of GO nanosheets dramatically enhances the mechanical properties of Janus hydrogels. Meanwhile, the photo-responsive property of the GO nanosheets also imparts the hydrogels with remotecontrollable deformation under IR irradiation. The application of the Janus PNIPAM/GO hydrogels as thermo-responsive grippers is demonstrated.