Supramolecular Hybrid Hydrogels from Noncovalently Functionalized Graphene with Block Copolymers

In recent years, graphene has become a prevailing topic in the materials community. Numerous applications of graphene have been generated, including gas sensors, photovoltaics, field-effect transistors, etc. In this paper, we demonstrate that graphene sheets could serve as a desirable inorganic constituent in constructing hybrid polymeric hydrogels via supramolecular routes, which currently is not so popular as the other applications. In this paper, graphene oxide (GO) nanosheets were modified by grafting beta-cyclodextrins first, leading to chemical converted graphene (CCG), and then noncovalently functionalized by block copolymers AZO-PDMA-b-PNIPAM via inclusion complexation. The resulted hybrid graphene inclusion complex (HGIC) was fully characterized by a combination of techniques including UV-vis spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Then, due to the thermo sensitivity of the PNIPAM block, HGIC solutions exhibited sol gel transition at elevated temperature. Rheology studies revealed that the gelation of the HGIC suprastructure took place much faster at a temperature close to but lower than the LCST of PNIPAM. It was also found that the gelation temperature increased with the ratio of degree of polymerization of PDMA block to PNIPAM block of HGIC suprastructures. On the basis of the results, a new possible gelation mechanism was proposed. The flexible and ultrathin 2D planar structure of graphene sheets exhibited unprecedented advantage in constructing the 3D network structure of the hydrogels, showing rapid sol gel transition at elevated temperature.