Nanoscale ionic materials based on hydroxyl-functionalized graphene

Nanoscale ionic materials (NIMs) are novel organic-inorganic hybrid materials consisting of inorganic nanocore covalently attached with charged corona that is electrostatically coupled to oppositely charged canopy. In this study, graphene-based NIMs were prepared from hydroxyl-functionalized graphene (G-OH) that acquired via nitrene chemistry. The obtained G-OH-based NIM exhibited fluidity at its equivalence point (pH 6.3) at room temperature; in contrast, the graphene oxide (GO)-based NIM appeared as a black solid at its equivalence point because of the relatively low -OH density on GO. X-ray photoelectron spectroscopy and thermogravimetric analyses revealed grafting densities for G-OH and GO-based NIMs of ca. one polymer chain per 21 and 94 graphene carbon atoms, respectively. Microstructure analyses indicated the even dispersion of graphene nanosheets in NIMs. Rheological properties of G-OH-based NIMs could be adjusted over a wide range through variation of the volume fractions of canopy (Jeffamine M-2070 polyetheramine). G-OH-based NIMs also showed different viscoelastic behaviours from that of a G-OH-canopy physical mixture with similar graphene content. Thermal analyses showed that the crystallization temperature of canopy in G-OH-based NIMs decreased compared to that in physical mixtures. Cold crystallization was apparent during the heating cycle for G-OH-based NIMs, which did not exist for the physical mixtures. Furthermore, G-OH-based NIMs showed even dispersion and months-long stability in water and many organic solvents, indicating its amphiphilic nature. The unique properties of graphene-NIMs hold great potential for applications employing graphene-based materials.