Nanoscale ionic materials based on hydroxyl-functionalized graphene

Abstract

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.