Molecular-Level Recognition of Interaction Mechanism between Graphene Oxides in Solvent Media

The interaction between graphene oxide (GO) in solvent is a fundamental basis in its colloidal suspensible stabilization, which is important in the solution processing technique for the preparation of processable graphene sheets. In this work, the potential of mean force (PMF) between two GO nanosheets in solvents was simulated to quantify the interaction mechanism. It was observed that GO sheets in water with various oxidization levels demonstrate diverse interacting performances. The neutral GO sheets generally show weak attractive interaction with kinetic reversible aggregating/dispersing stability. However, the deprotonated GO sheets with negative charges have strong colloidal stability, which is due to the long-range electrostatic repulsion arising from the charged functional groups. The interaction of GO sheets is a delicate balance of the interacting force between GOs themselves and the corresponding solvation force. The detailed PMF analysis identifies the distinct roles of water in the contribution to GO interactions. For neutral GO sheets, the solvation force provides repulsive action, aiding the GO dispersion. However, for the negatively charged GO sheets, the solvation force contrarily exhibits attractive hydrophilic interaction due to the strong water affinity of deprotonated carboxyl groups. In the nonpolar benzene solvent, the PMF profile displays strong aggregation trend compared with the water solvent. The solvation force in benzene solvent could not afford sufficient repulsive interaction to overcome the attractive interaction between GO sheets. This behavior reflects the specific effect of benzene solvent on functional groups. Our simulation results present new a molecular-level understanding of GO interactions in solvents.