Molecular simulation of interfacial mechanics for solvent exfoliation of graphene from graphite
The interfacial force for exfoliating a graphene monolayer from graphite in solvent media was studied by restrained molecular dynamics simulations. Three solvents, N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and water, were considered. The interfacial structures show that NMP and DMSO have a stronger affinity with graphene surfaces. In the solvent media, there exists an inherent attractive force hindering the exfoliation, which is almost exclusively determined by the interaction between graphene sheets. Along the perpendicular exfoliation direction (relative to the graphene plane), the initial exfoliation is less dependent upon solvent conditions, and the subsequent exfoliation can be facilitated by the solvent-induced interaction. However, along the shift direction parallel to the graphene plane, the organic solvent provides a favorable driving force to assist the exfoliation, whereas water offers obstructing effect. The parallel shift of graphene requires less external power than the perpendicular shift for our simulated systems. The confined solvent molecules between graphene sheets play an important role in exfoliating and stabilizing graphene in solvent media. This result provides a microscopic understanding of the function of solvent-induced interaction in the solvent exfoliation of graphene.