Novel insights on the graphene oxide nanosheets induced demulsification and emulsification of crude oil-in-water emulsion: A molecular simulation study

Numerous experimental results demonstrated that graphene oxide (GO) nanosheets could not only stabilize but also destabilize the crude oil-in-water emulsion. The interfacial property of GO and its interaction with surface-active components in crude oil may be responsible for the contradictory results, which is rarely reported and may be hardly explored via the experiments. Then molecular dynamics simulation method is employed to analyze the interfacial interaction between GOn nanosheets with various surface charge densities and asphaltene molecules in crude oil. The radial distribution function (RDF), two-dimensional number density distribution, and molecular orientation analysis are calculated to systematically explore the effects of GOn on the asphaltene interfacial distribution. The GOn-asphaltene binary film stability is evaluated at the macroscopic level via the steered dynamic simulation, which is further investigated by reduced density gradient (RDG) approach to visualize their intermolecular interaction. The results show that the GO1 with higher surface charge density exhibits greater repulsion (∼5000 kJ/mol) with asphaltene-1 (ASP1), which can effectively disrupt ASP1 interfacial arrangement and destabilize the O/W emulsion. Whereas, the generated n-π*, π-π stacking, and cation-π molecular interaction between GOn with lower surface charge densities and asphaltene should be responsible for the great emulsion stability. In a word, this study firstly proposed the novel understanding about the underlying mechanism of GOn caused demulsification and emulsification.