Molecular Dynamics Study on the Mechanism of Graphene Oxide to Destabilize Oil/Water Emulsion

Previous experiments have demonstrated the capability of graphene oxide (GO) to destabilize oil-in-water (O/W) and water-in-oil (W/O) emulsions, although there are debates on the underlying mechanism. Using molecular dynamics simulations, this work targets an atomistic-level understanding of the mechanism for GO to destabilize O/W and W/O emulsions in the presence of violanthrone-79 (VO-79), a model compound for asphaltene. For both types of emulsions, a GO/VO-79 binary film is formed on the oil/water interface, which can stabilize VO-79 on the interface. Detailed structural analysis shows that the majority of GO in the binary film is parallel to the interface and cause VO-79 to align with them, changing the original interface morphology. The results favor the mechanism that GO destabilizes W/O or O/W emulsions by first forming a film around the emulsion droplets and then enhancing the adhesion between droplets, or between a droplet and the macroscopic oil/water interface, through film–film interactions. Additional interfacial tension (IFT) calculations confirm that GO can increase the toluene/water IFT in the presence of VO-79, which is beneficial for emulsion destabilization.