Molecular Dynamics Study of the Interactions of Graphene Oxide and Sandstone Surfaces

Molecular dynamics simulations were employed to investigate the transfer and detachment energies of graphene oxide (GO) and pristine graphene sheets at liquid-liquid and solid-liquid interfaces. Using the umbrella sampling technique, the potential of mean force profiles were calculated to assess how the degree of oxidation of the GO sheets, the chemistry of the surface of a sandstone rock, and the nature of reservoir fluids influence these processes. Water and toluene were selected as the aqueous and crude oil models of the reservoir fluids, respectively, while the (001) crystallographic plane of the α-quartz at Q3 and Q4 saturations was used to mimic the sandstone surface. The results revealed that the Q3 surface, rich in silanol groups, is hydrophilic while the Q4 surface, composed of siloxane, exhibits hydrophobic behavior. GO sheets display interfacial activity that increases with the degree of oxidation, promoting solubility in the aqueous model and reducing the affinity for the crude oil model. Conversely, pristine graphene is non-interfacially active and preferentially resides in the toluene. On the other hand, the detachment of the sheets from the rock surface is strongly dependent on its surface chemistry, the degree of oxidation of the sheet, and the characteristics of the reservoir fluid. The detachment of GO and pristine graphene is energetically most favorable from the Q3-aqueous model interface (free energy of less than 12.8 kcal/mol), followed by the Q4-crude oil model interface (free energy of less than 53.8 kcal/mol). The highest detachment energies occur from the Q3-crude oil model and Q4-aqueous model interfaces (free energy of less than 90.7 kcal/mol), with inverse trends in sheet behavior, highlighting the complex interplay of interfacial interactions.