Molecular Dynamics Analysis of Friction Properties of Multi-Layer Graphene Oxide as a Lubricant Additive

Abstract

Carbon-based nanomaterials have been employed as lubricants in industrial settings due to their low-friction properties. Among them, graphene oxide (GO) has been employed in a variety of applications because it is more hydrophilic than graphene and disperses easily in polar solvents. Furthermore, it has low production costs and low environmental impact. These properties render it a promising new lubricant additive with the potential to supplant long-used organometallic lubricant additives. It has been reported that GO exhibits low friction not only in water lubrication, but also in oil lubrication with GO-modified alkyl groups. In this study, a hierarchical GO model was constructed by molecular dynamics simulations using the reactive force field (ReaxFF) and compared with friction experiments. The analysis revealed that GO is stable in water but sensitive to pressure in oil. Sheets in contact with oil showed instability, moving from side to side. Furthermore, the alkyl-modified GO appeared to be integrated with the oil, suggesting that the alkyl groups contribute to the observed low-friction properties. These results are in qualitative agreement with the experimental data and indicate that the behavior of GO is solvent dependent.