Computer Aided Design of Graphene Based Lubricants for Electric Vehicle

Layered compounds, such as graphite and molybdenum disulfide, have a structure that molecular sheets are stacked in layers, and are commonly used as solid lubricants because they exhibit low friction. Among them, graphene oxide can be synthesized by oxidizing graphene, and is used in electronic devices because it is used as electrical insulator and has high mechanical strength. In addition, since it is hydrophilic than graphene, they can be easily dispersed in polar solvents. This mean it is usable both in water and oil environment. Moreover it has low environmental impact, and is low cost, so it is expected to be used in a wide range of applications. However, the mechanism of graphene oxide's low friction has not been elucidated. In this study, new molecular models are presented of graphite and multilayer graphene oxide sheets with oxygen contents of 20, 40, and 60 %, and calculate molecular motion. The results of structural relaxation calculations in this simulation confirmed that the film thickness and interlayer distance of graphene oxide increased with increasing oxygen content, is consistent with the results of experiments using XRD in previous studies. In addition, friction simulations are performed under both dry and with water added conditions. The results of the friction simulation confirmed that the friction behavior is quite different between graphite and graphene oxide. From this, it is suggested that graphene oxide does not have a low-friction mechanism like pure graphite. Especially, the effect of hydrogen bond of the lubricant water and the polar part of graphene oxide may be essential for the low friction.