Simulated Tribological Properties of Pure and Mixed-Base PAO Oils

The appropriate mixtures of the differently branched PAO molecules can create the base PAO oils that provide excellent lubricating performance. In this simulation study, we investigate the lubricity of 22 PAO systems, formed by mixing the molecules with 1, 3, and 7 branches in the various ratios. The PAO molecules are modeled using the united-atom approach, where CH, CH₂, and CH₃ groups are represented as the different beads. Friction is detected based on its dependence on the mixtures and pressure. Analyses of the molecular shape and arrangement in the lubricants and the lubricant structure explain the lubrication mechanisms. The findings of this study are as follows. The all PAO systems exhibit low friction on the iron surfaces due to their molecular shape and ordered arrangement parallel to the sliding direction. The layered molecular structure formed near the sliding iron slabs reduces the boundary interactions and improves the lubrication. The blended PAO systems benefit from the intercalation between the small and large molecules, enhancing the shear behavior and overall lubrication. The PAO lubricants with a higher proportion of the branched molecules tend to provide better lubrication. The friction coefficient of the iron surfaces lubricated with the PAOs decreases as the pressure increases. As this is the systematic study of the multiple blended PAO systems, it may serve as a valuable reference for experimental researchers and those seeking suitable mixtures of PAO lubricants as well as evaluating their compatibility with additives. Additionally, the models established in this study can also be useful for conducting simulations.