Additivation of MoS2 nanosheets to synthetic poly-alpha-olefins base oils: A theoretical study of nanolubrication

Abstract

A theoretical study considering Density Functional Theory and classical Molecular Dynamics simulations is reported on the study of the behavior of model poly-α-olefins base oils interacting with 2D MoS2 monolayers. 2D materials offer a promising route to enhance anti wear and friction reduction. Among them, MoS2 show a set of specially favorable properties. The objective of the present work is to develop a nanoscopic characterization to show the roots of the use of 2D MoS2 monolayers as additives that reduce friction and wear with respect to plain lubricants. Three different types of hydrocarbons are considered, including the most relevant features of these oils: linear, star-like and branched compounds. The reported results show a large affinity of the three compounds for the monolayer surface, leading to very efficient adsorption guided by van der Waals interactions as well as by certain charge transfer toward the hydrocarbon. The development of adsorbed layers on the surface leads to changes in the base oil properties although being concentrated in a region close to the monolayer, with lower effects at larger distances. The presence of hydrocarbons with very different geometries hinders highly ordered molecular packing beyond the layer in direct contact with the surface. Nevertheless, the rearrangements on top of the MoS2 surface will lead to large changes in the base oil behavior for lubrication purposes, enhancing tribological and anti-wear properties of MoS2 nanosheet additivated poly-α-olefins base oils.