Synergistic lubrication of organic friction modifiers in boundary lubrication regime by molecular dynamics simulations

The synergistic effect of organic friction modifiers (OFMs) combining glycerol monolaurate (GML) and tri-n-octylamine (N888) in base oil is studied by molecular dynamics simulations. The adsorption and shear behaviors indicate that the triple-chains N888 molecules intersperse among the long-chain GLM molecules to form an intercoordination adsorption film. The system with a number ratio of 3:1 of GML to N888 shows a better synergistic lubrication with the lowest friction coefficient. The chemisorption of GML molecules on Fe2O3 surface is verified by density function theory. High shear velocity accompanying friction heat causes adsorption film breakage and high friction, while contact pressure conduces to friction reduction. The synergistic lubrication is attributed to the interface slip between base oil and OFM films, rather than the interlaminar shear caused by an imbalanced combination or high shear velocity.