Interaction Models and Molecular Simulation Systems of Steel–Organic Friction Modifier Interfaces

Ab-initio based benchmarking and improvements of molecular mechanics models for organic friction modifier (OFM) additives used in lubricants are presented. We found the generalized amber force field (GAFF2) appears well suited to model oil-steel interfaces moderated by fatty acids. However, explicit refinements are needed for describing the interactions of fatty acid glycerol esters with steel surfaces and were thus implemented into our OilF force field suite. Apart from analyzing single OFM molecule association to steel, we present a systematic scheme for elucidating the association of additive films to oil-hematite interfaces from molecular dynamics simulations. On this basis, ‘saturated’ interface models of densely packed OFMs are suggested.