The effect of molecular structure on boundary and mixed lubrication by synthetic fluids - an overview.

Current trends towards higher operating temperatures, longer oil change intervals and increasing environmental pressures are placing ever greater demands on lubricant performance, which are increasingly met by use of synthetic fluids. Synthetic,fluids differ from mineral oil in that they have generally better defined chemical structures, but also a wider range of chemical functionalities. The behaviour of synthetic fluids under boundary and mixed lubrication regimes therefore differs significantly from that of mineral oil. This paper will outline the structural features of some of the main types of commercially available synthetic fluids, including synthetic hydrocarbons, esters and polyalkylene glycols, and illustrate how these structural differences lead to different frictional properties, thin film rheology and surface reactivity.