Reducing friction and wear inside lubricated contacts could lead to significant improvements in energy efficiency and emissions at a global level. Efforts in this direction are limited by lack of detailed fundamental understanding of the physicochemical mechanisms taking place at tribological interfaces. Molecular modelling can provide valuable insights into the atomic-scale behaviour of these systems in order to drive rational design of new lubricants and engineered surfaces that can meet current and future demands.
In this thesis, several industrially-relevant tribological systems are studied by different molecular modelling methods. Firstly, the mechanisms through which different dopants affect the water adsorption and the subsequent hydrophobicity of diamond-like carbon coatings is investigated. The interaction between these coatings and water plays a central role not only on their frictional performance, but also gives clues as to their interactions other polar molecules such as lubricant additives. Secondly, a classical interfacial force field to model the adsorption of organic friction modifier additives on iron oxide is developed and applied to molecular dynamics simulations under boundary lubrication conditions. Finally, the decomposition mechanisms of adsorbed phosphate ester antiwear additives on ferrous surfaces are investigated using reactive molecular dynamics simulations. The effects of surface chemistry and molecular structure are studied, separately for both thermal and mechanochemical decomposition. The work presented here has contributed to a more complete picture of the atomic-scale phenomena at tribological interfaces and has also helped to explain recent experimental results. The techniques developed have paved the way towards rational design of lubricant additives using in silico methods.