A Multi-scale Interfacial Investigation of Organic Friction Modifiers in Hydrocarbon

To link molecular characteristics and lubrication performance of Organic Friction Modifiers (OFMs), a multi-scale study was carried out to investigate the effects of functional groups and solvents on the tribological properties of two model OFMs, namely palmitic acid and pentadecylamine. It was observed that the solvent composition has a profound effect on the surface adsorption and the interfacial adhesion force of the OFMs, showing vastly different values of adsorption kinetics and surface coverage. It must be highlighted that the presence of water within the hydrocarbon has a considerable impact on the lubrication performance of OFMs. We were able to quantitatively correlate the molecular properties such as binding force and adsorption kinetics of the OFM with their macroscopic testing results satisfactorily, suggesting that the static Coefficient of Friction (COF) is governed by the properties of the film formed in a thermodynamic equilibrium, whilst the dynamic COF is related to the interfacial forces at the surface during sliding, and finally the wear on the solid surface is related to ability of the OFMs to rapidly re-adsorb on the solid substrate once removed.