Analysis of Chain Matching between Organic Additives and Base Oils Using Molecular Dynamics Simulation

Organic friction modifiers (OFMs) play a key role in decreasing the friction between two solid contacts. OFM additive molecules are composed of alkyl chains with polar groups at the end. The metal surface and the molecules form a self-assembled monolayer (SAM). The concept of "chain matching" is known in the context of boundary lubrication; a good load-carrying capacity of an OFM film is achieved when the chain lengths of the fatty acid additives and the base oil are equal. Although this idea is supported by experiments, the precise mechanism at the molecular level has yet to be understood. In this study, an all-atom MD simulation was performed to investigate the precise mechanism of chain matching. We observed that when the chain length of the fatty acid additives matches that of the base oil, and both molecules are linear in shape, the packing is closest and the system is most energetically stable, indicating the formation of a strong membrane. Our findings contribute to a better understanding of the structural and thermodynamic factors that govern OFM and base oil compatibility.