Tribological synergy of carboxylic-acid-modified h-BN in polyalphaolefin under divergent contact regimes: Steel-steel versus alumina-steel

： Hexagonal boron nitride (h-BN) is an environmentally friendly lubricant that shows great potential in lubrication applications. However, there is currently a lack of research on the synergistic mechanisms of carboxylic acid-modified h-BN at different friction interfaces. In this study, the tribological mechanism of carboxylic acid-modified h-BN across various contact interfaces was investigated through experimental and molecular dynamics simulations. At the steel-steel contact, wear reductions relative to the base oil were 21.74% for unmodified h-BN, 58.94% for oleic acid (OA)-modified h-BN, and 55.80% for stearic acid (SA)-modified h-BN. At the alumina-steel contact, the corresponding wear reductions were 8.50%, 25.30%, and 23.54%, respectively. Additionally, at the alumina-steel contact, OA-modified and SA-modified h-BN reduced the coefficients of friction by 35.18% and 23.32%, respectively, compared with the base oil. Simulations revealed the adsorption mechanism of carboxylic acids: the carboxyl group anchors to the metal or oxide surfaces, while the alkyl end is compatible with the base oil. Among these, the conformational flexibility of the C=C bond in the OA molecule enables the synergistic anti-wear effect between OA and h-BN. This research outcome can guide the development of high-performance nano-lubricants suitable for multiple interfaces.