Enhanced tribological performance of water-based lubricant with oleic acid-modified Fe₃O₄ and aminated SiO₂ nano additives

Water-based lubrication systems are increasingly attractive due to their environmental friendliness, cost-effectiveness, and safety merits. While oleic acid-modified magnetite nanoparticles (Fe₃O₄-OA) have demonstrated promising properties as lubricant additives in oil-based systems, their performance in water-based lubrication systems remains largely unexplored, as the Fe₃O₄-OA nanoparticles exhibit limited dispersion stability and tribological performance in aqueous environments. In this study, Fe₃O₄-OA was combined with amine-functionalized silica (SiO₂-NH₂) nanoparticles to enhance the anti-friction and anti-wear properties in water-based lubrication. Comparative tribological tests showed that adding 1 wt% Fe₃O₄-OA and 1 wt% SiO₂-NH₂ reduced the coefficient of friction by 72.4% and the wear volume by 81.7% under a 100 N load compared with pure water. Small-angle neutron scattering (SANS) analysis reveals that increasing Fe₃O₄-OA concentration led to a more extended configuration of oleic acid molecular chains, facilitating interactions with surface amine groups on SiO₂-NH₂. These interactions promote the formation of a stable and compact tribofilm through combined Lewis acid–base coordination, hydrogen bonding, and electrostatic attraction. The improved frictional performance provides insights into the rational design of high-performance, water-based lubrication systems via nanoparticle additives. © 2026 Elsevier B.V.