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 (Fe 3 O 4 -OA) have demonstrated promising properties as lubricant additives in oil-based systems, their performance in water-based lubrication systems remains largely unexplored, as the Fe 3 O 4 -OA nanoparticles exhibit limited dispersion stability and tribological performance in aqueous environments. In this study, Fe 3 O 4 -OA was combined with amine-functionalized silica (SiO 2 -NH 2 ) nanoparticles to enhance the anti-friction and anti-wear properties in water-based lubrication. Comparative tribological tests showed that adding 1 wt% Fe 3 O 4 -OA and 1 wt% SiO 2 -NH 2 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 Fe 3 O 4 -OA concentration led to a more extended configuration of oleic acid molecular chains, facilitating interactions with surface amine groups on SiO 2 -NH 2 . 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.