Tribological Performance of an Imidazolium Ionic Liquid-Functionalized SiO₂@Graphene Oxide as an Additive

A graphene oxide (GO)-wrapped SiO2 nanosphere was modified with a 1-methylimidazolium bis(salicylato)borate (MEIMBScB) ionic liquid to form a SiO2@GO@MEIMBScB nanocomposite. The SiO2@GO@MEIMBScB nanocomposite exhibited a core–shell structure, which was characterized by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy, dynamic light scattering, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The SiO2@GO@MEIMBScB nanocomposite was dispersed into poly(ethylene glycol) 400 (PEG400) as a lubricant additive, and its tribological performance was evaluated with a four-ball tribometer under 392 N at 1450 rpm for 30 min. The results showed that the SiO2@GO@MEIMBScB nanocomposite can reduce the friction coefficient by 57.27% and reduce the wear scar diameter by 16.98% at an optimized concentration. Its tribological performance was much better than the individual SiO2@GO and MEIMBScB ionic liquid and the SiO2@GO/MEIMBScB mixture. The SiO2@GO@MEIMBScB nanocomposite exhibited a synergistic effect, which was confirmed by surface analysis on a wear track. It showed that SiO2@GO@MEIMBScB can be adsorbed on the rubbing surface and form a tribo-boundary film to reduce friction and wear. A possible lubrication mechanism was proposed, which might guide the development of a novel nanolubricant additive.