Enhanced lubricating performance by combining proton-type ionic liquids and water-soluble Cu nanoparticles as water-based lubrication additives at the steel\steel interface

Three types of alcoholic amine proton-type ionic liquids (PILs) with varying alkyl chain lengths were successfully synthesized and utilized as lubricating additives for water-ethylene glycol (WEG) through a straightforward process. Additionally, Long-chain PIL was combined with Cu nanoparticles (Cu NPs) as a lubrication additive for WEG. It was observed that both the long-chain PIL and Cu NPs were effectively dispersed in WEG. In addition, the tribological properties and lubrication mechanisms of PILs and Cu NPs were investigated and discussed. The experimental results demonstrated that the long-chain PILs showed more significant friction reduction and anti- wear effects as water-based lubricant additives than the short-chain PILs. Meanwhile, the lubrication performance of PIL and Cu NPs mixed lubricant additive was superior to that of pure WEG and WEG containing a single additive, and it showed excellent friction reduction, anti-wear, and extreme pressure properties. The outstanding tribological properties of PILs and Cu NPs can be attributed to the synergistic effect between them, as further