Tribological behavior at electronic scales for an oil-soluble ionic liquid with extremely low effective addition and highly load bearing capacity

The various forms of friction and wear present in mechanical systems consume a huge amount of the world's energy sources. Ionic liquids (ILs) have drawn great attention as emerging lubricant materials and currently increasing efforts to drive their commercialization and engineering. Herein, one oil-soluble IL lubricant additive, 2-N-undecylimidazolium bis(2-ethylhexyl) phosphate ([C₁₁-IM][DEHP]), has been prepared by “bottom-up” structural design. Compared to the commercially available lubricant additive zinc dialkyl dithiophosphates (ZDDPs) and existing oil-soluble ILs, [C₁₁-IM][DEHP] shows significantly superior lubrication performance even at high normal loads (400 N). Its minimum effective concentration (0.1 wt%) is at least tenfold smaller than conventional additives. This extremely low effective concentration is vital to lower the total phosphorus content in the lubricating compounds for environmental protection and cost reduction. Furthermore, the lubrication mechanism was studied in detail by examining the electron transfer at the frictional interface and tribofilm analysis, which further reveal the lubrication nature at electronic scales for ILs.