Effect of hydroxyl functionalized ionic liquid additives on rheological and tribological properties of titanium complex grease

In this work, two kinds of hydroxyl functionalized ionic liquids (ILs) 1-butyl-3-methylimidazole salicylate [BMIM][SA] and 1-butyl-3-methylimidazole caffeate [BMIM][CA] were synthesized as additives for titanium complex grease (TCG). Two ILs can effectively improve the physicochemical properties of TCG. Among them, [BMIM][CA] significantly improves the yield stress of TCG and improved its ability to resist deformation. Tribological tests showed that both ILs improved the friction reduction and antiwear properties. And [BMIM][CA] containing two adjacent phenolic hydroxyl group performed the best. This may be because it can effectively participate in tribochemical reactions, forming a large number of organic tribochemical products, which play a key role in promoting lubrication.