DOSS^– Based QAILs: As Both Neat Lubricants and Lubricant Additives with Excellent Tribological Properties and Good Detergency

DOSS^– (dioctyl sulfosuccinate) based quaternary ammonium ionic liquids (QAILs) were synthesized and used as both neat lubricants and lubricant additives. The influence of structure on their miscibility, thermal stability, and tribological property was discussed. These QAILs are low cost as compared with conventional halogen-containing ionic liquids (ILs). They are noncorrosive and hydrolysis stable because of their halogen-free characteristics. The tribological properties of these QAILs as neat lubricants for steel/steel and steel/copper contacts are found to be better than conventional halogen-containing ILs 1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide (L-F104) and far better than traditional synthetic lubricant poly-α-olefin (PAO). Moreover, oil-soluble ILs were obtained by properly adjusting the chain length and cation asymmetry of these QAILs, which can be easily dissolved in nonpolar synthetic-oil PAO. They are found to be effective lubricant additives for improving the friction-reducing and antiwear properties of PAO. It is a great advantage as compared with conventional ILs, which have extremely low solubility in PAO and are difficult to be used as lubricant additives for this kind of base oil. Furthermore, the coking test results indicated that the synthesized QAILs have high deterging ability when used as lubricant additives for PAO. Thus, they can restrain carbonaceous deposition as well as oil sludge and varnish formation on the metal contacts during the sliding process. They can also disperse, loosen, and remove the already formed harmful substances and keep the metal contacts clean. The present work may make obvious progress toward preparing low cost, noncorrosive, and environmentally benign IL lubricants in lubrication engineering