Halide-free PN ionic liquids surfactants as additives for enhancing tribological performance of water-based liquid

Two novel PN type ionic liquids (ILs) surfactants, N-(3-(diethoxyphosphoryl) propyl)-N,N-dimethyloctadecan-1-aminium-6-methyl-4-oxo-4H-1,2,3-oxathiazin-3-ide-2,2-dioxide and N-(3-(diethoxyphosphoryl)propyl) -N,N-dimethyl octadecan-1-aminium-2,3,4,5,6-pentahydroxyhexanoate were synthesized and investigated as a potential water-based lubricant additive. Unlike other ILs with low solubility, these ILs surfactants are stable and miscible with water-diethylene glycol. Remarkably, these additives reduce the corrosion of water on the steel and improve friction and antiwear function for the steel surface with lower friction coefficient and wear volume. Based on the results of mechanism analysis, we speculate a boundary lubricating protection film containing phosphorus and nitrogen formed on the sliding steel surfaces, achieving excellent tribological properties by a phosphorus-nitrogen synergy.