Ibuprofen-based (L-Ibu) halogen-free ionic liquids (ILs) were synthesized and evaluated as water-based lubricant additive. In contrast to the conventional ILs with fluoro-containing anions, the present L-Ibu ILs have no corrosive attack to steel and cast iron even in the water environment and exhibit extremely stable hydrolytic stability in water-ethylene glycol (W-EG) system. In addition, the Ibuprofen ILs as the water-based lubricant additives have better friction-reducing, extreme-pressure and antiwear properties than a commercial antiwear water-based lubricant additive of Hostagliss L4. The mechanism for excellent lubricating characteristics is investigated by combining electrical contact resistance measurement, X-ray photoelectron spectroscopy and interfacial adsorption behaviour by quartz crystal microbalance. The results indicate that a formed protective film on the contact surface prevents the direct contact of sliding pairs and contributes to the friction reduction and antiwear properties. More importantly, the prepared ILs provide a comparatively green alternative to the traditional halogenated ILs for the water-based lubrication application owing to halogen-, sulphur-, and phosphorus-free. So, these ILs are expected to develop into a highly efficient lubricant additive applied in water-based hydraulic fluids. [GRAPHICS] .
