Tribological performance of fatty acid ammonium ionic liquids as anti-wear additives in water-based fluids

In this study, we synthesized eight water-soluble ionic liquids (ILs) and investigated their tribological performance as additives in water-diethylene glycol (WDG) base fluids. The results of the tribological test suggested that these ILs additives demonstrate promising capabilities in friction reduction and anti-wear for water lubricated contacts. The ILs with the longest carboxylic chain length, namely C 10 MIPA and C 10 DIPA in this work, displayed superior tribological performances. Observations on the abraded surfaces showed that the IL forms a monolayer adsorption through self-assembly, and upon rubbing it creates a continuous and stable tribo-film with an uneven thickness of 30 - 60 nm through tribo-chemical reactions. The tribo-film mainly consists of iron oxides. The proposed lubrication mechanisms include adsorbed film and formed tribo-films, which work effectively to reduce the shear stress and thus sliding friction.