Lubricating performances of oil-miscible trialkylanmmonium carboxylate ionic liquids as additives in PAO at room and low temperatures

Abstract Ionic liquids (ILs) have recently been demonstrated as a promising lubricating material. However, data on ILs with splendid solubility in non-polar oil and their low-temperature lubricating performances are rarely reported. In this paper, we synthesized four novel oil-miscible protic ionic liquids (PILs) containing different fatty acid anions. They possess low pour point, good low-temperature fluidity, non-corrosiveness and higher thermostability. These PILs were selected as additives in PAO base oil, respectively, and their lubricating performances were tested using a steel ball reciprocating sliding against steel stationary disc at room and low temperatures. At room temperature (~30 ℃), [N888H]C6 with shorter alkyl chains exhibited good lubricating behaviors, both in terms of steady-state friction coefficient and wear volume. However, the lubricating performances of [N888H]OA with longer alkyl chains were relatively poor because the lubricating film formed by it is disordered. At low temperature (-20 ℃), these PIL additives produced excellent antiwear performances, while their friction-reducing properties were unobvious, attributing to the restriction of high kinematic viscosity of PAO base oil.