Diprotic Ammonium Succinate Ionic Liquid in Thin Film Aqueous Lubrication and in Graphene Nanolubricant

An ammonium succinate protic ionic liquid (PIL) has been used as additive in water and as base lubricant for graphene dispersions in sapphire-stainless steel lubrication. The tribological performance of a water-based lubricant containing the PIL additive di[bis(2-hydroxyethyl)ammonium] succinate (DSu) in 1 wt% proportion (Water + DSu) has been studied. Both neat DSu and Water + DSu lubricants present a high friction coefficient during the running-in period. Elimination of the running-in high friction period has been achieved with a DSu layer generated on the steel surface by evaporation of water, before the sliding begins. This DSu surface layer reduces the wear rate in two orders of magnitude with respect to full-fluid Water + DSu and to neat DSu lubricants. The high friction running-in period can also be eliminated by the addition of 0.05 wt% few-layers graphene (G) to DSu. The new (DSu + 0.05G) nanolubricant also prevents wear and surface damage on stainless steel. Surface interactions are discussed from contact angles, SEM and TEM microscopies, XPS surface analysis, and Raman microscopy results.