Synergy between graphene and ionic liquid lubricant additives

Graphene (G) (0.005 wt%), the ionic liquid (IL) 1-octyl-3-methylimidazolium tetrafluoroborate (5 wt%) or a 5 wt% dispersion of 0.1 wt% graphene in IL (IL + G) have been evaluated as friction-reducing and antiwear additives of an additive-free isoparaffinic base oil (B), at room temperature, and a fully-formulated lubricant oil (FFO) at 150 °C. The best performances were found for [B+(IL + G)] and for (FFO + G), respectively. In the case of [B+(IL + G)], the presence of IL enhances the load-carrying and surface separating ability of graphene, leading to unmeasurable wear. In contrast, the lowest friction coefficient at 150 °C (0.03) is obtained for (FFO + G). Raman spectroscopy shows a carbon-rich graphene-containing layer on the wear track after lubrication with (FFO + G), which would be responsible for its outstanding tribological performance. [Display omitted] •Addition of 0.005 wt. % graphene reduces more than a 70% the friction coefficient of motor oil at 150 ºC.•The formation of graphene surface layer reduces material loss from the steel surface.•For additive-free oil, graphene dispersed in ionic liquid achieves friction reduction and prevent wear at room temperature.