A novel approach to use some fatty acid based ionic liquids and reduced graphene oxide as lubricant additives

Reduced graphene oxide (rGO) has many advanced characteristics such as thermal and electric conductivity, layered structure and its layers can easy separate when sliding on each other. Therefore, it is very suitable for using as a lubricant additive. In this work rGO and eight ionic liquids triethyl ammonium oleate ([TEA][Oletate]), octyl ammonium oleate ([OcA][Oletate]), trialkyl methyl ammonium oleate (Alkyl: C8H17 and C10H23) ([Aliquat][Oletate]), octyl methyl imidazolium oleate ([OMIM][Oleate]), octyl methyl imidazolium stearate ([OMIM][Stearate], octyl methyl imidazolium stearate ([OMIM][Stearate]), Octyl methyl imidazolium carboxylate (fatty acid separated from coconut oil) ([OMIM][CO]), Octyl methyl imidazolium carboxylate (fatty acid separated from rubber seed oil) [OMIM][RSO]), Octyl methyl imidazolium carboxylate (fatty acid separated from waste oil) ([OMIM][WO]) with different cationic and anionic structures were used as friction-reducing additives for lubricants. The role of ionic liquids in stabilization rGO in lubricants was investigated. In addition, influence of ionic liquid structures on stabilization of rGO in lubricants was also evaluated. The friction moment was reduced by 73%-63% compared to 58% when rGO was added. Among ionic liquids with the same anion [Oleate], the ionic liquid from cation [OMIM] leaded to the most stable additive system in lubricant and the highest friction-reducing ability, followed by [OcA], [Aliquat] and [TEA]. Among ionic liquids with the same cation [OMIM], the stability and friction-reducing ability of ionic liquids followed the order of anion: [Oleate] > [RSO] > [WO] > [Stearate] > [CO].