Colloidal suspension of graphene oxide in ionic liquid as lubricant

In this paper, we successfully prepared stable colloidal suspensions of chemically modified graphene oxide (MGO) in hydrophobic ionic liquid (IL) as a lubricant. The graphene oxide (GO) sheets were synthesized from natural graphite by modified Hummers method. To achieve stable dispersion, a surfactant containing ionic liquid unit with carboxylic acid group was synthesized and covalently grafted on GO sheets surfaces. The stability of the MGO/IL colloid was attributed to the high affinity of the surfactant, which might provide sufficient steric and electrostatic repulsions. Tribological results showed that the lubrication property of MGO/IL nanofluids has been improved significantly compared with neat IL. In addition, the lubricating effect is connected with the concentration of the MGO in IL. At the low concentration, the lubricity is ineffective. While at high concentration, the MGO sheets aggregate and the characteristic of interlayer sliding of MGO is no more active. The nanofluids with moderate MGO concentration exhibit good performance both in friction and wear resistance.