Oil-soluble deep eutectic solvent functionalized graphene oxide towards synergistic lubrication in non-polar PAO 20 lubricant

Although deep eutectic solvents (DESs) have shown excellent surface modification and lubrication properties, there have been seldom reports concerning the effect of those characters on the tribological behavior of nanoparticles as non-polar oil additives. Here, we grafted tetrabutylammonium chloride and octanol-based oil-soluble DES onto the base plane or interlayer of GO through a long aliphatic chain, chloride ion and C-N covalent functionalization, forming functionalized GO (DES/GO). The DES/GO could well disperse in a nonpolar polyalphaolefin base oil (PAO 20) to construct DES/GO hybrid PAO 20. Moreover, the friction and wear of DES/GO hybrid PAO 20 oil decreased by 35% and 41% compared with those of pure PAO 20 oil. The splendid interfacial lubrication depends on the formation of uniform, dense, and strong graphene-like tribofilm to shield the tribo-interfaces against wear. And the grafted DES on GO further participates in the tribochemical reaction to form the FexOy, FeCl2 or FeCl3 and tetraalkylammonium salt tribochemical film. The self-lubricating performance of GO and tribochemical reaction of DES together achieve a synergistic lubrication effect.