Solvent-free graphene liquids: Promising candidates for lubricants without the base oil.

Reduced graphene oxide modified by hyperbranched polyamine-ester (RGO-HBPE) liquids was successfully fabricated through the surface chemical engineering and tested for serving as a solvent-free novel lubricant. Structural characterization, dispersibility and rheology behavior of the lubricant and the related frication performance on steel plate were investigated thoroughly. The results manifest that the RGO-HBPE exhibited good dispersity in distilled water and liquid behavior without any solvent at ambient temperature. And this RGO-HBPE liquids could be directly introduced onto the surface of steel plate as lubricants without any additional base oil. Tribological results and the proposed lubricating mechanism of RGO-HBPE imply that the fluidity of RGO-HBPE is favorable for lubrication and is crucial to reduce the friction coefficient. The spontaneous flow of RGO-HBPE provide a spreading effect to form the lubricating film. The specific spreading effect of RGO-HBPE and the synergistic lubricating effect between HBPE and graphene demonstrate that RGO-HBPE could be directly used as promising candidates for lubricants in nowadays moving machines.