Treelike polymeric phosphate esters grafted onto graphene oxide and its tribological properties in polyalkylene glycol for steel/steel contact at elevated temperature

We report the first synthesis of a high-performance lubricant additive by grafting treelike polymeric phosphate esters (PPEs) onto graphene oxide (GO) nanosheets. Characterization of the PPEs modified GO (GO-PPEs) was performed by spectral (FT-IR, Raman, SEM, TEM, XPS), and thermogravimetric analysis (TGA). Performance evaluations of GO-PPEs as a high-temperature friction-reduction and anti-wear additive in polyalkylene glycols (PAG) were conducted by an Optimol SRV-IV oscillating reciprocating friction and wear tester. The results indicated that GO-PPEs possessed excellent tribological properties in PAG compared with pure GO and PPEs under the same conditions, which may be attributed to the good dispersion of GO-PPEs in PAG, and the excellent tribological properties of phosphate at elevated temperature. In addition, the wear mechanism was tentatively discussed according to the surface composition.