PEGlated graphene as nanoadditive for enhancing the tribological properties of water-based lubricants

Dispersion of Graphene in water is conducive to their practical applications as lubricating additive in water-based fluids due to their safety, low cost and environmental-friendliness. But owing to its hydrophobicity, it is difficult to achieve stable aqueous graphene suspension. Here, we use the Toluene-2,4-diisocyanate as bridging agent between hydrophilic Poly (ethylene glycol) (PEG) and ethanolamine to prepare the amino-containing PEG (PEG-NH2), followed by covalently grafting PEG-NH2 onto the surface of carboxylaed graphene (G-COOH) nanosheets to synthesize the PEGlated graphene (PEG-G) via facile amidation under mild conditions. The physical, chemical properties of product were characterized by Fourier transformed infrared spectra (FTIR), Raman spectra, X-ray photo electron spectroscopy (XPS) and so on. Transmission electron microscopy (TEM) and scanning probe microscope (SPM) were utilized to observed the morphology of G-COOH and PEG-G. The frictional properties of PEG-G as nanoadditive of water-based lubricant were characterized by UMT-3 tribometer, following with analyzes on wear surfaces by 3D laser scanning confocal microscopy. Based on the results of characterization, the PEG-G was prepared successfully and the dispersion shows superior friction-reducing and anti-wear properties owing to the formation of fluid adhesive film and carbon protective film, especially the concentration of PEG-G in water is 0.05 wt%.