Bioinspired three-dimensional and multiple adsorption effects toward high lubricity of solvent-free graphene-based nanofluid

Graphene has shown great potential in the lubrication field due to its excellent mechanical property and interlayer self-lubricating peculiarity. However, graphene is difficult to directly apply as intrinsic lubricants and its chemical inertness also restricts the further improvement of lubrication performances. Inspired by the advanced lubrication system of natural snail mucus, a solvent-free graphene-based nanofluid with three-dimensional and multiple adsorption networks was fabricated by functionalization of fluorinated graphene with highly chemical activity of C–F bonds and high functionalization density (F/C ≈ 1.0). The dendritic polyethyleneimine (PEI) and the polyacrylic acid (PAA) were grafted onto the surface of graphene in turn, which endows nanofluids with a good fluidity under room temperature. Moreover, the introduced PEI and PAA synergistically contribute the three-dimensional and multiple adsorption effects like coordination and charge interactions (Fe–N and Fe3+-COO-) on the surface of friction pairs, which enables to form the stable and tough tribofilms. Therefore, it presents a good intrinsic lubricity with a low friction coefficient of ∼0.15 without obvious run-in time. Meanwhile, because of the excellent hydrophilicity, adding even small fraction of nanofluids into water reduces vastly the friction coefficient and wear rate with about 60% and 59%, respectively.