Solvent-free ionic nanofluids based on graphene oxide-silica hybrid as high-performance lubricating additive

Abstract

Abstract Solvent-free ionic nanofluids (NFs) of graphene oxide-silica hybrid nanocores (GO@SiO2) were synthesized for the first time via functionalizing in succession the nanocores with a covalently charged corona and an ionically tethered oligomeric canopy. Being intrinsically one-component materials, GO@SiO2 NFs display a liquid-like behavior in the absence of any solvent and show excellent dispersion stability in polyethylene glycol (PEG) base oil. Adding even small amount of GO@SiO2 NFs improved dramatically the lubrication performance of PEG base oil. It was revealed that GO@SiO2 NFs played an important role in physicochemical actions on the friction interface. This work provided direct evidence that a protective tribofilm grew on the sliding surfaces when molecular species of GO@SiO2 NFs were fed continuously onto the contact zone. In particular, graphitized GO and SiO2 nanoparticles digested in the tribofilm enhanced its lubricity and robustness. It is expected that solvent-free ionic GO@SiO2 NFs open up new opportunities for developing advanced lubricating nanomaterials.