| Graphene and ionic liquid have shown broad application prospects in the field of lubrication.Studies have shown that the functionalization of graphene using ionic liquid can greatly improve the structural integrity and dispersion stability,thereby affecting the lubricating performance of graphene in terms of interface adsorption.Research on the synergistic anti-friction performances and mechanisms of graphene and ionic liquid is of great significance for both academic and industrial applications,and it provides new ideas for the development of a new generation of green lubricant additives.In this paper,graphene/ionic liquid(G/IL)composite materials were prepared using a liquid-phase ultrasonic-assisted method.The lubricating properties and mechanisms of the lubricating oil(PAO6 base oil and shell synthetic lubricating oil)adding G/IL composite materials were investigated by using the friction tester.The main conclusions are as follows:1.The morphology and chemical structure of G/IL composite materials were characterized via scanning electron microscopy(SEM),X-ray diffraction(XRD),Raman spectra(Raman)and X-ray photoelectron spectroscopy(XPS)revealed the successful combination of graphene and ionic liquid.And G/IL composite materials have outstanding stable dispersion in base oil.2.G/IL composite materials can significantly improve the anti-friction and anti-wear properties of PAO6 base oil,and its optimal concentration is 0.04wt%.The friction coefficient and wear volume of base oil with G/IL composite materials could be successively reduced by 45%,7%,7% and 90%,56%,84%,comparing to pure PAO6 base oil(PAO6),base oil with graphene(G)and the ionic liquid(IL),respectively.In addition,the base oil containing only the G/IL composite materials(G/IL)exhibited more excellent tribological properties compared with the base oil adding multi-layer graphene and the ionic liquid mixture(IL+G)with the same mass fraction successively.Therefore,graphene and ionic liquid play a synergistic role in lubricating performance.3.The tribological performance of PAO6 base oil adding G/IL composite materials at a concentration of 0.04wt% were investigated under different load and frequency.When the load and frequency are increased,the friction coefficient also increases,and its lubrication state changes conform to the stribeck curve.When the load is 25 N and the frequency is 25 Hz,the friction reduction performance is optimal.4.Compared with pure Shell synthetic lubricating oil and Shell synthetic lubricating oil adding only graphene and only ionic liquid,Shell synthetic lubricating oil with G/IL composite materials also has significant anti-friction performance,indicating that G/IL composite materials as lubricating additives have potential application prospects.5.Raman and XPS were performed to analyze the wear surface of the steel disc,and the results showed that pinning graphene at the friction interface by ionic liquids can suppress the out-of-plane puckering effect of graphene during the rubbing process due to the ?-? interaction between graphene and ionic liquid,thereby significantly improving the anti-friction effect of graphene.The appropriate amount of graphene also promoted the tribochemical reaction of the ionic liquid at the friction interface to produce a protective film to exert the anti-friction performance.Therefore,the G/IL composite materials can be deposited on the wear surface and form ordered physical protective films,which improve the contact state of the sliding interface.They can also generate a friction chemical reaction protective film at the friction interface to reduce friction and wear. |
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