Tribological Behaviour of Plasma-Functionalized Graphene as Low-Viscosity Oil Additive

The influence of plasma functionalization of multilayer graphene (MG) as an additive for low-viscosity polyolester (POE) oil in terms of dispersion stability and tribological behaviour was investigated. Pure MG and MG functionalized via N2 and NH3 plasma were analysed. The plasma functionalization significantly improved the substrate wettability and the dispersion stability of the nanofluids. The tribological behaviour of the nanofluids was investigated using a reciprocating cylinder on plane configuration. 0.05 wt% of the functionalized nanoparticles dramatically increased the scuffing resistance and significantly improved the anti-wear properties of the POE oil (over 60% wear reduction). Optical microscopy, white light interferometry, scanning electron microscopy and micro-Raman spectroscopy were used to identify the wear mechanisms. The functionalization provides a well-dispersed suspension, which contributes to the formation of a continuous and homogeneous anti-wear tribofilm. Once between the sliding surfaces, the MG improves the load-carrying capacity of the oil, avoiding the seizure of the tribolayer.