Rheological and tribological behaviour of lubricating oils containing platelet MoS₂ nanoparticles

This work concerns rheological and frictional behaviour of lubricating oils containing platelet molybdenum disulfide (MoS₂) nanoparticles (average diameter ~50 nm; single layer thickness ~3 nm). Stable nano-MoS₂ lubricants were formulated and measured for their rheological behaviour and tribological performance. Rheological experiments showed that the nano-MoS₂ oils were non-Newtonian following the Bingham plastic fluid model. The viscosity data fitted the classic Hinch–Leal (H–L) model if an agglomeration factor of 1.72 was introduced. Tribological experiments indicated that the use of MoS₂ nanoparticles could enhance significantly the tribological performance of the base lubricating oil (reduced frictional coefficient, reduced surface wear and increased stability). Scanning electron microscopy, laser confocal microscope and x-ray energy dispersive spectroscopy analyses suggested that the reduced frictional coefficient and surface wear be associated with surface patching effects. Such patching effects were shown to depend on the concentration of MoS₂ nanoparticles, and an effective patching required a concentration over approximately 1 wt%. The increased stability could be attributed to the enhanced heat transfer and lubricating oil film strength due to the presence of nanoparticles.