Synergisms and antagonisms between MoS2 nanotubes and representative oil additives under various contact conditions

MoS2 nanotubes are known to enhance the tribological properties of lubricants thanks to support friction-reducing and anti-wear properties. However, in fully-formulated lubricants particularly for steel elements, other properties such as oxidation and corrosion protection are also necessary to provide a comprehensive lubricating performance and protection against oil degradation. As a consequence, the coexistence of MoS2 nanotubes with other oil additives is unavoidable in immediate future lubrication technologies. This study investigates the influence of representative oil additives such as anti-wear (AW), extreme pressure (EP), detergents and dispersants on the rheological and tribological performance of lubricant mixtures containing MoS2 nanotubes (NTs). The results obtained provide a wide overview on which of the current commonly used oil additives have a place in future nanolubricant formulations and which additives need to be reconsidered. In general, the synergy between the oil additives and the MoS2 nanotubes strongly depends on the contact conditions. The reason lies in the interaction mechanisms between the MoS2 nanotubes and the lubricated surfaces under the presence of the supplementary additive. MoS2 have an excellent synergy with AW additives under mixed rolling/sliding conditions due to the exfoliation of MoS2 platelets on top of the AW tribofilm. Under reciprocating sliding, the interaction between the MoS2 nanotubes and dispersant leads to higher antagonisms. Under extreme pressure unidirectional sliding, their synergy is better with S containing EP additives.