Boundary Slip of Oil Molecules at MoS₂ Homojunctions Governing Superlubricity

Molybdenum disulfide (MoS₂) nanoflakes are widely used as nano-additives in oil for the excellent lubrication performance. However, the molecular mechanism of MoS₂ nanoflakes in oil governing the friction properties remains elusive. In this study, MoS₂ homojunctions were constructed by combining the fabricated MoS₂ probe and MoS₂ crystal with an atomic force microscope (AFM), and the superlubricity with an ultralow friction coefficient of approximately 0.003 at MoS₂ homojunctions was attained after the formation of a confined oil layer, exhibiting a 67% reduction of the friction coefficient in comparison to that under a nitrogen atmosphere. The boundary slip of oil molecules on the MoS₂ crystal with a small energy barrier was observed, causing the shear to occur at the interface of oil/MoS₂ crystal with an extremely low shear strength, which contributes to the achievement of superlubricity. This boundary slip of oil molecules at MoS₂ homojunctions can be extended to the macroscale for friction reduction, supplying a fundamental insight into the lubrication mechanism of MoS₂ nanoflakes in oil, which has potential applications for designing an efficient lubrication system with nano-additives.