Surface functionalized 2D MoO3-hBN heterostructure as friction modifiers in boundary lubrication regime

Two-dimensional (2D) layered materials, known for their low interlayer shear strength and high in-plane strength, have promising potential as lubricant additives. Studies on 2D/2D heterostructures as additives are yet to be fully explored regarding their ability to create ultra-low friction from incommensurate stacked sliding at their heterostructure interfaces. In the present work, we develop 2D MoO3-hBN heterostructures as friction modifier additives in PAO oil to focus on studying the friction reduction due to incommensurate sliding of the MoO3-hBN heterostructure when compared to their MoO3-MoO3 or hBN-hBN homo-bilayer sliding at the steel-steel sliding interface. The 2D heterostructure developed using an oleic acid-oleylamine combination shows excellent dispersion stability in PAO oil. The tribological performance of this heterostructure is investigated between the steel tribo-pairs of a four-ball tester. Mixing 0.5 mg/ml f-MoO3-hBN in PAO oil reduces the friction at the tribo-contacts by 18.4 %, lower than that of f-MoO3 or f-hBN additives in PAO oil. The observed reduction in friction can be ascribed to the sliding dynamics occurring at the incommensurate stacked interfaces of MoO3 and hBN. This study highlights the possibility of developing ultra-low friction at the tribo-pairs using 2D heterostructure additives as a promising strategy for boundary lubrication.