Mechanochemical exfoliation of sugar-assisted boron nitride nanosheets for achieving superlubricity and wear distinction

Boron nitride nanosheets (BNNS) possess extensive potential applications across various fields. However, their limited dispersibility in liquids constrains their effectiveness as lubricating additives. In this study, a streamlined sugar-assisted mechanochemical exfoliation technique was employed to concurrently exfoliate and functionalize BNNS. This approach enabled the covalent grafting of sucrose molecules onto BNNS, enhancing their dispersion in water. The application of water containing sucrose-modified BNNS (S-BNNS) facilitated an ultralow coefficient of friction (COF = 0.001) at the Si₃N₄-Si₃N₄ interface. Additionally, using S-BNNS nanosheets as lubricating additives in water achieved superlubricity with a significant surface roughness (Ra ≤120 nm). We explored the correlation between surface roughness and superlubricity, revealing that tribological performance was enhanced by the formation of a tribofilm composed of S-BNNS and a silica layer at the interface through tribochemical reactions. The exceptional anti-wear properties and significantly reduced shear strength of S-BNNS within the tribofilm substantially contributed to achieving the ultralow COF, thus enhancing lubrication performance.