Ultrasonic-induced thickening and lubrication properties of h-BN nanosheets regulated by diurea modification

Hexagonal boron nitride (h-BN) nanosheets are widely used as key additives to enhance the performance of lubricants under harsh working conditions due to their excellent high-temperature resistance, good chemical stability, and layered structure similar to graphene. Recently, it has been found that diurea modification can endow h-BN nanosheets with unique ultrasonic-induced thickening properties, enabling their use in the formulation of ultrasonic-responsive nanogel lubricants. However, the mechanism of diureas in regulating the thickening properties and lubrication performance of h-BN nanosheets is still not well elucidated. Therefore, in this paper, h-BN nanosheets were modified with three diureas with straight-chain structures, and the effects of chain-length on the ultrasonic-induced thickening capabilities and lubricating properties in polyalphaolefin 8 (PAO8) were investigated. It was found that the thickening capabilities of modified h-BN nanosheets mainly depended on the interaction between the diureas and PAO8. Tribological tests showed that the nanogel formed by the modified h-BN nanosheets under sonication exhibited better lubrication performance than PAO8 under startup, varying speeds, and heavy load conditions. The high fluidity and high h-BN content were found to be essential for attaining optimized lubrication performance of h-BN nanogels.