Tunable, Wide-Temperature, and Macroscale Superlubricity Enabled by Nanoscale Van Der Waals Heterojunction-to-Homojunction Transformation

X Yang and RY Li and YF Wang and JY Zhang, ADVANCED MATERIALS, 35 (2023).

DOI: 10.1002/adma.202303580

Achieving macroscale superlubricity of van der Waals (vdW) nanopowders is particularly challenging, due to the difficulty in forming ordered junctions before friction and the friction-induced complex contact restructuration among multiple nanometer-sized junctions. Here, a facile way is reported to achieve vdW nanopowder-to-heterojunction conversion by graphene edge-oxygen (GEO) incorporation. The GEO effectively weakens the out-of-plane edge-edge and in-plane plane-edge states of the vdW nanopowder, leading to a coexistent structure of nanoscale homojunctions and heterojunctions on the grinding balls. When sliding on diamond-like carbon surfaces, the ball-supported structure governs macroscale superlubricity by heterojunction-to-homojunction transformation among the countless nanoscale junctions. Furthermore, the transformation guides the tunable design of superlubricity, achieving superlubricity (& mu; & AP; 0.005) at wide ranges of load, velocity, and temperature (-200 to 300 & DEG;C). Atomistic simulations reveal the GEO-enhanced conversion of vdW nanopowder to heterojunctions and demonstrate the heterojunction-to-homojunction transformation superlubricity mechanism. The findings are of significance for the macroscopic scale-up and engineering application of structural superlubricity.

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