Superlubricity — the condition by which friction between two surfaces essentially tends to zero — has been previously observed for nanoscale sliding structures. Realizing it at the macroscale however is highly desirable for engineering applications, yet problematic due to issues with structural defects. Towards this end, a number of works have proven the beneficial effect that graphene can play in reducing friction. Now, Diana Berman et al. have demonstrated that superlubricity can be achieved at the macroscale in a dry environment by the addition of nanodiamonds between graphene flakes on a silicon substrate and a sliding diamond-like carbon interface, reporting a coefficient of friction of approximately 0.004. Analysis of the wear debris reveals that the nanodiamonds become wrapped up in the graphene flakes, forming nanoscrolls. Supporting simulations show that more of the graphene flakes scroll with time, gradually reducing the contact area between the nanoscrolls and the diamond-like carbon contact surface, allowing a superlubric state to be reached.
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Plummer, J. Sliding scrolls. Nature Mater 14, 654 (2015). https://doi.org/10.1038/nmat4344