Argonne National Laboratory,
Keywords: graphene, coatings, nanodiamond, superlubricity
Summary:Achieving superlubricity (a near zero friction) at true macroscale has been a quest for tribologists for many years because of tremendous advantages it may offer in terms of energy saving that is otherwise wasted in friction and wear. Earlier reports of structural superlubricity at nanoscale were based on structural incommensurability between sliding lattice planes in graphite  and then recently, few interesting approaches have been proposed and demonstrated to extend structural superlubricity from micro to centimeter scale [2-3]. However, maintaining continuous superlubricity at macroscale (which can be reproducibly translated into true engineering scale) has been very challenging with crystalline solids so far, since even small defect or disorder on the surface could destroy this effect. In this work, we experimentally demonstrated that superlubricity can be realized at macroscales with sliding a diamond-like carbon (DLC) surface against graphene mixed with nanodiamonds . We showed that during sliding, graphene patches wrap around nanodiamonds reducing the contact area and DLC provides a perfect incommensurate surface to achieve superlubric state for extended time periods. We performed detailed large-scale molecular dynamics simulations which closely elucidated the mesoscopic link that bridges the nanoscale mechanics and macroscopic experimental observations, thus introducing a new mechanism to explain our experimental results. Our discovery offers a direct pathway for designing smart frictionless tribological systems for practical applications of industrial interest. References: 1. Superlubricity of graphite Dienwiebel et al. Physical Review Letters, 92(12), 126101 (2004) 2. Observation of Microscale Superlubricity in Graphite Liu et al. Physical Review Letters, 108, 205503 (2012) 3. Superlubricity in centimetres-long double-walled carbon nanotubes under ambient conditions, Zhang et al. Nature Nanotechnology, 8, 912 (2013) 4. Macroscale superlubricity enabled by graphene nanoscroll formation Berman et al. Science, 348, 6239, 1118 (2015) This work was performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility under Contract No. DE-AC02-06CH11357.