
Patterned Surface Contact for Macro Scale Engineering Superlubricity
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Engineering superlubricity, defined as having a coefficient of friction below 0.01, can be achieved under specific circumstances such as mismatched atomic lattices in two dimensional materials[1] and incommensurate contact in patterned surfaces[2].The EIC project SSLiP aims to bring this concept to the macro scale, enabling real world applications. Scale-up is being realized by a combination of concepts including the use of tribocolloids (micron scale colloidal particles with tribological coatings), micropatterned surfaces to reduce contact area, and surface coatings of 2D materials and carrier fluid. These are predicated on ideas around creating a dynamic network of superlubricious contacts that manages total friction through understanding of dissipation in granular systems. We present a variety of fabrication methodologies including colloidal directed assembly of microparticles and photolithography to create patterned countersurfaces. Tribocoatings are created with a range of processes including chemical vapour deposition, as well as the densification of granular nanosheet films formed from spray coating of a nanosheet dispersion. Testing is performed with macroscale contact geometries, as well as microscale tribometer contacts to understand underlying mechanisms, and is supported by numerical simulation. Baseline ball and flat on flat friction coefficients below 0.01 have been maintained over thousands of cycles for sub-millimeter contact geometries. We discuss the effect of patterning surface geometries on our ability to extend these results to larger scale areas.