  Solids at incommensurate contact display low-friction, 'superlubric',
sliding. For graphene flakes on a graphite surface, superlubric sliding is only
temporary due to rotation of the flakes from incommensurate to commensurate
contact with the substrate. We examine this rotational channel of friction in a
prototype geometry of meso- and macroscopic solid lubrication. By molecular
dynamics simulations and theoretical arguments we find that two surfaces
lubricated by mobile, rotating graphene flakes exhibit stable superlubric
sliding as for ideally incommensurate contacts also when they are covered by
randomly oriented pinned graphene patches. For commensurate surfaces, we find a
low friction state at low temperature where incommensurate states are not
destroyed by thermal fluctuations.
