Toward theories of friction and adhesion on quasicrystals

► We review theories of low friction and adhesion at quasicrystal surfaces. ► Low adhesion may be explained by low density of states at the Fermi energy. ► Geometric, electronic, and phononic explanations have been proposed. ► Current theories of quasicrystal friction remain incomplete. It has long been known that quasicrystal surfaces show low sliding friction and adhesion, features that have led to practical applications, notably in cookware. Several mechanisms have been proposed for how quasiperiodicity might result in low friction and low adhesion. These include mechanical characteristics (stiffness and hardness), electronic properties, phonon propagation, surface topography at atomic length scales, and relatively irrational spacings between the atoms of the two sliding surfaces (“superlubricity”). Recent work by Park et al. finds an eightfold anisotropy in the coefficient of sliding friction between a decagonal quasicrystal surface and a passivated probe. This giant anisotropy epitomizes in a single experiment the difference between periodicity and aperiodicity, yet theoretical explanations of the effect remain controversial.