Disclinations in vibration-induced size segregation

Abstract

Vibration segregates large disks embedded in a medium of small disks and transits structurally the arrays of disks from the loosely disordered packing to the densely ordered packing. Our experiments on a monodisperse or bidisperse medium of small disks reveal that several types of topological defects, emerging during this disordered-to-ordered transition, are an isolated 5-fold disclination, an isolated 7-fold disclination, a 5-7 pair, a quadrupole of two 5-7 pairs, a grain boundary of alternating 5- and 7-fold disclinations and a closed loop of a grain boundary. The dominant types are an isolated 5-fold disclination and a 5-7 pair. Vibration eliminates more effectively 5-7 pairs than isolated 5-fold disclinations. After sufficient vibration the resulting orientational order is quasi-long-range only in two cases, i) in a monodisperse medium and ii) in a dilute bidisperse medium vibrated at small acceleration, while translational order is always short-range. The arrangement of disks in such two cases is thus hexatic-like.