Segregation in Vertically Vibrated Binary Granular Mixtureswith Same Size

Abstract

Segregation in vertically vibrated binary granular mixtures with samesize is studied experimentally. A new partial segregated stateis found in this system. This state exists between the completelymixed state and the pure segregated state, and has the characteristicthat the lighter particles tend to rise and form a pure layer on thetop of the system while the heavier particles and some of the lighterones stay at the bottom and form a mixed layer. The ratio of thethickness of the pure top layer and that of the whole system variescontinuously with the vibration frequency or amplitude. It is suggestedto consider the ratio as an order parameter for describing the degree ofthe segregation quantitatively. By use of the order parameter, adetailed phase diagram is obtained in Γ versus f space.Finally, the formation of the observed partial segregated stateis illustrated by the competition between the impact of momentum of theheavier particles and the stiffness of the layer composed of the mixedparticles.