Mixing and Segregation

Abstract

Liquids have a well-known predisposition for miscibility.¹ Dry granular materials, by contrast, are notorious for being difficult to mix homogeneously.² Two granular materials differing by their density, shape, size, or even by their micromechanical properties (such as coefficient of elastic restitution and friction), exhibit a distinct propensity for segregation. This phenomenon is a fundamental property of the granular state and an unending source of frustration in industry. Whenever a mixture undergoes a flow, a vibration, or a shearing action, the components tend to separate partially or completely, depending on the circumstances. By analogy with chemical reactions, we may say that under the influence of various stimuli a granular mixture inexorably tends to self-organize so as to locally reconstruct clusters of identical particles.