Abstract
This is the first experimental study of segregation of mixtures of spherocylindrical rods of same volume and different elongations (down to the limit of spheres, where elongation is zero). When vibrated in a cylinder, we observe that short spherocylinders tend to migrate above isovolume spheres, while long spherocylinders tend to migrate to the bottom. More generally, short spherocylinders tend to migrate to the top of long spherocylinders. Moreover, the particles migrating to the bottom tend to arrange in an ordered state. We couple experiments and numerical simulations. Our discrete element model (DEM) faithfully captures the physical behavior, contrarily to previous studies made with Monte Carlo methods. We extend the study to binary mixtures of spheres and spherocylinders that have different volumes. We link these observations to the tendency of rods to orient vertically and interpret both phenomena through an extension of the void-filling mechanism.