Diffusion-induced Horizontal Segregation Of Vertically Shaken Grain-filled Binary Mixtures

A granular system is a dissipative system which is far from equilibrium.With an energy input from external environment,granular particles spontaneously form various phenomena,such as patterns,clusters,and segregation.Granular segregation is widely applied in agriculture,industry,food and pharmaceutical processing.It has attracted intensive attention from academic society for decades.After many years of research,different mechanisms including size,density-driven,geometric shape of particles,convection,inter-particles frictions and inertia effect between particles,were presented to account for the segregation.However,there is no a unified theoretical framework for seemingly simple segregation behaviors.Nowadays,most researchers agree that one or several of these mechanisms simultaneously take effect on the segregation,each being dominant in different parameter regimes.We experimentally investigate spontaneous segregation of a monolayer binary mixture of grain-filled spheres under vertically vibration.The grain-filled spheres used in the experiment refers to hollow spheres filled with particles.A kind of grain-filled spheres is filled with large size glass beads and the another is filled with small glass beads.The filling beads are identical except for their sizes.A novel horizontal segregation was found.We quantitatively defined segregation index and plot ?-? phase diagram according to the segregation degree.We also calculated the mean square displacement(MSD)of an individual grain-filled spheres and gained a diffusion coefficient.We found that the greater the discrepancy of granular diffusion is,the better the horizontal separation effect shows.Finally,according to a theoretical model,we present that the difference of diffusion coefficient is due to the asymmetry of dissipative capacity of the filling particles.