Unlike two liquids which reach a well-mixed state when stirred, binary powder mixtures may tend to segregate when they are shaken or in a state of flow. The raisins are always at the bottom of your box of cereal! This tendency depends among other characteristics on the particles relative size, shape and roughness.
A mixture of large glass beads and small sand grains, partially filling a horizontal tube, segregates into bands of different composition when rotated slowly. The pattern of bands evolves in time: some bands shrink and disappear, while others grow at their expense. We study the characteristics of this evolution.
Segregation
This is a tube filled with sand and beads.
When it is spun stripes appear.
The stripes coarsen, at an exponentialy decaying rate.
References
"Rotationally Induced Segregation of Granular Materials", O. Zik, D. Levine, S. G. Lipson, S. Shtrikman and J. Stavans, Phys. Rev. Lett. 73: 644 (1994).
"Avalanche Mediated Transport in a Rotated Granular Mixture", V. Frette and J. Stavans, Phys. Rev. E 56: 6981 (1997).
Mobility of a Sphere in Vibrated Granular Media,O. Zik, J. Stavans and Y. Rabin, Europhys. Lett. 17, 315 (1992).
"Self-Diffusion in Granular Flows", O. Zik and J. Stavans, Europhys. Lett. 16, 255 (1991).