Segregation in mixtures of granular chains and spherical grains under vertical vibration.

We experimentally investigate segregation behaviors of binary granular mixtures consisting of granular chains and spherical grains with different interstitial media under vertical vibrations. A quantitative criterion is proposed to locate the boundaries between different vibrating phases. The water-immersed granular mixture exhibits two interesting types of segregation behaviors: chain-on-top and sandwich patterns. However, the phenomenon of sandwich segregation is absent for the air-immersed mixture. The topological differences of phase diagrams between two different environments indicate that the interstitial fluid plays an important role on the granular demixing. Additionally, the phase behaviors of mixtures for the different chain lengths show a not significant discrepancy. Finally, the vibrating thickness ratio determining the phase boundary characterizes the mixing extent of the granular bed. The estimated ratios for various chain lengths exhibit a monotonically decreasing dependence, when the vibration frequency increases.