Segregation patterns in binary granular mixtures with same layer-thickness under vertical vibration

Inspired by the theoretical prediction [Phys. Rev. Lett. 86, 3423 (2001)] and the disputed experimental results [Phys. Rev. Lett. 89, 189601(2002), Phys. Rev. Lett. 90, 014302 (2003)] about the problem of granular segregation, we systematically investigate the pattern of binary granular mixtures consisting of same layer-thickness under vertical vibration. Various kinds of mixtures with different diameters and densities particles are poured into the glass cylinder that is sealed and evacuated to an air pressure less than 50 Pa to observe separation patterns. It is found that these granular mixtures behave like five kinds of segregation patterns for different driving control parameters, i.e., Brazil nut (BN), reversed Brazil nut (RBN), Mixed states, light-BN (LBN), and light-RBN (LRBN). The latter two regimes are neither purely segregated nor completely mixed states. Moreover, BN phenomenon takes place in the area of low density ratio and found to be independent of layer-thickness, while RBN is sensitive to both the layer-thickness and frequency and occurs at the large density ratio area. Our result may be helpful for the establishment of theory about the segregation and mixing of granular mixtures.