Segregation transitions in wet granular matter
  We report the effect of interstitial fluid on the extent of segregation by imaging the pile that results after bidisperse color-coded particles are poured into a silo. Segregation is sharply reduced and preferential clumping of small particles is observed when a small volume fraction of fluid $V_f$ is added. We find that viscous forces in addition to capillary forces have an important effect on the extent of segregation $s$ and the angle of repose $\theta$. We show that the sharp initial change and the subsequent saturation in $s$ and $\theta$ occurs over similar $V_f$. We also find that a transition back to segregation can occur when the particles are completely immersed in a fluid at low viscosities. 
Azadeh Samadani, A. Kudrolli