Approach to jamming in an air-fluidized granular bed

TL;DR

This study investigates how a bidisperse air-fluidized granular bed approaches jamming, analyzing structural and dynamical properties that resemble those in dense colloidal systems and supercooled liquids.

Contribution

It provides detailed measurements of structural and dynamical changes in a driven granular system near jamming, highlighting similarities with thermal glassy materials.

Findings

Non-Gaussian speed distributions observed

Structural measures indicate increased constraints near jamming

Vibrational density of states shows characteristic features

Abstract

Quasi-2D bidisperse amorphous systems of steel beads are fluidized by a uniform upflow of air, so that the beads roll on a horizontal plane. The short-time ballistic motion of the beads is stochastic, with non-Gaussian speed distributions and with different average kinetic energies for the two species. The approach to jamming is studied as a function of increasing bead area fraction and also as a function of decreasing air speed. The structure of the system is measured in terms of both the Voronoi tessellation and the pair distribution function. The dynamics of the system is measured in terms of both displacement statistics and the density of vibrational states. These quantities all exhibit tell-tale features as the dynamics become more constrained closer to jamming. Though the system is driven and athermal, the behavior is remarkably reminiscent of that in dense colloidal suspensions and supercooled liquids.