A molecular dynamics "Maxwell Demon" experiment for granular mixtures

TL;DR

This study uses molecular dynamics simulations to explore how shaking a granular mixture can induce spontaneous segregation due to inelastic collisions, revealing symmetry breaking and phase transition behaviors.

Contribution

It demonstrates that inelastic collisions can cause symmetry breaking and segregation in granular mixtures under shaking, with detailed analysis of the transition and fluctuation effects.

Findings

Segregation occurs with heavy particles in denser compartments.

Density and temperature profiles show distinct segregation patterns.

Bifurcation diagrams are dominated by large fluctuations.

Abstract

We report a series of molecular dynamics simulations and investigate the possibility to separate a granular mixture of inelastic hard spheres by vigorously shaking it in a box made of two connected compartments. As its one-component counterpart, the system exhibits a ``left-right'' symmetry breaking entirely due to the inelasticity of grain-grain collisions, and triggered by increasing the number of particles. In the compartment where the density of grains is larger, we observe a partial segregation with a predominance of heavy particles. However, this compartment still has a higher density of light particles than the other one, which is light-rich. The density, granular temperature and anisotropic pressure profiles are monitored. We also discuss how to construct a relevant order parameter for this transition and show that the resulting bifurcation diagram is dominated by large fluctuations.