Heterogeneous structure of granular aggregates with capillary interactions

TL;DR

This study examines the complex spatial structure of cohesive granular materials with capillary interactions, revealing heterogeneity and short-range order that differ from purely steric systems, across varying densities.

Contribution

It provides new insights into the heterogeneity and order in capillary-bridged granular systems as a function of packing density.

Findings

Exponential tails in free area distributions indicate heterogeneity at low densities.

Presence of short-range order even at low and intermediate densities.

Transition from exponential to Gamma distribution with increasing area fraction.

Abstract

We investigate the spatial structure of cohesive granular matter with spheres floating at an air-liquid interface that form disordered close packings with pores in between. The interface is slowly lowered in a conical container to uniformly compress and study the system as a function of area fraction $\phi$. We find that the free area distributions associated with Voronoi cells show significant exponential tails indicating greater heterogeneity compared with random distributions at low $\phi$ with a crossover towards a $\Gamma$-distribution as $\phi$ is increased. Further, we find significant short range order as measured by the radial correlation function and the orientational order parameter even at low and intermediate $\phi$, which is absent when particles interact only sterically.