Clustering-induced attraction in granular mixtures of rods and spheres

TL;DR

This study investigates how clustering enhances depletion-induced attraction between rods in a granular gas, revealing novel stable rod pairs mediated by spheres and influenced by shaking intensity.

Contribution

It introduces a new granular model showing clustering-induced attraction and stability of rod pairs, expanding understanding of depletion forces in granular systems.

Findings

Stable rod pairs increase with shaking intensity

Velocity distributions show suppressed momentum in trapped spheres

Attraction strength comparable to depletion forces

Abstract

Depletion-induced aggregation of rods enhanced by clustering is observed to produce a novel model of attractive pairs of rods separated by a line of spheres in a quasi-2D, vertically-shaken, granular gas of rods and spheres. We show that the stability of these peculiar granular aggregates increases as a function of shaking intensity. Velocity distributions of spheres inside and outside of a pair of rods trapping a line of spheres show a clear suppression of the momentum acquired by the trapped spheres. The condensed phase formed between the rods is caused by a clustering instability of the trapped spheres, enhanced by a vertical guidance produced by the confining rods. The liberated area corresponding to direct excluded-volume pairs and indirect depletion-aggregated pairs is measured as a function of time. The stability of rod pairs mediated by spheres reveals an attraction comparable in strength to the one purely induced by depletion forces.