Clustering-Induced Attraction in Granular Mixtures of Rods and Spheres.

Gustavo M Rodríguez-Liñán,Gabriel Pérez-Ángel,Yuri Nahmad-Molinari

doi:10.1371/journal.pone.0156153

Gustavo M Rodríguez-Liñán, Gabriel Pérez-Ángel + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0156153

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Journal: PloS one	Publication Date: May 24, 2016
Citations: 23	License type: CC BY 4.0

Affiliation: Autonomous University of San Luis Potosí

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.

Highlights

Depletion forces, known as excluded-volume forces, were first described in Brownian systems by Oosawa and Asakura in 1954 [1]
The system was vertically shaken by a modal shaker fed with a sinusoidal signal of frequency ν = 60 Hz and amplitude A = 0.17 mm (dimensionless acceleration, Γ = A(2πν)2/g = 2.4, in most experiments, except where otherwise indicated)
The two new phases are constituted by a gas of spheres with just few rods diluted in it and several islands of aggregates of parallel rods

Summary

Introduction

Depletion forces, known as excluded-volume forces, were first described in Brownian systems by Oosawa and Asakura in 1954 [1] They developed a theory to describe the attraction between large particles, due to depletion of small particles in the gap between the large ones. Since fluctuations drive the system to explore the entropy landscape, the system undergoes a segregation in size or shape. This segregation produces closely packed phases of those particles capable to liberate more volume when jointed together, creating more roaming space available to those of smaller size, which remain in a fluid phase

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