Elasticity of soft particles and colloids near Random Close Packing

TL;DR

This paper investigates the elastic properties of soft particles and colloids near their random close packing, revealing why their shear modulus can be much smaller than the bulk modulus and providing a theoretical explanation for their elastic scaling behavior.

Contribution

It offers a new theoretical explanation for the scaling of elastic moduli in jammed particle systems, applicable to both soft and hard particles.

Findings

Shear modulus can be much smaller than bulk modulus near jamming

Theoretical scaling laws for elastic moduli are consistent with observed data

Structural analysis explains the elastic behavior of jammed packings

Abstract

Assemblies of purely repulsive and frictionless particles, such as emulsions or hard spheres, display very curious properties near their jamming transition, which occurs at the random close packing for mono-disperse spheres. Although such systems do not contain the long and cross-linked polymeric chains characterizing a rubber, they behave macroscopically in a similar way: the shear modulus $G$ can become infinitely smaller than the bulk modulus $B$. After reviewing recent theoretical results on the structure of such packing (in particular their coordination) I will propose an explanation for the observed scaling of the elastic moduli, and explain why the arguments both apply to soft and hard particles.