Random Close Packing of Disks and Spheres in Confined Geometries

TL;DR

This paper investigates how confinement affects the structure of random close packings of disks and spheres, revealing that walls significantly reduce packing density and induce localized structural changes.

Contribution

It provides the first systematic study of confined random close packings in 2D and 3D, introducing a model to quantify wall effects on packing density.

Findings

Confinement lowers maximum packing fractions.

Wall-induced structural effects decay within a particle diameter.

A simple model accurately predicts packing reduction due to walls.

Abstract

Studies of random close packing of spheres have advanced our knowledge about the structure of systems such as liquids, glasses, emulsions, granular media, and amorphous solids. When these systems are confined their structural properties change. To understand these changes we study random close packing in finite-sized confined systems, in both two and three dimensions. Each packing consists of a 50-50 binary mixture with particle size ratio 1.4. The presence of confining walls significantly lowers the overall maximum area fraction (or volume fraction in three dimensions). A simple model is presented which quantifies the reduction in packing due to wall-induced structure. This wall-induced structure decays rapidly away from the wall, with characteristic length scales comparable to the small particle diameter.