Issue 30, 2023

Structure of jammed ellipse packings with a wide range of aspect ratios

Abstract

Motivated in part by the recent observation of liquid glass in suspensions of ellipsoidal colloids, we examine the structure of jammed two-dimensional ellipse packings over a much wider range of particle aspect ratios (α, the ratio of the major and minor axis lengths) than has been previously attempted. We determine the jamming densities ϕJ(α) to high precision, and find empirical analytic formulae that predict ϕJ(α) to within less than 0.1% for all 1≤α≤10, for three different particle dispersities. Then we explore how these packings’ local structural order varies with α. We find that the densest packings possess unusually-well-defined nearest-neighbor shells, including both a higher fraction fZ=6 of particles with exactly six contacts and a previously-unreported short-range order marked by “kinetically suppressed” regions in their positional–orientational pair correlation function g(rθ). We also show that the previously-reported approach to isostaticity (coordination number ZJZiso ≡ 6) with increasing α is interrupted and then reversed as local nematic order increases: ZJ(α) drops towards 4 as ellipses are more often trapped by contacts with a parallel-oriented neighbor on either side and a perpendicularly-oriented neighbor on either end. Finally we show that ϕJ/ϕs (where ϕs is the saturated RSA packing density) is nearly α-independent for systems that do not develop substantial local hexatic or nematic order during compression.

Graphical abstract: Structure of jammed ellipse packings with a wide range of aspect ratios

Article information

Article type
Paper
Submitted
31 May 2023
Accepted
07 Jul 2023
First published
10 Jul 2023

Soft Matter, 2023,19, 5701-5710

Structure of jammed ellipse packings with a wide range of aspect ratios

S. Rocks and R. S. Hoy, Soft Matter, 2023, 19, 5701 DOI: 10.1039/D3SM00705G

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