Confined disordered strictly jammed binary sphere packings

TL;DR

This study investigates how binary sphere packings confined between two planes differ from bulk packings, revealing effects of confinement on packing density, disorder, and hyperuniformity, with implications for biological and industrial applications.

Contribution

We extend the Torquato-Jiao algorithm to generate maximally random jammed packings under confinement, analyzing their structural properties across various parameters.

Findings

Confined packings show different characteristics from bulk packings due to confinement frustration.

Rattler prevalence is higher in confined packings than in bulk.

Packing fraction and disorder generally increase with confinement height H.

Abstract

Disordered jammed packings under confinement have received considerably less attention than their \textit{bulk} counterparts and yet arise in a variety of practical situations. In this work, we study binary sphere packings that are confined between two parallel hard planes, and generalize the Torquato-Jiao (TJ) sequential linear programming algorithm [Phys. Rev. E {\bf 82}, 061302 (2010)] to obtain putative maximally random jammed (MRJ) packings that are exactly isostatic with high fidelity over a large range of plane separation distances $H$, small to large sphere radius ratio $\alpha$ and small sphere relative concentration $x$. We find that packing characteristics can be substantially different from their bulk analogs, which is due to what we term "confinement frustration". Rattlers in confined packings are generally more prevalent than those in their bulk counterparts. We observe that packing fraction, rattler fraction and degree of disorder of MRJ packings generally increase with $H$, though exceptions exist. Discontinuities in the packing characteristics as $H$ varies in the vicinity of certain values of $H$ are due to associated discontinuous transitions between different jammed states. We also apply the local volume-fraction variance $\sigma_{\tau}^2(R)$ to characterize confined packings and find that these packings possess essentially the same level of hyperuniformity as their bulk counterparts. Our findings are generally relevant to confined packings that arise in biology (e.g., structural color in birds and insects) and may have implications for the creation of high-density powders and improved battery designs.