Sub-Jamming Transition in Binary Sphere Mixtures

TL;DR

This study investigates how particle size asymmetry affects the structural evolution and jamming transition in binary sphere mixtures, revealing a critical size ratio where a sharp sub-jamming transition occurs.

Contribution

It identifies a critical size ratio (~5.75) where a sub-jamming transition emerges, linking structural behavior to geometric packing models in binary sphere mixtures.

Findings

Sharp transition in structural properties at high size ratios

Existence of a sub-jamming transition of small spheres

Critical size ratio aligns with geometric transmission criteria

Abstract

We study the influence of particle size asymmetry on structural evolution of randomly jammed binary sphere mixtures with varying large-sphere/small-sphere composition. Simulations of jammed packings are used to assess the transition from large-sphere dominant to small-sphere dominant mixtures. For weakly asymmetric particle sizes, packing properties evolve smoothly, but not monotonically, with increasing small sphere composition, $f$. Our simulations reveal that at high values of ratio $\alpha$ of large to small sphere radii, ($\alpha\geq \alpha_c \approx 5.75$) evolution of structural properties such as packing density, fraction of jammed spheres and contact statistics with $f$ exhibit features that suggest a sharp transition, either through discontinuities in structural measures or their derivatives. We argue that this behavior is related to the singular, composition dependence of close-packing fraction predicted in infinite aspect ratio mixtures $\alpha\rightarrow\infty$ by the Furnas model, but occurring for finite values range of $\alpha$ above a critical value, $\alpha_c \approx 5.75$. The existence of a sharp transition from small- to large-$f$ values for $\alpha\geq \alpha_c$ can be attributed to the existence of a {\it sub-jamming transition} of small spheres in the interstices of jammed large spheres along the line of compositions $f_{sub}(\alpha)$. We argue that the critical value of finite size asymmetry $\alpha_c \simeq 5.75$ is consistent with the geometric criterion for the transmission of small sphere contacts between neighboring tetrahedrally close packed interstices of large spheres, facilitating a cooperative sub-jamming transition of small spheres confined within the disjoint volumes.