An unexplored valley of binary packing: The loose jamming state

TL;DR

This paper predicts and confirms a novel loose jamming state in binary granular packings where the packing density is lower than in mono-sized packings, challenging conventional beliefs.

Contribution

It introduces a theoretical prediction and numerical evidence for a previously unexplored loose jamming state in binary packings, expanding understanding of packing regimes.

Findings

Identification of a regime where binary packings are looser than mono-sized packings

Theoretical prediction based on hard-sphere fluid theory

Numerical validation in specific size ratio and mole fraction ranges

Abstract

We present a theoretical prediction on random close packing factor \phi_RCP^b of binary granular packings based on the hard-sphere fluid theory. An unexplored regime is unravelled, where the packing fraction \phi_RCP^b is smaller than that of the mono-sized one \phi_RCP^m, i.e., the so-called loose jamming state. This is against our common perception that binary packings should always reach a denser packing than mono-sized packings at the jamming state. Numerical evidence further supports this prediction and confirms the regime location in the size ratio and mole fraction (R_r-X_s) space, where the size ratio R_r is close to 1, and the mole fraction of the smaller sphere X_s close to 0. This extreme regime remains unreported in existing literature, yet significant for our fundamental understanding of binary packing systems.