Hard convex lens-shaped particles: Characterization of dense disordered packings

TL;DR

This paper investigates dense disordered packings of hard convex lens-shaped particles, revealing their optimal aspect ratio for maximum random jammed packing density and analyzing structural properties during packing formation.

Contribution

It introduces a Monte Carlo method to generate and analyze disordered packings of optimal lens-shaped particles, highlighting their structural characteristics and packing efficiency.

Findings

Maximum random jammed packing fraction of ~0.73 for optimal lenses

MRJ state is denser, more disordered, and rattler-free compared to hard spheres

Structural descriptors increase with contact number during packing formation

Abstract

Among the family of hard convex lens-shaped particles (lenses), the one with aspect ratio equal to 2/3 is `optimal' in the sense that the maximally random jammed (MRJ) packings of such lenses achieve the highest packing fraction $\phi_{\rm MRJ} \simeq 0.73$. This value is only a few percent lower than $\phi_{\rm DKP} = 0.76210\dots$, the packing fraction of the corresponding densest-known crystalline (degenerate) packings. By exploiting the appreciably reduced propensity that a system of such optimal lenses has to positionally and orientationally order, disordered packings of them are progressively generated by a Monte Carlo method-based procedure from the dilute equilibrium isotropic fluid phase to the dense nonequilibrium MRJ state. This allows one to closely monitor how the (micro)structure of these packings changes in the process of formation of the MRJ state. The gradual changes undergone by the many structural descriptors calculated can coherently and consistently be traced back to the gradual increase in contacts between the hard particles until the isostatic mean value of 10 contact neighbors per lens is reached at the effectively hyperuniform MRJ state. Compared to the MRJ state of hard spheres, the MRJ state of such optimal lenses is denser (less porous), more disordered, and rattler-free. This set of characteristics makes them good glass formers. It is possible that this conclusion may also hold for other hard convex uniaxial particles with a correspondingly similar aspect ratio, be they oblate or prolate, and that, by using suitable biaxial variants of them, that set of characteristics might further improve.