Subjamming transition in binary sphere mixtures

We study the influence of particle-size asymmetry on structural evolution of randomly jammed binary sphere mixtures with varying large-sphere and 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 smallsphere composition, f. Our simulations reveal that at high values of ratio alpha of large-to small-sphere radii (alpha >= alpha(c) approximate to 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 -> infinity by the Furnas model, but occurring for finite valued range of alpha above a critical value, alpha(c) approximate to 5.75. The existence of a sharp transition from small-to large-f values for alpha >= alpha(c) can be attributed to the existence of a subjamming transition of small spheres within 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) similar or equal to 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 subjamming transition of small spheres confined within the disjoint volumes.