Subjamming transition in binary sphere mixtures (original) (raw)

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 α of large to small sphere radii, (α ≥ αc ≈ 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 α → ∞ by the Furnas model, but occurring for finite values range of α above a critical value, αc ≈ 5.75. The existence of a sharp transition from small-to large-f values for α ≥ αc can be attributed to the existence of a sub-jamming transition of small spheres within the interstices of jammed large spheres along the line of compositions f sub (α). We argue that the critical value of finite size asymmetry αc ≃ 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.