Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Physics Department, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Phys Rev E. 2017 Nov;96(5-1):052905. doi: 10.1103/PhysRevE.96.052905. Epub 2017 Nov 20.
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 small-sphere composition, f. Our simulations reveal that at high values of ratio α of large- to small-sphere radii (α≥α_{c}≈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 valued range of α above a critical value, α_{c}≈5.75. The existence of a sharp transition from small- to large-f values for α≥α_{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}(α). We argue that the critical value of finite-size asymmetry α_{c}≃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.
我们研究了粒径非对称对具有不同大球和小球组成的随机堆积双球混合物结构演化的影响。通过对堆积体的模拟来评估从大球主导混合物向小球主导混合物的转变。对于粒径的弱非对称性，堆积体的性质随着小球组成的增加而平滑变化，但不是单调变化，f。我们的模拟表明，在大球与小球半径比α（α≥α_{c}≈5.75）较高的值时，结构性质的演化，如堆积密度、被阻塞球的分数和与 f 的接触统计，表现出一些特征，表明存在一个尖锐的转变，可能是通过结构测量或其导数的不连续性。我们认为，这种行为与 Furnas 模型在无限大纵横比混合物 α→∞中预测的紧密堆积分数的奇异、组成依赖性有关，但在高于临界值α_{c}≈5.75 的有限α值范围内发生。对于α≥α_{c}，从小到大 f 值的尖锐转变的存在可以归因于在沿组成线 f_{sub}(α)被阻塞的大球的间隙内小球的亚阻塞转变。我们认为，有限尺寸非对称性的临界值α_{c}≃5.75与大球相邻四面体紧密堆积间隙之间小球接触的传递的几何判据一致，有利于被约束在不相交体积内的小球的合作亚阻塞转变。
