School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
J Chem Phys. 2012 Jul 14;137(2):024905. doi: 10.1063/1.4734021.
Monodisperse polyhedral nanocrystals with O(h) (octahedral) symmetry self-assemble into various mesophases and crystal structures at intermediate and high concentrations. In this work, the effect of quenched size polydispersity on phase and jamming behavior has been studied via molecular simulations for three representative O(h) polyhedral shapes; namely, cubes, cuboctahedrons, and truncated octahedrons. Polydispersity is set by the standard deviation "δ" of an underlying Gaussian distribution of particle sizes, and is "quenched" in that it is fixed in a given uniphase sample. Quenched polydisperse states are relevant to: (i) equilibrium behavior for small enough δ when phase segregation does not occur, and (ii) actual experimental behavior for arbitrary δ when dense states are reached at a rate faster than the relaxation of slow diffusion-driven fractionation modes. Space-filling polyhedrons (cubes and truncated octahedrons) are found to be more robust with respect to the nucleation of orientational and translational order at high polydispersities compared to the non-space-filling cuboctahedron, with the former shapes exhibiting an onset of jamming behavior at a critical polydispersity δ(t) that is about twice larger than that for the latter (δ(t) ≈ 0.08). Further, the orientational ordering in cubes is found to be highly resilient to polydispersity, leading to the formation of a dense, orientationally aligned, and translationally jammed state. Overall, increasing size polydispersity enhances the range of pressures where the mesophases occur.
具有 O(h)（八面体）对称性的单分散多面纳米晶体在中间和高浓度下自组装成各种介相和晶体结构。在这项工作中，通过分子模拟研究了淬火尺寸多分散性对相和阻塞行为的影响，研究了三种代表性的 O(h) 多面体形；即，立方体、截角八面体和截角十二面体。多分散性由颗粒尺寸的基础高斯分布的标准偏差“δ”设定，并且是“淬火”的，即它在给定的单相样品中固定。淬火多分散态与以下两种情况有关：（i）当相分离不发生时，对于足够小的 δ 的平衡行为，以及（ii）当达到高密度状态的速率快于慢扩散驱动的分馏模式的弛豫时，对于任意 δ 的实际实验行为。与非空间填充的截角八面体相比，填充多面体（立方体和截角十二面体）在高多分散性下对于取向和平移有序的成核具有更强的稳健性，前者的形状在临界多分散性 δ(t) 下表现出阻塞行为的开始，后者的形状约为后者的两倍（δ(t) ≈ 0.08）。此外，发现立方体中的取向有序对多分散性具有高度的弹性，导致形成密集、取向一致和平移阻塞的状态。总的来说，增加尺寸多分散性会增加介相出现的压力范围。
