Sharma Abhishek K, Escobedo Fernando A
Robert Frederick Smith School of Chemical and Biomolecular Engineering , Cornell University , Ithaca , New York 14853 , United States.
J Phys Chem B. 2018 Oct 4;122(39):9264-9273. doi: 10.1021/acs.jpcb.8b06207. Epub 2018 Sep 21.
Monte Carlo simulations are used to investigate the mechanism of the disorder-to-order phase transition for a bulk system of colloidal hard cubes. It is observed that the structure of the ordered state is foreshadowed in the disordered state through multiple spontaneously occurring ordered domains. Such domains arise due to the entropic preference for local facet alignment between particles and occur transiently and sparsely throughout the system even in the stable isotropic phase. At pressures (and degrees of supersaturation) where the isotropic phase becomes marginally metastable, a classical nucleation process is never observed; instead, the ordered domains increase in number and size, eventually reaching a critical point where they percolate the entire system and spontaneously consolidate to form the ordered phase. The critical number of particles and the per particle free-energy barrier both decrease with pressure. Using the total number of locally ordered particles as a global order parameter, it is predicted that for large systems the ordering transition would only be spontaneous above a critical pressure. Finally, a test designed to probe the ability of the system to favor a single monodomain solid from initially misaligned-ordered domains, reveals that an active interdomain zone mediates the concerted reorientation of particles.
蒙特卡罗模拟用于研究胶体硬立方体本体系统中无序到有序相变的机制。据观察，有序态的结构在无序态中通过多个自发出现的有序域得以预示。这些域的出现是由于粒子间局部晶面排列的熵偏好，即使在稳定的各向同性相中，它们也会在整个系统中短暂且稀疏地出现。在各向同性相变得略微亚稳的压力（和过饱和度）下，从未观察到经典的成核过程；相反，有序域的数量和尺寸增加，最终达到一个临界点，此时它们贯穿整个系统并自发合并形成有序相。粒子的临界数量和每个粒子的自由能垒均随压力降低。以局部有序粒子的总数作为全局序参量，预计对于大系统，有序转变仅在高于临界压力时才会自发发生。最后，一项旨在探究系统从初始排列错误的有序域中形成单一单畴固体能力的测试表明，一个活跃的域间区域介导了粒子的协同重新取向。
