Thapar V, Hanrath T, Escobedo F A
School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
Soft Matter. 2015 Feb 28;11(8):1481-91. doi: 10.1039/c4sm02641a.
The self-assembly of hard polyhedral particles confined to a flat interface is studied using Monte Carlo simulations. The particles are pinned to the interface by restricting their movement in the direction perpendicular to it while allowing their free rotations. The six different polyhedral shapes studied in this work are selected from a family of truncated cubes defined by a truncation parameter, s, which varies from cubes (s = 0) via cuboctahedra (s = 0.5) to octahedra (s = 1). Our results suggest that shapes with small values of s show square-like behavior whereas shapes with large values of s tend to show more disc-like behavior. At an intermediate value of s = 0.4, the phase behavior of the system shows both square-like and disc-like features. The results are also compared with the phase behavior of 3D bulk polyhedra and of 2D rounded hard squares. Both comparisons reveal key similarities in the number and sequence of mesophases and solid phases observed. These insights on 2D entropic self-assembly of polyhedral particles is a first step toward understanding the self-assembly of particles at fluid-fluid interfaces, which is driven by a complex interplay of entropic and enthalpic forces. A first-order analysis of the particle-surface energies associated with a fluid-fluid interface indicates that such enthalpic interactions will be particularly important in determining particle orientation behavior at low to intermediate concentrations.
利用蒙特卡罗模拟研究了限制在平面界面上的硬多面体颗粒的自组装。通过限制颗粒在垂直于界面方向上的移动，同时允许其自由旋转，将颗粒固定在界面上。在这项工作中研究的六种不同多面体形状是从一族由截断参数s定义的截断立方体中选取的，该参数s从立方体（s = 0）经立方八面体（s = 0.5）变化到八面体（s = 1）。我们的结果表明，s值小的形状表现出类似正方形的行为，而s值大的形状则倾向于表现出更类似圆盘的行为。在s = 0.4的中间值时，系统的相行为同时表现出类似正方形和类似圆盘的特征。还将结果与三维块状多面体和二维圆形硬正方形的相行为进行了比较。这两种比较都揭示了所观察到的中间相和固相的数量及序列的关键相似性。这些关于多面体颗粒二维熵驱动自组装的见解是理解颗粒在流体 - 流体界面自组装的第一步，这种自组装是由熵力和焓力的复杂相互作用驱动的。对与流体 - 流体界面相关的颗粒 - 表面能的一阶分析表明，这种焓相互作用在确定低至中等浓度下的颗粒取向行为时将特别重要。
