Computational investigation of the phase behavior of colloidal squares with offset magnetic dipoles
Computational investigation of the phase behavior of colloidal squares with offset magnetic dipoles
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DOI：
10.1039/d3sm00081h
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发表时间：
2023-05-19
期刊：
影响因子：
3.4
通讯作者：
Hall，Carol K.
中科院分区：
文献类型：
--
作者：
Dorsey，Matthew A.;Velev，Orlin D.;Hall，Carol K.
具有各向异性形状和相互作用的胶体颗粒表现出丰富的相行为，有可能成为具有可控性能的材料的结构基础。在本文中，我们探索了一类新粒子的自组装特征，这些粒子已被实验证明可以形成可重构结构：具有磁偶极子的微观立方体状胶体，其磁偶极子与粒子的质心横向偏移。我们使用不连续分子动力学（DMD）对二维中大量偶极方阵的动力学进行了硅模拟。我们使用了一种粗粒方法，其中偶极微立方体由一组四个硬圆结合在一起形成二维刚性正方形，两个相反的电荷嵌入正方形中以表示磁偶极子。退火，或“慢冷却”，模拟进行确定的平衡结构。偶极方阵的系统倾向于组合成两种不同类型的构象之一：单链或双链组合，每一种都有独特的结构和温度-密度平面上的相图。单链组件形成高度互连的渗透或凝胶状网络。相比之下，双链组件倾向于在高密度下形成全局排列的向列状态，尽管在所有运行中并不一致。偶极方阵系统的相行为不仅取决于系统的温度和密度，还取决于方阵中嵌入的偶极子的类型，以及系统中存在的具有相反“手性”的方阵的相对数量。
Colloidal particles with anisotropic shapes and interactions display rich phase behavior and have potential as structural bases for materials with controllable properties. In this paper, we explore the self-assembling characteristics of a new class of particles that have been shown experimentally to form reconfigurable structures: microscopic cube-shaped colloids with a magnetic dipole that is transversely offset from the particle's center of mass. We have performed in silico simulations of the dynamics of large numbers of dipolar squares in two-dimensions using discontinuous molecular dynamics (DMD). We use a coarse-grain method where the dipolar microcubes are represented by a group of four hard circles bonded together to create a rigid square in two-dimensions and two opposite charges are embedded within the square to represent a magnetic dipole. Annealing, or “slow-cooling”, simulations are conducted to determine the equilibrium structures. Systems of dipolar squares tend to assemble into one of two different types of conformations: either single- or double-stranded assemblies, each with unique structures and phase diagrams in the temperature-density plane. Single-stranded assemblies form highly interconnected percolated, or gel-like, networks. In contrast, double stranded assemblies tend to form globally-aligned nematic states at high densities, although this is not seen consistently in all runs. The phase behavior of systems of dipolar squares depends not only on the system's temperature and density, but also on the type of dipole embedded within the square and on the relative number of squares with an opposite “handedness” that are present within the system.