Victoria-Camacho Jonathan A, DeLaCruz-Araujo Ronal A, Kretzschmar Ilona, Córdova-Figueroa Ubaldo M
Department of Mechanical Engineering, University of Puerto Rico-Mayagüez, Mayagüez, PR 00681, USA.
Soft Matter. 2020 Mar 11;16(10):2460-2472. doi: 10.1039/c9sm02020a.
Anisotropic potentials in Janus colloids provide additional freedom to control particle aggregation into structures of different sizes and morphologies. In this work, we perform Brownian dynamics simulations of a dilute suspension of magnetic spherical Janus colloids with their magnetic dipole moments shifted radially towards the surface of the particle in order to gain valuable microstructural insight. Properties such as the mean cluster size, orientational ordering, and nucleation and growth are examined dynamically. Differences in the structure of clusters and in the aggregation process are observed depending on the dipolar shift (s)-the ratio between the displacement of the dipole and the particle radius-and the dipolar coupling constant (λ)-the ratio between the magnetic dipole-dipole and Brownian forces. Using these two dimensionless quantities, a structural "phase" diagram is constructed. Each phase corresponds to unique nucleation and growth behavior and orientational ordering of dipoles inside clusters. At small λ, the particles aggregate and disaggregate resulting in short-lived clusters at small s, while at high s the particles aggregate in permanent triplets (long-lived clusters). At high λ, the critical nuclei formed during the nucleation process are triplets and quadruplets with unique orientational ordering. These small clusters then serve as building blocks to form larger structures, such as single-chain, loop-like, island-like, worm-like, and antiparallel-double-chain clusters. This study shows that dipolar shifts in colloids can serve as a control parameter in applications where unique size, morphology, and aggregation kinetics of clusters are required.
Janus胶体中的各向异性势为控制粒子聚集形成不同尺寸和形态的结构提供了额外的自由度。在这项工作中，我们对磁性球形Janus胶体的稀悬浮液进行了布朗动力学模拟，其磁偶极矩沿径向朝着粒子表面移动，以便获得有价值的微观结构见解。我们动态地研究了诸如平均团簇尺寸、取向有序性以及成核和生长等性质。根据偶极位移（s）——偶极位移与粒子半径之比——以及偶极耦合常数（λ）——磁偶极-偶极力与布朗力之比，观察到团簇结构和聚集过程中的差异。利用这两个无量纲量，构建了一个结构“相”图。每个相都对应于团簇内部独特的成核和生长行为以及偶极的取向有序性。在小λ时，粒子聚集和解聚，在小s时导致短寿命团簇，而在高s时粒子聚集成永久性三聚体（长寿命团簇）。在高λ时，成核过程中形成的临界核是具有独特取向有序性的三聚体和四聚体。这些小团簇随后作为构建单元形成更大的结构，如单链、环状、岛状、蠕虫状和反平行双链团簇。这项研究表明，胶体中的偶极位移可以作为一个控制参数，应用于需要团簇具有独特尺寸、形态和聚集动力学的场合。
