SOFT Group, School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom.
Departamento de Física, and Centro de Física Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal.
Phys Rev E. 2023 Mar;107(3-1):034701. doi: 10.1103/PhysRevE.107.034701.
Self-assembly of colloidal particles into predefined structures is a promising way to design inexpensive manmade materials with advanced macroscopic properties. Doping of nematic liquid crystals (LCs) with nanoparticles has a series of advantages in addressing these grand scientific and engineering challenges. It also provides a very rich soft matter platform for the discovery of unique condensed matter phases. The LC host naturally allows the realization of diverse anisotropic interparticle interactions, enriched by the spontaneous alignment of anisotropic particles due to the boundary conditions of the LC director. Here we demonstrate theoretically and experimentally that the ability of LC media to host topological defect lines can be used as a tool to probe the behavior of individual nanoparticles as well as effective interactions between them. LC defect lines irreversibly trap nanoparticles enabling controlled particle movement along the defect line with the use of a laser tweezer. Minimization of Landau-de Gennes free energy reveals a sensitivity of the ensuing effective nanoparticle interaction to the shape of the particle, surface anchoring strength, and temperature, which determine not only the strength of the interaction but also its repulsive or attractive character. Theoretical results are supported qualitatively by experimental observations. This work may pave the way toward designing controlled linear assemblies as well as one-dimensional crystals of nanoparticles such as gold nanorods or quantum dots with tunable interparticle spacing.
胶体粒子自组装成预定结构是设计具有先进宏观性能的廉价人造材料的一种很有前途的方法。向向列相液晶 (LC) 中掺杂纳米粒子在应对这些重大科学和工程挑战方面具有一系列优势。它还为发现独特的凝聚相提供了一个非常丰富的软物质平台。LC 主体自然允许实现各种各向异性的粒子间相互作用，由于 LC 指向矢的边界条件，各向异性粒子的自发排列丰富了这些相互作用。在这里，我们从理论和实验上证明了 LC 介质承载拓扑缺陷线的能力可被用作探测单个纳米粒子以及它们之间有效相互作用的行为的工具。LC 缺陷线不可逆地捕获纳米粒子，从而可以使用激光镊子沿缺陷线控制粒子运动。朗道-德加纳斯自由能的最小化揭示了随后的有效纳米粒子相互作用对粒子形状、表面锚定强度和温度的敏感性，这些因素不仅决定了相互作用的强度，还决定了相互作用的排斥或吸引特性。理论结果得到了实验观察的定性支持。这项工作可能为设计可控的线性组装以及具有可调粒子间间距的金纳米棒或量子点等纳米粒子的一维晶体铺平道路。
