Collaborative Research: Self-regulated non-equilibrium assembly of chiral colloidal clusters via electrokinetic interactions

微观物体的自主运动和运输对于维持所有生物物种的生物活性至关重要。虽然自然系统已经进化到拥有极其精密的生化马达，但合成马达的发展在复杂性和效率方面远远落后。本研究旨在为开发新型非侵入性交流电场驱动的合成微型机器人提供必要的基础知识。特别是，研究小组调查了两种类型的电场诱导的溶剂围绕微观颗粒流动之间的相互作用。这种粒子相互作用的精确控制提供了一个新的机制，货物捕获，运输，并提供了胶体微电机在实验室芯片上的设备。此外，由这些微电机形成的有组织结构是制造功能材料的优秀基石，这些功能材料具有独特的光学特性，可用于超透镜、隐形装置和分子传感。此外，该奖项还计划开发动手学习模块，以吸引科学和工程领域代表性不足的群体。本项目旨在回答胶体物理学中的一个基本问题：当受到垂直施加的交流电场时，电极附近带电介电粒子周围的电动力学流动的性质是什么？最近的一系列实验强烈地表明，经典的电流体动力流理论和诱导电荷电渗透流理论，由于只考虑来自电极的电渗透流，不足以捕捉带电介电粒子的推进和非平衡组装。相反，本项目通过互补的实验和理论研究，研究了带电粒子周围双电层的浓度极化对一种新型电动流动（浓度极化诱导电渗透）的影响。此外，利用多种类型的电动流动产生的流体动力相互作用，实现了多种胶体的自我调节非平衡组装成具有复杂对称性的均匀团簇。最后，利用微扰理论和布朗动力学模拟研究了流体动力相互作用在装配中的作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract Autonomous motion and transport of microscopic objects are essential for maintaining the bioactivities of all living species. Although natural systems have evolved to possess extremely delicate biochemical motors, the development of synthetic motors lags way behind in complexity and efficiency. This research aims to provide the fundamental knowledge necessary for developing new types of synthetic microrobots driven by non-invasive alternating-current electric fields. In particular, the research team investigates the interplay between two types of electric-field-induced solvent flow surrounding microscopic particles. Precise control of such kind of particle interactions provides a new mechanism for cargo capture, transport, and delivery by the colloidal micromotors in a lab-on-a-chip device. Moreover, the organized structures formed by those micromotors are excellent building blocks for making functional materials that exhibit exotic optical properties for applications in superlenses, cloaking devices, and molecular sensing. In addition, this award also plans to develop hands-on learning modules to engage underrepresented groups in science and engineering. Technical abstract This project aims to answer a fundamental question in colloidal physics: what is the nature of the electrokinetic flow around a charged dielectric particle near an electrode when subjected to a perpendicularly applied alternating-current electric field? A series of recent experiments strongly suggest that the classical theories on electrohydrodynamic flow and induced-charge electroosmosis flow are insufficient to capture the propulsion and non-equilibrium assembly of charged dielectric particles because it only considers the electroosmotic flow originating from the electrode. Instead, this project investigates the impact of the concentration polarization of the electric double layer around the charged particle on a new type of electrokinetic flow (the concentration-polarization-induced electroosmosis) via complementary experimental and theoretical studies. In addition, the hydrodynamic interactions originating from multiple types of electrokinetic flow are exploited to achieve the self-regulated out-of-equilibrium assembly of multiple colloids into uniform clusters with complex symmetries. Finally, perturbation theory and Brownian dynamics simulations are used to investigate the role of hydrodynamic interactions in the assembly.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.