Colloidal Crystallization via Simultaneous Depletion and Electric Field Mediated Interactions

将纳米和微胶体颗粒组装成有序材料和可重构器件的能力为新兴技术（如光子晶体、超材料、隐形器件、太阳能电池等）和改进传统颗粒基材料（如陶瓷、涂料、矿物、食品、药物）提供了基础。尽管使用胶体粒子的应用范围很广，但目前在这种系统中操纵微观结构的能力在两个方面受到限制：可以获得的有序程度，以及生成有序结构所需的时间。这两个限制都是由于设计、控制和优化胶体组装过程的热力学和动力学的基本问题。胶体组装的限制因素通常不是缺乏操作胶体或制造足够复杂组件的方法，而是无法可靠地组装结构，而不会产生动力学捕获、堵塞或动态捕获的构型，这些构型是缺陷的，甚至是完全无定形的。为了解决这个问题，本项目将使用实验和建模方法来建设性地结合互补胶体组装机制的最佳方面。为了控制胶体组装，该项目将在胶体颗粒（由不吸附胶束、纳米颗粒或大分子介导）和电场介导的胶体相互作用之间采用可调的耗尽引力。目标是将这种可调的相互作用与最近开发的胶体组装动态模型相结合，以正式设计胶体结晶过程中的缺陷密度和动力学。概念性策略是利用优势，避免弱点，每个独立的方法考虑：(1)耗竭介导组装主要是一种热力学方法，其中粒子之间的相互作用决定了它们如何组装自己；所得到的结构是热力学稳定的，但容易出现动力学问题（例如点缺陷、多晶体、凝胶、玻璃），并且(2)电场介导的组装更容易动态改变胶体组装动力学，这很有吸引力，因为它提供了对随机过程的更多控制，但是一旦外部干预停止，颗粒就会简单地分解。因此，本研究将探索利用电场介导机制（控制生长或预先存在的晶体的输运、结构演化和退火）和耗尽介导组装（产生机械稳定的平衡晶体）的各种串联和并行组合来快速组装无缺陷胶体晶体的可行动力学途径。本研究将极大地促进我们对胶体相互作用的设计规则和控制参数的基本理解，从而将纳米/微粒子组装成完美有序的周期结构。在与电磁辐射波长相当的长度尺度上稳健地组装和重新配置有序材料的能力，将为生产具有独特电、磁和光学性质的多尺度“超材料”提供基础。尽管这些材料的奇异特性已经在理论上被预测出来，并在通过艰苦的微加工获得的概念验证材料中得到了证明，但现有的工艺还没有足够的可控性、可扩展性和鲁棒性，无法将这些材料用于先进的商业应用。这项研究工作的新颖之处在于使用定量测量和建模工具，使互补胶体组装方法的建设性集成能够实现无缺陷的微观结构（单靠试错发现可能会失败）。最终，提出的研究将为热运动、粒子间相互作用和外场如何决定微观有序机制的化学物理提供广泛的基础理解。除了技术成果之外，该研究项目的更广泛影响将包括从实验（如图像、视频）、模拟（如效果图、动画）和分析（如多维图）中生成丰富的视觉数据，用于各种课堂、实验室、外展和传播活动。

1234981PI: BevanThe ability to assemble nano- and micro- colloidal particles into ordered materials and reconfigurable devices provides a basis for emerging technologies (e.g. photonic crystals, meta-materials, cloaking devices, solar cells, etc.) and for improving traditional particle based materials (e.g. ceramics, coatings, minerals, foods, drugs). Despite the range of applications employing colloidal particles, current capabilities for manipulating microstructures in such systems are limited in two ways: the degree of order than can be obtained, and the time required to generate ordered structures. Both of these limitations are due to fundamental problems with designing, controlling, and optimizing the thermodynamics and kinetics of colloidal assembly processes. The limiting factor in colloidal assembly is generally not the unavailability of methods to manipulate colloids or create sufficiently complex components, but rather the inability to reliably assemble structures without producing kinetically trapped, jammed, or dynamically arrested configurations that are defect ridden or even entirely amorphous.To address this problem, this project will use experimental and modeling approaches to constructively combine the best aspects of complementary colloidal assembly mechanisms. To control colloidal assembly, this project will employ tunable depletion attraction between colloidal particles (mediated by unadsorbing micelles, nanoparticles, or macromolecules) and electric field mediated colloidal interactions. The goal is to use such tunable interactions in conjunction with recently developed dynamic models of colloidal assembly to formally engineer the defect density and kinetics in a colloidal crystallization process. The conceptual strategy is to exploit the strengths, and avoid the weaknesses, of each independent approach by considering that: (1) depletion mediated assembly is primarily a thermodynamic approach in that interactions between particles determine how they assemble themselves; the resulting structures are thermodynamically stable but are prone to kinetic problems (e.g. point defects, polycrystals, gels, glasses), and (2) electric field mediated assembly is more amenable to dynamically altering colloidal assembly kinetics, which is appealing because it provides more control over stochastic processes, but particles simply disassemble once external intervention ceases. As a result, this research will investigate viable kinetic pathways for the rapid assembly of defect free colloidal crystals using various serial and parallel combinations of electric field mediated mechanisms (to control transport, structural evolution, and annealing in growing or pre-existing crystals) and depletion mediated assembly (to produce mechanically stable equilibrium crystals).This research will significantly advance our fundamental understanding of the design rules and control parameters for tuning colloidal interactions to assemble nano-/micro- particles into perfectly ordered periodic structures. The ability to robustly assemble and reconfigure ordered materials on length scales comparable to the wavelengths of electromagnetic radiation will provides a basis for producing multi-scale "meta-materials" with unique electric, magnetic, and optical properties. Although the exotic properties of such materials have been theoretically predicted and demonstrated in proof-of-concept materials obtained via laborious microfabrication, no existing process is sufficiently controllable, scalable, and robust to enable the use of such materials in advanced commercial applications. The novelty of this research effort lies in the use of quantitative measurement and modeling tools to enable the constructive integration of complementary colloidal assembly methods to achieve defect free microscopic structures (where trial-and-error discovery alone might fail). Ultimately, the proposed research will provide broad fundamental understanding of how thermal motion, interparticle interactions, and external fields determine the chemical physics of microscopic ordering mechanisms. Beyond the technical outcomes, broader impacts of this research project will include the generation of rich visual data from experiments (e.g. images, videos), simulations (e.g. renderings, animations), and analyses (e.g. multi-dimensional plots) for use in various classroom, laboratory, outreach, and dissemination activities.