Colloidal Crystallization via Simultaneous Depletion and Electric Field Mediated Interactions

1234981 PI：Bevan将纳米和微米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（例如光子晶体、超材料、隐身器件、太阳能电池等）提供了基础。以及用于改进传统的基于颗粒的材料（例如陶瓷、涂料、矿物质、食品、药物）。尽管采用胶体颗粒的应用范围，在这样的系统中操纵微结构的当前能力在两个方面受到限制：可以获得的有序度，以及生成有序结构所需的时间。这两个限制是由于设计，控制和优化胶体组装过程的热力学和动力学的基本问题。胶体组装中的限制因素通常不是操纵胶体或产生足够复杂的组分的方法的不可用性，而是不能可靠地组装结构而不产生动力学捕获、堵塞或动态停止的配置，这些配置是缺陷缠身的或甚至完全无定形的。本计画将利用实验与模拟的方法，建构性地将互补胶体组装机制的最佳方面联合收割机结合起来。为了控制胶体组装，该项目将采用胶体颗粒之间的可调耗尽吸引力（由未吸附的胶束，纳米颗粒或大分子介导）和电场介导的胶体相互作用。我们的目标是使用这种可调的相互作用，结合最近开发的动态模型的胶体组装，正式工程的缺陷密度和动力学在胶体结晶过程中。概念上的策略是利用每种独立方法的优点，避免缺点，考虑到：（1）耗尽介导的组装主要是一种热力学方法，因为粒子之间的相互作用决定了它们如何组装自己;所得到的结构是热稳定的，但是容易出现动力学问题（例如，点缺陷、多晶、凝胶、玻璃），和（2）电场介导的组装更适合于动态改变胶体组装动力学，这是有吸引力的，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，颗粒就简单地分解。因此，本研究将探讨可行的动力学途径，快速组装的缺陷免费胶体晶体使用各种串行和并行组合的电场介导的机制（控制运输、结构演化、以及在生长或预先存在的晶体中退火）和耗尽介导的组装（生产机械稳定的平衡晶体）这项研究将大大推进我们对调整胶体相互作用以组装纳米/微米材料的设计规则和控制参数的基本理解。粒子变成完美有序的周期性结构。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。尽管已经在理论上预测了这种材料的奇异性质，并且在通过费力的微制造获得的概念验证材料中得到了证明，但是没有现有的方法是足够可控的、可扩展的和稳健的，以使得能够在先进的商业应用中使用这种材料。这项研究工作的新奇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整合，以实现无缺陷的微观结构（其中试错发现可能会失败）。最终，拟议的研究将提供广泛的基本了解如何热运动，粒子间的相互作用，以及外部字段确定微观有序机制的化学物理。除了技术成果，该研究项目的更广泛影响将包括从实验（例如图像，视频），模拟（例如渲染，动画）和分析（例如多维图）中生成丰富的视觉数据，用于各种课堂，实验室，推广和传播活动。

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.