Minimal Gels of Anisotropic Colloids

1232937 PI：所罗门本项目将研究各向异性胶体，作为将胶体凝胶稳定性极限扩展到超低体积分数的一种手段。 胶体是亚微米至微米级的颗粒，遍布自然界和广泛的消费品和先进材料。 各向异性胶体的实例包括胶体椭圆体、Janus颗粒和联合收割机组合这些各向异性尺寸的颗粒。 最近，具有各向异性形状和相互作用的胶体合成的革命引入了一种设计胶体自组装路径的新方法。 与此同时，科学和工程上强烈需要以非常低的体积分数生产胶体凝胶，因为这种凝胶可以以最小的材料要求稳定广泛的复杂流体制剂。 这一目标目前是通过具有强的短程对势相互作用的球形胶体的凝胶化来实现的。 该项目将应用各向异性颗粒合成和组装的新发展，以扩展远低于目前球形颗粒凝胶的最小凝胶化能力。 这些新方法将应用于三个研究任务。 首先，通过将胶体构建块从球形扩展到椭球形，我们将发现最小凝胶化条件可以扩展到超低胶体体积分数的程度。 其次，通过添加补丁的相互作用和Janus功能的椭球胶体形状，我们将探索范围锁定在无序的微观结构和弹性流变学在更低的体积分数。 第三，我们将这些最小的凝胶大，非线性变形，并探测原位共聚焦显微镜和宏观流变学的各向异性微结构的响应和弹性施加流。 该技术方法的独特元素包括：（i）通过新方法将Janus功能添加到基础椭球形状，该新方法在椭球胶体的尖端或中心添加斑块相互作用;（ii）实施时间分辨双色共聚焦显微镜与定量图像处理相结合，以产生最小凝胶微结构中所有各向异性胶体的位置和取向;（iii）由于微观结构和流变学之间的关系对于材料设计的关键性质，因此特别针对这种关系。 除了这些技术目标之外，该项目还将在研究生教育方面取得成果，并将K-12推广到中学女生群体。该项目中研究的胶体颗粒悬浮液是一种独特的物质形式，因为它可以自组装成具有有用的机械和光学特性的平衡相。当胶体悬浮液转变为凝胶时，其软弹性流变特性可稳定各种先进材料、消费品和药物配方。 由于它们在这些行业和产品中的广泛使用，通过添加尽可能少数量的胶体颗粒，在复杂流体中产生类似固体的弹性是一个非常强大的技术驱动力。该项目将发现控制这种最小胶体凝胶化的科学原理。 为了实现这一目标，它将创造性地利用最近合成的具有独特定制的相互作用和形状的颗粒，以及新开发的先进的共聚焦显微镜成像技术。 发现的原则将立即适用于设计的凝胶弹性机械性能在极小的体积分数。 该项目将通过发明最小的胶体结构来提高商业复杂流体和软物质的功能能力，从而为社会利益带来新的机会。 此外，该项目将推进K-12推广，推进我们最近的努力，使用凝胶和剪切增稠流体作为中学女生的试验台，亲身体验科学和工程在社会中的作用之间的差异。

1232937PI: SolomonThis project will investigate anisotropic colloids as a means to extend the limits of stability of colloidal gels to ultra-low volume fractions. Colloids are submicron to micron scale particles that pervade both the natural world and a broad range of consumer products and advanced materials. Examples of anisotropic colloids include colloidal ellipsoids, Janus particles, and particles that combine these anisotropy dimensions. Recently, a revolution in the synthesis of colloids with anisotropic shapes and interactions has introduced a new means to design pathways for colloidal self-assembly. At the same time, there is a strong scientific and engineering need to produce gels of colloids at very low volume fractions, because such gels could stabilize a broad range of complex fluid formulations with minimal material requirements. This aim is currently accomplished by means of the gelation of spherical colloids with strong, short-range pair potential interactions. This project will apply new developments in anisotropic particle synthesis and assembly to extend the capabilities of minimal gelation far below that currently possible with spherical particle gels. These new methods will be applied to three research tasks. First, by extending the colloidal building block from spherical to ellipsoidal shape, we will discover the degree to which minimal gelation conditions can be extended to ultra-low colloid volume fractions. Second, by adding patchy interactions and Janus functionality to the ellipsoidal colloidal shape, we will explore the scope to lock in disordered microstructure and elastic rheology at even lower volume fractions. Third, we will subject these minimal gels to large, non-linear deformations, and probe by in situ confocal microscopy and macroscopic rheology the response and resilience of the anisotropic microstructure to imposed flow. Unique elements of the technical approach include: (i) addition of Janus functionality to the base ellipsoidal shape by new methods that add patchy interactions at either the tips, or at the center, of the ellipsoidal colloids; (ii) implementation of time-resolved two-color confocal microscopy combined with quantitative image processing to yield the position and orientation of all anisotropic colloids in the minimal gel microstructure; (iii) specific targeting of the relationship between microstructure and rheology because of the critical nature of this relationship for material design. In addition to these technical aims, the project will achieve outcomes in graduate student education, as well as K-12 outreach to groups of middle school girls.Colloidal particle suspensions such as studied in this project are a unique form of matter because then can self-assemble into equilibrium phases with useful mechanical and optical properties. A broad range of advanced materials, consumer products and pharmaceutical formulations are stabilized by the soft elastic rheology of colloidal suspensions when they are transformed into gels. Because of their widespread use in these industries and products, there is a very strong technological driver to generate solid-like elasticity in complex fluids by adding the minimum possible number of colloidal particles. This project will discover scientific principles governing such minimal gelation of colloids. To accomplish this aim, it will make creative use of recently synthesized particles with uniquely tailored interactions and shape as well as new developed advanced imaging techniques in confocal microscopy. The principles discovered will be immediately applicable to the design of gels with elastic mechanical properties at vanishingly small volume fractions. This project will yield new opportunities for societal gain through invention of minimal colloidal structures that enhance the functional capabilities of commercial complex fluids and soft matter. In addition, this project will advance K-12 outreach by moving forward our recent efforts to use gels and shear thickening fluids as a test bed for middle school girls to experience first-hand the difference between the roles of science and of engineering in society.