Minimal Gels of Anisotropic Colloids

1232937PI：Solomon本项目将研究各向异性胶体，以此为手段将胶体凝胶的稳定性极限扩展到超低体积分数。胶体是亚微米到微米级的颗粒，弥漫在自然界以及广泛的消费品和先进材料中。各向异性胶体的例子包括胶体椭球体、Janus粒子和结合这些各向异性维度的粒子。最近，具有各向异性形状和相互作用的胶体的合成革命引入了一种新的方法来设计胶体自组装路径。同时，有强烈的科学和工程需求，需要以极低的体积分数生产胶体凝胶，因为这种凝胶可以稳定各种复杂的流体配方，所需材料最少。这一目标目前是通过球状胶体的凝胶化来实现的，这种胶体具有很强的短程成对势相互作用。该项目将应用各向异性颗粒合成和组装方面的新发展，以扩展最小凝胶化的能力，远远低于目前球形颗粒凝胶所能达到的能力。这些新方法将应用于三项研究任务。首先，通过将胶体积木从球形扩展到椭球体，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，通过在椭球胶体形状中添加片状相互作用和Janus功能，我们将探索在更低的体积分数下锁定无序微结构和弹性流变学的范围。第三，我们将使这些最小的凝胶经历大的、非线性的变形，并通过原位共聚焦显微镜和宏观流变学来探测各向异性微结构对外加流动的响应和回弹。该技术方法的独特之处包括：(I)通过在椭球胶体的尖端或中心增加片状相互作用的新方法，在基础椭球形状上增加Janus功能；(Ii)实施时间分辨双色共聚焦显微镜并结合定量图像处理，以得出最小凝胶微结构中所有各向异性胶体的位置和取向；(Iii)针对微观结构和流变学之间的关系的具体目标，因为这一关系对材料设计至关重要。除了这些技术目标，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。像本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，胶体悬浮液的软弹性流变学使各种先进材料、消费品和药物配方稳定下来。由于它们在这些行业和产品中的广泛使用，有一种非常强大的技术驱动力，即通过添加尽可能少的胶体颗粒在复杂的流体中产生类似固体的弹性。这个项目将发现控制胶体最小凝胶化的科学原理。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粒子，以及新开发的先进共聚焦显微镜成像技术。所发现的原理将立即适用于具有弹性机械性能的凝胶的设计，其体积分数极小。该项目将通过发明最小的胶体结构来增强商业复杂流体和软物质的功能能力，从而为社会带来新的机会。此外，这个项目将推进我们最近的努力，使用凝胶和剪切增稠液作为中学女孩的试验台，亲身体验科学和工程在社会中的作用之间的差异，从而推动K-12的推广。

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.