Structure Formation, Rheology and Internal Stress Dynamics in Shear Thickening Attractive Colloidal System

本课题以复杂流体流变学为核心，开展3年综合研究、教学和推广工作。许多努力已经投入到了解颗粒负载流体的流动行为，这些材料在工业中普遍存在，是一个强大的动机。最近对凝胶形成的胶体系统中剪切增厚的观察提供了一个机会，有助于对这类重要材料的流变学的基本理解。科学目标提出的工作旨在回答有关观察到的剪切增厚的关键问题，并探索剪切增厚凝胶所显示的几个定性新现象。本提案详细描述了(1)这些材料剪切增厚的表征，(2)稳态内应力动力学的研究，以及(3)有序各向异性微观结构在这些胶体凝胶剪切变形中的演化研究。对排斥性和硬球系统中的剪切增厚给予了极大的关注。相比之下，在工业应用的大部分絮凝体系中，剪切增稠既没有预测也没有探索。提出的研究解决了这一空白，并将阐明吸引体系中剪切增厚的起源，以及对相互作用强度和体积分数的依赖。它将构成软材料中从液体到凝胶状态的系统淬火所导致的应力的短时间和长时间动力学的第一个定量研究。最后，它将提供一个新的视角，以无与伦比的细节，在流动下的复杂流体中形成各向异性涡度排列的聚集体。更广泛的impact1。气相颗粒是一种商品材料，销售额以数百万吨计，应用于各种配方和产品中。正是由于这个原因，填充牛顿流体和粘弹性流体的流变学是一个活跃的研究领域，工业界和学术界之间的科学交流是常见的。PI与Cabot公司保持着关系，他们的人员经常参加当地复杂流体社区的会议，促进了进一步的互动。在流变仪的设计和操作方面也与业界进行了技术交流。教育和外展PI是一位对教育和外展有浓厚兴趣的新教员。本项目将积极寻求代表性不足的群体参与三个本科研究项目。研究生将获得复杂流体的广泛实验背景，并通过教学、本科生指导和当地外展活动参与教育。作为耶鲁大学复杂流体/软材料研究的一部分，PI将在复杂流体流变学模块中开发包含该项目主题的课程。研究结果将在一个互动网站上公布，并将定期在新英格兰区域复杂流体工作组（NECF）的季度会议上以及在国家会议上提出。

CBET-0828905OsujiThis proposal outlines a 3-year plan of integrated research, teaching and outreach centered on complex fluid rheology. Much effort has been devoted to understanding the flow behavior of particulate laden fluids, with the underlying ubiquity of these materials in industry a strong motivator. The recent observation of shear thickening in gel forming colloidal systems presents an opportunity to contribute to the fundamental understanding of the rheology of this important class of materials.A. Scientific objectivesThe proposed work is directed towards answering key questions regarding the observed shear thickening, and to exploring several qualitatively new phenomena displayed by shear thickened gels. This proposal describes a detailed plan for (1) the characterization of shear thickening in these materials, (2) the study of internal stress dynamics in stationary states and (3) the study of the evolution of ordered anisotropic microstructures on shear deformation of such colloidal gels.B. Intellectual meritSignificant attention has been given to shear thickening in repulsive and hard sphere systems. By contrast, in flocculating systems, which constitute the majority of industrial applications, shear thickening has neither been predicted nor explored. The proposed study addresses this gap and will elucidate the origin of shear thickening in attractive systems as well as the dependence on interaction strength and volume fraction. It will constitute the first quantitative study of short and long timescale dynamics of stresses that result on system quenches from the liquid to the gel state in soft materials. Finally, it will provide a new look, with unparalleled detail, at the formation of anisotropic vorticity-aligned aggregates in a complex fluid under flow.C. Broader impact1. Technical impactFumed particles are commodity materials with sales measured in millions of tonnes and applications in all manner of formulations and products. The rheology of filled Newtonian and viscoelastic fluids is an active research area for exactly this reason, and scientific exchange between industry and academia is common. The PI maintains a relationship with Cabot Corp., and their personnel often attend meetings of the local complex fluids community, facilitating further interactions. There are also technical exchanges with industry concerning rheometer design and operation.2. Education and OutreachThe PI is a new faculty member with a strong interest in education and outreach. This project will actively seek the participation of underrepresented groups for three undergraduate research projects. Graduate students will gain a broad experimental background in complex fluids and be involved in education through teaching, mentorships of undergraduates and local outreach events. As part of a broader thrust in complex fluids/soft materials research at Yale, the PI will develop coursework incorporating themes from the project in a module on complex fluid rheology. Results will be published on an interactive website and will be regularly presented at the quarterly meetings of the regional New England Complex Fluids Workgroup (NECF) as well as at national meetings.