Investigating the Dynamics of Confined Colloidal Thin Films by a Novel Confocal Micron-Gap Rheometer

美国国家科学基金会化学与运输系统分部？微粒与多相过程项目（1415）提案号：0730813主要研究者：Zhu， Yingxi （Elaine）归属：Notre Dame提案题目：用一种新型共聚焦微米间隙流变仪研究受限胶体薄膜的动力学。该项目研究限制对两个固体表面之间的胶体悬浮液的结构和流变特性的作用。虽然该项目侧重于基础，但PI已经考虑到在许多化学和制药产品，化学加工以及各种微/纳米级设备和系统的先进功能材料中使用胶体颗粒的广泛应用。具体地说，本提案力求更深入地理解禁锢诱导的玻璃化转变和胶体薄膜动态响应的膜厚依赖性。研究小组将通过检查临界屈服应力及其结垢行为来阐明堵塞玻璃悬架的机械稳定性。该团队将进一步探索如何通过剪切和表面纹理的合理作用来流化堵塞的胶体结构。本研究的直接目标是：1)通过直接的微观观察，表征两个固体表面之间的间隙间距减小到与颗粒直径相当的尺寸时埋藏的胶体薄膜的结构；2)确定胶体薄膜在静息状态和受剪切激励影响下的动力学性质，即迁移率、弛豫过程和弛豫时间，并将其与体悬浮液的流变学联系起来；3)解决更复杂的变量，如压缩率，表面和地形组成对界面胶体层的相态和粘弹性的作用。建议的研究将集中在一个模型硬球系统？荧光标记的聚甲基丙烯酸甲酯（PMMA）微球悬浮在密度和指数匹配的非极性介质中，并被限制在两个固体表面之间：1)光滑未染色的PMMA薄层，2)有控制的地形和化学斑块的图案模板。知识价值。对受限制的胶体薄膜的玻璃化转变和界面性质以及表面性质、压缩率和剪切对复杂介质中胶体颗粒慢动力学的作用的基本理解是一个巨大的挑战。超越材料特性来解决基本的胶体物理，微米间隙流变仪与激光扫描共聚焦显微镜集成在一起，同时控制表面分离，参见？埋藏胶体粒子的三维结构及其运动，并测量对外力场的粘弹性响应。这种新颖的实验装置是PI实验室独有的。它将提供一种流变学和布朗动力学模拟研究无法提供的新方法，揭示胶体悬浮液、分子流体和许多其他复杂流体的缓慢（1秒）和长期的禁锢诱导玻璃化转变机制。这项工作的技术意义在于对玻璃化转变物理的新方法和理解。所获得的知识将用于合理的材料设计，以控制相结构，粒子间相互作用和摩擦的需求。这反过来又可能对坚韧结构陶瓷、润滑层和先进功能材料的合成、材料加工中的流化以及其他技术领域产生广泛的影响，通过控制涂漆、润滑等胶体体系的粘弹性。所获得的技术和知识将通过合理的扩展应用到更广泛的领域，例如有效的血细胞过滤和多孔介质中流体输送过程中的节能。更广泛的影响。一个基础广泛的教育/推广计划是整合在这个跨学科的研究计划。PI已经活跃于工程妇女协会（SWE）的地方分会，致力于招募和留住在许多工程学科中仍然代表性不足的女学生。PI还积极参与与圣母大学的姐妹学院圣玛丽学院的共同交流项目，圣玛丽学院是一所教育女性学生的领先私立天主教女子大学。该提案的核心是课程开发和研究指导，以加强圣母大学的材料科学和纳米技术项目。最后，该项目寻求与埃克森美孚和福特等石油和汽车行业建立强有力的联盟，以帮助学生、科学家和工程师更好地沟通和合作。

National Science Foundation - Division of Chemical &Transport Systems ? Particulate & Multiphase Processes Program (1415)Proposal Number: 0730813 Principal Investigators: Zhu, Yingxi (Elaine) Affiliation: Notre Dame Proposal Title: Investigating the Dynamics of Confined Colloidal Thin Films by a Novel Confocal Micron-Gap Rheometer This project investigates the role of confinement on the structure and rheological properties of colloidal suspensions between two solid surfaces. While this project focuses on the fundamentals, the PI has in mind broad applications of using colloidal particles in numerous chemical and pharmaceutical products, chemical processing, and advanced functional materials for various micro/nano-scale devices and systems. Specifically, this proposal strives for a deeper understanding of confinement-induced glass transition and the film-thickness dependence of dynamic responses of colloidal thin films. The research team will elucidate the mechanical stability of a jammed glassy suspension by examining the critical yield stress and its scaling behavior. The team will further explore how to fluidize jammed colloidal structures by judicious actions of shear and surface texture. The immediate objectives of this research are: 1) by direct microscopic observation, to characterize the structure of buried colloidal thin films as the gap spacing between two solid surfaces decreases down to the dimension comparable to the particle diameter; 2) to determine the dynamical properties, i.e. mobility, relaxation processes and relaxation times of colloidal thin films in the quiescent state and also under the influence of applied shear excitation and relate them to the rheology of bulk suspensions; 3) to address the roles of more complex variables, such as compression rates, surfaces and topographical compositions on phase states and viscoelastic properties of interfacial colloidal layers. The proposed research will focus on a model hard-sphere system ? fluorescence labeled poly(methyl methacrylate) (PMMA) microspheres suspended in both density and index matched non-polar media and confined between two solid surfaces treated with: 1) smooth undyed PMMA thin layers, and 2) patterned templates with controlled topographical and chemical patchiness. Intellectual Merit. The fundamental understanding of glass transition and interfacial properties of confined colloidal thin films and of the roles of surface properties, compression rates and shear on slow dynamics of colloidal particles in complex media are great challenges. Going beyond material properties to address fundamental colloidal physics, a micron-gap rheometer is integrated with a laser scanning confocal microscope to simultaneously control surface separation, ?see? 3-dimensional structures of buried colloidal particles and their motion, and measure viscoelastic responses to external forcing fields. This novel experimental setup is unique to the PI's laboratory. It will offer a new approach, unavailable to rheometric and Brownian dynamics simulation studies, to reveal the slow (1sec) and long-range mechanism of confinement-induced glass transition of colloidal suspensions, molecular fluids and many other complex fluids in general. The technical significance of this work centers on a new approach and understanding of the physics of glass transition. The knowledge gained will be employed for rational materials design to control phase structures, interparticle interaction and friction on demand. This in turn may have a broad impact on synthesis of tough structural ceramics, lubricating layers and advanced functional materials, on fluidization in materials processing, and other technical areas by controlling the viscoelasticity of colloidal systems for painting, lubrication and etc. The techniques and knowledge gained will apply by rational extension to broader areas, such as efficient blood-cell filtration and energy saving during fluid transport in porous media.Broader Impact. A broad-based education/outreach program is integrated within this interdisciplinary research program. Already active in the local chapter of the Society of Women in Engineering (SWE), the PI is committed to the recruitment and retention of female students who continue to be under-represented in many engineering disciplines. The PI also actively participates in a coexchange program with Notre Dame's sister college, St. Mary's College, a leading private woman's Catholic university in educating woman students. Central to this proposal is curriculum development and research mentoring to strengthen the materials science and nanotechnology programs at Notre Dame. Finally, this program seeks to establish a strong coalition with the oil and automotive industries such as ExxonMobil and Ford to help students, scientists and engineers communicate and work well together.