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

国家科学基金会--化学与运输系统部门？颗粒和安培多相过程计划(1415年)建议编号：0730813主要研究人员：朱英熙(伊莱恩)隶属：圣母大学建议标题：用新型共焦微米间隙流变仪研究受限胶体薄膜的动力学本项目研究限制对两个固体表面之间胶体悬浮液的结构和流变性的作用。虽然这个项目关注的是基本原理，但PI考虑到了胶体颗粒在许多化学和制药产品、化学加工以及各种微/纳米设备和系统的先进功能材料中的广泛应用。具体地说，这一建议力求更深入地理解限制诱导的玻璃化转变以及胶体薄膜动态响应的薄膜厚度依赖关系。研究小组将通过检查临界屈服应力及其结垢行为来阐明卡住的玻璃悬浮液的机械稳定性。该团队将进一步探索如何通过合理的剪切和表面纹理作用来使堵塞的胶体结构流态化。本研究的直接目标是：1)通过直接显微镜观察，表征当两个固体表面之间的间隙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)确定胶体薄膜在静止状态和外加剪切激励下的动力学性质，即迁移率、松弛过程和松弛时间，并将它们与块体悬浮液的流变性联系起来；3)研究更复杂的变量，如压缩速率、表面和地形组成对界面胶体层相态和粘弹性性质的影响。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)微球悬浮在密度和折射率匹配的非极性介质中，并限制在两个固体表面之间：1)光滑的未染色PMMA薄层，2)具有可控形貌和化学斑块的图案化模板。智力上的功绩。对受限胶体薄膜的玻璃化转变和界面性质，以及表面性质、压缩速率和剪切对胶体颗粒在复杂介质中的慢动态的作用的基本理解是巨大的挑战。除了材料特性之外，为了解决基本的胶体物理问题，微米间隙流变仪与激光扫描共聚焦显微镜集成在一起，可以同时控制表面分离，查看埋藏的胶体颗粒及其运动的三维结构，并测量粘弹性对外部力场的响应。这种新颖的实验装置是PI实验室独有的。它将提供一种新的方法来揭示胶体悬浮液、分子流体和许多其他复杂流体的限制诱导玻璃化转变的缓慢(1秒)和长期机制，这是流变学和布朗动力学模拟研究所不具备的。这项工作的技术意义集中在对玻璃化转变物理的一种新方法和理解上。所获得的知识将被用于合理的材料设计，以根据需要控制相结构、颗粒间相互作用和摩擦。这反过来可能会对坚韧结构陶瓷、润滑层和先进功能材料的合成、材料加工中的流态化以及其他技术领域产生广泛的影响，通过控制涂装、润滑等胶体系统的粘弹性。所获得的技术和知识将通过合理的推广应用到更广泛的领域，如高效的血细胞过滤和在多孔介质中流体传输过程中的节能。一个基础广泛的教育/外展计划被整合到这个跨学科研究计划中。在工程学妇女协会(SWE)的地方分会中，PI已经很活跃，它致力于招募和留住在许多工程学科中任职人数仍然不足的女学生。该协会还积极参与与巴黎圣母院的姊妹学院--圣玛丽学院--的共同交流项目，该学院是一所领先的私立女子天主教大学，教育女学生。这项建议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，该计划寻求与埃克森美孚和福特等石油和汽车行业建立强大的联盟，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.