Structural Heterogeneity, Microhydrodynamics and the Non-Linear Viscoelasticity of Colloidal Gels

胶体凝胶的结构异质性、微流体动力学和非线性粘弹性

• 批准号: 0522340
• 负责人: Michael Solomon
• 金额: --
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-01 至 2008-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0522340&HistoricalAwards=false
• 关键词: Structural; Heterogeneity; Microhydrodynamics; Non; Linear

ABSTRACT - 0522340University of MichiganGels of colloidal particles are systems with slow, constrained dynamics and unusual, viscoelastic rheology. They are central to the chemical processing of ceramics, the formation of membranes for microfiltration and the quality of paints, finishes and coatings. Next generation technologies such as direct-write assembly and microfluidic valving also rely on the gelation transition and the rheological properties of colloidal particle gels. Thus, fundamental understanding that could be applied to predict the gelation transition, to control the microscopic structure and dynamics of gels as well as to exploit their unusual non-linear rheology would broadly impact technology development in these areas. Scientifically, there is a need for experiments that can discriminate between theories of the gelation transition that are based on the mode-coupling framework and on the dynamic equilibrium clustering approach. In addition, the relationship between structural heterogeneity and gel microhydrodynamics should be discovered to understand the role of dynamic heterogeneity in gels. Finally, even qualitative features of local structural evolution upon the application of non-linear deformation have yet to be resolved through experiment. To address the scientific questions that underlie these technological needs, we will execute an experimental research program to observe local correlations among structure, dynamics and non-linear viscoelasticity of colloidal gels.The intellectual merit of our research plan arises from our comprehensive application of confocal optical microscopy in pursuit of these aims. The power of confocal microscopy rests on its ability to directly visualize local, colloid-level structure and dynamics in three dimensions (3D) and with nanoscale resolution. We will principally study suspensions of micron-scale stericallystabilized colloidal poly(methyl methacrylate) in refractive-index and density-matched solvents. Short-range attractive interactions leading to gelation will be induced by non-adsorbing polymer. The control parameter governing the strength of the short-range attraction will be the concentration of polymer. Confocal microscopy of 3D image volumes will be used to quantify the size and heterogeneity of clusters and strings induced by gelation. The local structure will be characterized by measurement of the distribution of contact numbers of particles in the gel. These structural measures will be used to test specific predictions of mode coupling and thermodynamic theories of gelation. To study dynamical heterogeneity and other microhydrodynamical features of gels, structure will be correlated with single and collective particle dynamics quantified by 3D particle tracking. Finally, transient structural evolution will be monitored in start-up of steady-shear flow and after step-strain experiments through in situ confocal microcopy. Novel aspects of the flow experiments will be their attention to non-linear phenomena, their control of wall slip through surface topology engineering, and their execution with materials that will yield a never before available picture of the local, rotational dynamics of colloids in the gel. These direct visualization experiments are distinct from previous light, neutron and X-ray scattering studies because they specifically probe local phenomena and distributions of structure and dynamics that cannot commonly be obtained from the ensemble-averaged results of scattering. This study will broadly impact technology and engineering in areas as diverse as ceramic, membranes and direct write assembly by its elucidation of new scientific understanding of the relationship among the gelation transition, microscopic gel structure and dynamics as well as macroscopic flow. Additional outcomes with broader impact include the training of one graduate student in state-of-the-art methods in confocal microscopy, colloidal science and rheology as well as new development of a summer outreach program that introduces middle school girls to science and engineering through focused, hands on lab activities and experiments in complex fluids, chemical engineering and materials science.

摘要-0522340胶体颗粒的密歇根州的University是具有缓慢，约束动力学和异常的粘弹性流变学的系统。它们是陶瓷化学加工的核心，形成用于微滤的膜以及油漆，饰面和涂料的质量。下一代技术，例如直接 - 丝集和微流体瓣膜，也依赖于胶体颗粒凝胶的凝胶化过渡和流变特性。因此，可以应用于预测凝胶化过渡的基本理解，以控制凝胶的微观结构和动力学以及利用其异常的非线性流变学将广泛影响这些领域的技术发展。从科学上讲，有必要进行实验，可以区分基于模式耦合框架和动态平衡聚类方法的凝胶化过渡理论。此外，应发现结构异质性与凝胶微水力动力学之间的关系，以了解动态异质性在凝胶中的作用。最后，即使在应用非线性变形时，局部结构演变的定性特征也尚未通过实验解决。为了解决这些技术需求的基础的科学问题，我们将执行一项实验研究计划，以观察胶体凝胶的结构，动力学和非线性粘弹性之间的局部相关性。我们的研究计划的知识分子优点源于我们在追求这些目标方面的共同光学显微镜的全面应用。共聚焦显微镜的力量取决于其在三个维度（3D）中直接可视化局部，胶体级结构和动力学的能力，并具有纳米级分辨率。我们将主要研究在折射率和密度匹配的溶剂中的微米尺度定量稳定的胶体聚（甲基丙烯酸甲酯）的悬浮液。不吸附的聚合物将引起导致凝胶化的短距离相互作用。控制短距离吸引力强度的控制参数将是聚合物的浓度。 3D图像体积的共聚焦显微镜将用于量化凝胶化引起的簇和字符串的大小和异质性。局部结构的特征是测量凝胶中颗粒的接触数分布。这些结构测量将用于测试模式耦合和热力学理论的特定预测。为了研究凝胶的动态异质性和其他微水动力学特征，结构将与通过3D粒子跟踪量化的单个和集体粒子动力学相关。最后，将在稳定剪切流动的启动以及通过原位共聚焦微拷贝进行瞬时结构演化。流动实验的新颖方面将是他们对非线性现象的关注，对壁滑动通过表面拓扑工程的控制以及用材料执行，这些材料将产生凝胶中胶体的局部旋转动力学的可用图片。这些直接可视化实验与以前的光，中子和X射线散射研究不同，因为它们专门探测了局部现象以及结构和动力学的分布，这些现象通常是从散射的集合平均结果中获得的。这项研究将通过阐明胶质过渡，微观凝胶结构和动力学以及宏观流动之间的新科学理解，从而广泛影响陶瓷，膜和直接写入等多样性的技术和工程。具有更广泛影响的其他结果包括培训一名研究生在共聚焦显微镜，胶体科学和流变学领域的最先进方法中，以及夏季外展计划的新发展，该计划通过专注于科学和工程，通过专注于科学和工程，进行实验室活动和实验室活动，并在复杂的液体，化学工程，化学工程和材料科学领域进行实验室活动和实验。