Advanced rheological studies of glass-forming colloidal dispersions: Combining experiment and theory

胶体分散体提供了广泛的技术应用，从化妆品到食品科学到建筑材料。了解它们在外加强磁场下的力学行为对于发展基础理论以及最终产品的加工和应用条件至关重要。虽然胶体溶液在均匀剪切流中的流动特性在基于粒子的理论中得到了很好的理解，但到目前为止，对非均匀、边界驱动、非剪切或混合流的研究仍然主要是唯象的。特别重要的是高浓度，其中粘弹性效应显着改变的分散properties.Recently，微观模式耦合理论（MCT）的结构动力学在液体中已被扩展到均匀流的本构形式，使其能够预测的流量控制的非线性流变散装浓悬浮液。在这个项目中，我们的目标是推广MCT强非简单流，包括应力控制和非均匀的。我们将结合联合收割机的推广MCT与先进的流变学研究模型胶体悬浮液（由热敏PNiPAM微凝胶），以获得一组一致的测量。为了实现这一目标，先进流变特性的开发或改进将是该项目的一部分，例如，预期增加确定剪切下产生的法向力的灵敏度。具体而言，我们的合作项目将研究以下课题：1. 拉伸流和测量的正常应力将使我们能够测试张量性质的应力应变关系的MCT超越简单的剪切流。 2. 大振幅振荡剪切，傅立叶变换流变学和高次谐波的测量将在应变和应力控制下进行研究，以了解迟滞和亚稳态的滞后。变形模式的叠加将为流动驱动的流化、历史相关的机械性能或残余应力提供额外的见解。 毛细管流动中的约束将提供对流动下的空间相关性、不均匀性和不稳定性（如剪切带）的深入了解。再次，准备历史的依赖性将被详细研究。在整个过程中，一个统一的理论方法将开发和胶体模型系统的实验验证。因此，一个一致的基本描述将出现，这可以作为一个合理的设计浓缩复杂的分散体的加工技术的基础。

Colloidal dispersions offer a wide range of technological applications ranging from cosmetics over food science to building materials. Understanding their mechanical behaviour under applied strong fields is crucial for developing a fundamental theory as well as for processing and the application conditions of the final products. While the flow properties of colloid solutions in homogeneous shear flows are rather well understood in particle based theories, approaches to inhomogeneous, boundary-driven, non-shear or mixed flows remain largely phenomenological up to now. Especially important are high concentrations, where viscoelastic effects dramatically change the dispersion properties.Recently, the microscopic mode coupling theory (MCT) of the structural dynamics in liquids has been extended to a constitutive form for homogeneous flows, enabling it to predict the flow-controlled nonlinear rheology of bulk concentrated suspensions. In this project, we aim to generalize MCT to strong non-simple flows including stress-controlled and inhomogeneous ones. We will combine the generalization of MCT with advanced rheological studies on model colloidal suspensions (consisting of thermosensitive PNiPAM microgels) to obtain a consistent set of measurements. To achieve this goal, the development or improvement of advanced rheological characterizations will be part of the project, e.g. an intended increase in the sensitivity for the determination of resulting normal forces under shear. In detail, the following topics will be studied in our cooperation project:1. Extensional flows and measurements of normal stresses will enable us to test the tensorial nature of stress-strain relations from MCT beyond simple shear flows. 2. Large amplitude oscillatory shearing, Fourier transform rheology and measurements of the higher harmonics will be investigated under strain and stress control in order to understand hysteresis in sluggish and metastable states. Superposition of deformation modes will provide additional insights into flow-driven fluidization, history dependent mechanical properties or residual stresses.3. Confinement in capillary flows will provide insights into spatial correlations, heterogeneities and instabilities (like shear-banding) under flow. Again, the dependence on preparation history will be studied in detail. Throughout, a unified theoretical approach will be developed and verified by experiment on the colloidal model system. Thus a consistent fundamental description will emerge, which can serve as basis for a rational design of processing technologies of concentrated complex dispersions.