Flow, Memory and Aging of Soft Particle Pastes

软颗粒浆料的流动、记忆和老化

• 批准号: 0854420
• 负责人: Roger Bonnecaze
• 金额: $ 28万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0854420&HistoricalAwards=false
• 关键词: Flow; Memory; Aging; Soft; Particle

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0854420BonnecazeIntellectual Merit: Many concentrated materials consist of soft particles (e.g., emulsions, elastic particles, microgels, star polymers or polymer-coated particles) packed and deformed into an amorphous state. These pastes are important as rheological modifiers for food, materials and coating processes, friction reduction in cement pumping and hydrofracturing. There are, however, several aspects of their behavior that are not fully understood. Soft particle pastes (SPPs) display complex shear thinning, normal and yield stresses, coating instabilities, slip, memory and aging. Their aging behavior is similar to that in structural, spin and polymer glasses. We propose to develop simulations and models to describe the behavior of these soft-particle pastes in order to: 1) develop a complete rheological model for soft particle pastes with arbitrary interparticle potentials to describe their elasto-plastic flow; 2) identify the microstructural events that occur during flow and that give rise to aging and memory in soft particle pastes in order to accelerate, stop or otherwise mitigate these effects; 3) test existing theories of aging and develop a new theory for aging and memory of these materials specifically accounting for the elastohydrodynamic interactions. To achieve these goals we will build on our discovery of the importance of elastohydrodynamic interactions for these materials and our recent simulations and experiments on the viscoelastic properties of microgel suspensions undergoing shear. Specifically, we will: 1) develop a theory to describe the microstructure in terms of the pairwise, particle distribution function of the relaxed, unstrained paste for arbitrary interparticle forces and predict elastic properties of SPPs; 2) develop a theory that determines the perturbed distribution function under flow and thus predict the yield strength and the general viscoelastic properties of SPPs; 3) modify our existing 3D particle-based dynamic simulation of soft particle pastes to simulate aging and memory; 4) use the simulations for parametric studies of aging and memory of soft particle pastes correlating macroscopic behavior and microstructural rearrangements; 5) evaluate existing models and develop new models for the bulk rheology, aging and memory of soft particle pastes. For all stages of this work, we will continually compare our theoretical predictions to experiments in the literature and those conducted by a collaborator at the ESPCI. The simulations will allow the direct connection between the macroscopic properties (e.g., yield stress, modulus, effective viscosity, normal stresses, aging and memory) to the microscopic interactions of the soft particles and a fundamental understanding of the origins of their rheology. Broader Impacts: The rheology of SPPs appears to be universal across a broad array of deformable particles ranging in size from nanometers to hundreds of microns. The knowledge gained from this work will provide engineers and colloid scientists a means to tailor the formulation of soft particle pastes to have desired rheological properties. Theories from this proposed work for predicting the non-equilibrium microstructure will also provide a new methodology for modeling the properties of highly concentrated, amorphous suspensions of soft particles and other complex fluids. The aging and memory phenomena seen in pastes are also seen in many other systems, including nematic polymers and spin and structural glasses. The proposed work will provide fundamental insights into these behaviors. The aging phenomenon in pastes is part of a broader issue of and an industrially important concern about shelf life of formulations of suspensions. The results of this work will provide guidance into controlling aging and shelf-life. This proposed will involve the education of one graduate student and two undergraduate students over the course of the project. They will become skilled in rheology of complex fluids, computational simulation and modeling.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。乳液、弹性颗粒、微凝胶、星星聚合物或聚合物涂覆的颗粒）填充并变形为无定形状态。这些糊剂作为食品、材料和涂层工艺的流变改性剂、水泥泵送和水力压裂中的减摩剂是重要的。然而，它们的行为有几个方面还没有完全了解。软颗粒浆料（SPP）具有复杂的剪切变稀、法向应力和屈服应力、涂层不稳定性、滑移、记忆和老化等特性。它们的老化行为与结构玻璃、自旋玻璃和聚合物玻璃中的老化行为相似。我们建议开发模拟和模型来描述这些软颗粒浆料的行为，以便：1）开发具有任意颗粒间势的软颗粒浆料的完整流变模型来描述其弹塑性流动; 2）识别流动期间发生的微观结构事件，并引起软颗粒浆料中的老化和记忆，以加速、停止或以其他方式减轻这些效应; 3）测试现有的老化理论，并发展一种新的理论，用于这些材料的老化和记忆，特别是考虑弹性流体动力学相互作用。 为了实现这些目标，我们将建立在我们发现的这些材料的弹性流体动力学相互作用的重要性和我们最近的模拟和实验的粘弹性微凝胶悬浮液进行剪切。具体而言，我们将：1）发展一种理论来描述微观结构，该理论根据松弛的、无应变的糊状物对于任意颗粒间力的成对颗粒分布函数，并预测SPP的弹性性质; 2）发展一种理论，该理论确定流动下的扰动分布函数，从而预测SPP的屈服强度和一般粘弹性性质; 3）修改我们现有的软颗粒浆料的基于3D颗粒的动态模拟以模拟老化和记忆; 4）使用模拟用于与宏观行为和微观结构重排相关的软颗粒浆料的老化和记忆的参数研究; 5）评估现有模型并开发新的模型用于软颗粒浆体的体积流变学、老化和记忆。在这项工作的所有阶段，我们将不断将我们的理论预测与文献中的实验以及ESPCI合作者进行的实验进行比较。模拟将允许宏观性质（例如，屈服应力、模量、有效粘度、法向应力、老化和记忆）到软颗粒的微观相互作用，以及对其流变学起源的基本理解。更广泛的影响：SPP的流变学似乎是通用的，跨越尺寸从纳米到数百微米的可变形颗粒的广泛阵列。从这项工作中获得的知识将为工程师和胶体科学家提供一种方法来定制软颗粒糊剂的配方，以具有所需的流变性能。从这个建议的工作预测的非平衡微观结构的理论也将提供一个新的方法来建模的软颗粒和其他复杂的流体的高度集中，无定形悬浮液的属性。在浆料中看到的老化和记忆现象也出现在许多其他系统中，包括聚合物和自旋和结构玻璃。拟议的工作将为这些行为提供基本的见解。糊剂中的老化现象是关于悬浮液制剂的保质期的更广泛问题和工业上重要关注的一部分。这项工作的结果将为控制老化和保质期提供指导。这将涉及一个研究生和两个本科生在项目过程中的教育。他们将熟练掌握复杂流体的流变学，计算机模拟和建模。