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年的《美国回收与再投资法》（公法111-5）进行资助的。0854420BonNecazeintellectualfelutal优点：许多集中材料由软颗粒（例如，乳液，弹性颗粒，微凝胶，恒星，星形聚合物或聚合物聚合物或聚合物涂层的颗粒）组成，并被包装成一个变形的状态。这些糊状物作为食物，材料和涂料过程的流变修饰符，水泥泵送和氢反应的摩擦减少。但是，他们行为的几个方面尚未完全理解。软颗粒糊（SPP）显示复杂的剪切稀疏，正常和屈服应力，涂料不稳定性，滑动，记忆和老化。它们的衰老行为与结构，自旋和聚合物玻璃杯中的行为相似。我们建议开发模拟和模型来描述这些软粒子糊的行为，以：1）为具有任意颗粒质电位的软颗粒糊的完整的流变模型，以描述其弹性流动； 2）确定流动过程中发生的微观结构事件，并引起软颗粒糊中的衰老和记忆，以加速，停止或以其他方式减轻这些影响； 3）测试现有的衰老理论，并开发出一种新理论，用于对这些材料的老化和记忆，这些理论专门考虑了弹性水动力相互作用。 为了实现这些目标，我们将基于发现这些材料的弹性水动力相互作用的重要性，以及我们最近对Microgel悬浮液的粘弹性特性的模拟和实验。具体而言，我们将：1）开发一种理论来描述微观结构，以对任意颗粒力的宽松，未训练的糊状物的颗粒分布函数以及预测SPP的弹性特性； 2）开发一种理论，该理论决定流动下的扰动分布函数，从而预测属于SPP的屈服强度和一般粘弹性。 3）修改我们现有的基于3D粒子的动态模拟软颗粒糊，以模拟衰老和记忆； 4）使用模拟进行衰老和记忆的参数研究，使宏观行为和微结构重排相关； 5）评估现有模型并开发新的模型，用于散装流变学，老化和软质糊的记忆。对于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的实验以及ESPCI合作者进行的实验进行比较。这些模拟将允许宏观特性（例如，屈服应力，模量，有效粘度，正常应力，衰老和记忆力）与软颗粒的微观相互作用以及对其流变学起源的基本了解。更广泛的影响：SPP的流变学似乎是从纳米到数百微米的一系列可变形颗粒中普遍存在的。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量身定制软颗粒糊的方法以具有所需的流变特性。这项提出的预测非平衡微观结构的拟议工作的理论还将提供一种新的方法，用于建模高度浓缩的软颗粒和其他复杂流体的高度浓缩，无定形悬浮液的性质。在糊状物中也看到了糊状物中的衰老和记忆现象，包括列明聚合物以及自旋和结构玻璃。拟议的工作将为这些行为提供基本的见解。糊状物中的衰老现象是对悬浮液配方的保质期的更广泛问题的一部分，也是工业上重要的关注。这项工作的结果将为控制衰老和保质期提供指导。这项建议将涉及一名研究生和两名本科生的教育。他们将熟练地精通复杂流体，计算模拟和建模的流变学。