Stress Formation and Relaxation in colloidal Dispersions: Transient, Nonlinear Microrheology

胶体分散体中应力的形成和松弛：瞬态、非线性微流变学

• 批准号: 1605836
• 负责人: Roseanna Zia
• 金额: $ 28.24万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2017-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1605836&HistoricalAwards=false
• 关键词: Stress; Formation; Relaxation; colloidal; Dispersions

PI: Zia, RoseannaProposal Number: 1605836The goal of the proposed research is to investigate colloidal dispersions when forces and stresses acting on them change. Both theoretical analysis and a class of computations known as Accelerated Stokesian Dynamics simulations will be used to accomplish this goal. The work could have an impact on the chemical and food industry, where control of material properties and of complex fluids, like colloids, is important.The goal of the proposed research is to develop predictive theory and computational models for the temporal formation and relaxation of viscosity and stress in colloidal dispersions via the framework of active microrheology, with a focus on connections to particle microstructure as it evolves in time. Most non-equilibrium microrheological work to date has focused on steady-state flow behavior, yielding insight into steady-state non-Newtonian behaviors, relating them to flow-strength induced changes in the relative contributions of hydrodynamic, Brownian, and interparticle forces. However, understanding of how such relative contributions evolve in time-during flow startup and cessation-lags behind. Such understanding is key to resolving important questions such as the origins of stress "overshoots" during flow startup, and whether structural evolution and rheological evolution reach steady state simultaneously. The results of the proposed research are of fundamental scientific interest and will impact applications as diverse as intracellular flow, drilling fluids, and impact-resistant materials. The PI hypothesizes that the relative contributions of hydrodynamic, interparticle, and Brownian forces to the stress and viscosity in colloidal dispersions are not instantaneously formed upon flow startup, and thus that the climb to steady state rheology may lead or lag formation of steady state structure. The proposed work will combine theoretical and computational rheological studies. Theoretical studies will center on formulation and solution of time-dependent Smoluchowski equations, which will then be utilized to compute suspension viscosity and stress as it evolves in time, for any range of interparticle repulsion (i.e., strength of hydrodynamic interactions), particle size ratio, and attractive potentials. The educational plan will improve the participation of underrepresented students via mentored learning utilizing guided, hands-on experiments. The PI will develop fluid mechanics modules for classrooms and outreach at Cornell University, rheology conferences, and quarterly "Science Days" at National Academy Foundation high schools for underrepresented minority students.

主要研究者：Zia，Roseanna提案编号：1605836拟议研究的目标是研究当作用于它们的力和应力发生变化时的胶体分散体。理论分析和一类被称为加速斯托克斯动力学模拟的计算将用于实现这一目标。这项工作可能会对化学和食品工业产生影响，在这些行业中，控制材料特性和复杂流体（如胶体）非常重要。拟议研究的目标是通过活性微流变学框架，为胶体分散体中粘度和应力的时间形成和松弛开发预测理论和计算模型，重点关注随着时间的推移与颗粒微观结构的联系。迄今为止，大多数非平衡微观流变学工作都集中在稳态流动行为上，深入了解稳态非牛顿行为，将它们与流体动力学、布朗运动和颗粒间力的相对贡献中的流动强度引起的变化相关联。然而，对这种相对贡献如何随时间演变（在流启动和停止期间）的理解却落后了。这样的理解是解决重要问题的关键，如应力的起源“过冲”在流动启动，以及结构演化和流变演化是否同时达到稳态。拟议研究的结果具有根本的科学意义，并将影响细胞内流动，钻井液和抗冲击材料等各种应用。PI假设流体动力学、颗粒间力和布朗力对胶体分散体中的应力和粘度的相对贡献在流动启动时不是瞬时形成的，因此向稳态流变学的爬升可能导致或滞后于稳态结构的形成。拟议的工作将结合联合收割机理论和计算流变学研究。理论研究将集中在时间依赖性Smoluchowski方程的公式化和求解上，然后将利用该方程来计算悬浮液粘度和应力，因为它随时间演变，对于任何范围的颗粒间排斥（即，流体动力学相互作用的强度）、粒度比和吸引势。该教育计划将通过利用指导性实践实验的指导学习，提高代表性不足的学生的参与程度。PI将为康奈尔大学的教室和外展开发流体力学模块，流变学会议，并在国家科学院基金会高中为代表性不足的少数民族学生开发季度“科学日”。