The Rheology of Complex Suspensions In Viscoelastic Suspending Fluids

悬浮在液体中的颗粒在人类生活的各个方面都无处不在，包括在工业加工和制造以及人体本身中发挥关键作用。这些颗粒悬浮在其中的许多流体是弹性的-这意味着流体具有与流动相关的时间尺度相比并不短的时间记忆。例如，细胞上的尾巴状毛发，即纤毛，排列在人体气道中，在粘液中跳动，将其从肺部清除。粘液是一种弹性流体，粘液的弹性直接影响纤毛将粘液移出气道的能力。在另一种情况下，许多常见的复合塑料部件是以液态模制的，因此是流动的弹性流体并含有刚性颗粒添加剂。此外，石油工业使用的钻井泥浆和压裂液通常是含有支撑剂或钻井“刨花”的瓜尔胶溶液，并且再次涉及弹性流体中的悬浮液。虽然小分子或“牛顿”流体（如水或大多数油）中的悬浮液科学具有悠久的发展历史，但粘弹性流体中的颗粒悬浮液科学仍处于起步阶段。在对这些弹性流体的功能没有基本了解的情况下，对于给定的应用，经常在试错的基础上创建悬浮液。因此，该项目的目标是开发计算工具，使与粘弹性流体中粒子的集体效应相关的复杂物理模拟成为可能。这些工具将使人们能够直接设计悬浮液的流体特性，并对粘弹性流体在工业应用中的经济和安全使用具有巨大的影响。该研究将通过每年聘请一名K-12教师参与暑期实践研究计划来整合到高中课程中。该项目的总体目标是研究一系列日益复杂的颗粒悬浮液在粘弹性流体中的流变学，这些流体对能源行业，先进制造业和医疗/生物流体应用具有直接重要性。流变学，或宏观应力-应变关系，是理解这些材料功能的关键特征，因为它控制着它们在外力或内力下的宏观流动。采用大规模并行计算，该项目的第一个目标是检查与成型应用以及石油应用中的钻井泥浆或支撑剂相关的粘弹性剪切和拉伸流动中的球形颗粒。流变学将在增加的颗粒负载下测量，然后在适当的流动中模拟-宏观关系由微观图片的正确整体平均确定。这种颗粒运动与弹性流体的三维耦合以及由此产生的应力场（颗粒诱导流体应力）对于流体的工程应用至关重要。 该项目的第二个目标是使用相同的方法来研究可定向颗粒（不同长宽比的刚性球体）和可变形颗粒。对于后者，已经开发了一种新的计算工具，使用非结构化网格的弹性流体中的柔性颗粒固体的浸没有限元解。第三个目标是研究“活性物质”悬浮液，包括起伏和变形虫悬浮液，如蠕虫，精子和细菌游泳。后一个目标将首次阐明悬浮流体的弹性如何影响具有现实颗粒级分辨率的游泳的“主动悬浮液”的集体运动。因此，对这些应用的物理原理，甚至是这些进化的弹性流体悬浮液的生物学的基本理解的目标将得以实现。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Particles suspended in fluids are omnipresent in all aspects of human life, including playing key roles in industrial processing and manufacturing as well as within the body itself. Many of the fluids in which these particles are suspended are elastic - meaning the fluids have a memory in time that is not short compared to the time scales associated with the flow. For example, the tail-like hairs on cells, known as cilia, that line human airways beat in mucus to sweep it from the lungs. Mucus is an elastic fluid, and the elasticity of the mucus directly affects the ability of cilia to move mucus out of the airway. In another context, many common composite plastic parts are molded in the liquid state and, thus, are elastic fluids that flow and contain rigid particle additives. Further, drilling muds and fracking fluids, used by the oil industry, are typically guar gum solutions containing proppants or drilled "shavings" and, again, involve suspensions in elastic fluids. While the science of suspensions in small molecule or "Newtonian" fluids (like water or most oils) has a long, well-developed history, the science of particle suspensions in viscoelastic fluids is in its infancy. Without fundamental understanding of the function of these elastic fluids, suspensions are frequently created on a trial-and-error basis for a given application. Accordingly, the goal of the project is to develop computational tools that enable the simulation of the complex physics associated with the collective effects of particles in viscoelastic fluids. These tools will enable one to engineer the fluid properties of a suspension directly and has vast implications for the economical and safe use of viscoelastic fluids in industrial applications. The research will be integrated into high school curriculum by engaging a K-12 teacher each year in a hands-on summer research program.The overall goal of the project is to examine the rheology of a series of increasingly complex particulate suspensions in viscoelastic fluids that are of direct importance to the energy industry, advanced manufacturing, and medical/biofluids applications. The rheology, or macroscopic stress-strain relationship, is the key feature in understanding the function of these materials since it governs their macroscopic flow under applied or internal forces. Employing large-scale, parallel computing, the first objective of the project is to examine spherical particles in viscoelastic shear and extensional flows associated with molding applications as well as drilling muds or proppants in oil applications. The rheology will be measured at increased particle loading and then simulated in the appropriate flow - with the macroscopic relationships determined from the correct ensemble-averaging of the microscopic picture. This 3-D coupling of the particle motions to the elastic fluid and resulting stress field (particle-induced fluid stress) is critical to the engineering application of the fluids. The second objective of the project is to use the same approach to study orientable particles (rigid spheroids of varying aspect ratio) and deformable particles. For the latter, a new computational tool using an Immersed Finite Element solution of flexible particulate solids in elastic fluids with unstructured grids has been developed. The third objective examines "active matter" suspensions, including undulating and amoeboid suspensions such as nematode worms, sperm, and bacterial swimming. The latter objective will, for the first time, shed light on how elasticity in the suspending fluid affects the collective motion of "active suspensions" with realistic particle-level resolution of the swimming. Thus, the goal of foundational understanding of the physical principles governing these applications, and even the biology of these evolved elastic fluid suspensions, will be achieved.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.