Collective physics of slowly sedimenting anisotropic objects

固体颗粒在液体中的沉降与许多技术、生物和地球物理过程有着广泛的关系。固体颗粒从液相中沉降是化学萃取、提纯和分离、矿石清洗以及食品和饮料加工中普遍存在的过程。在自然界中，沉淀在湖泊、河流和海洋中是重要的地球物理过程，就像岩浆中的结晶相下沉和云中的冰晶沉降一样。海洋中碳捕获的一个关键阶段是死亡浮游植物的下沉。大多数相关的系统由非球形组成（棒、板、片或分枝丝状结构），然而，实验室实验和理论在很大程度上解决了球形的情况。在这个项目中，执行了一系列的实验，通过各种实验技术来研究非球形形状的沉降。除了两名研究生外，还有多名本科生也接受了相关方法的培训。PI通过在马萨诸塞大学阿默斯特分校组织名为“软固体和复杂流体”的年度暑期学校，以及为本科生开设新的暑期学校，为其所在机构以外的软物质物理学研究生教育做出了贡献。在活动期间，PI与一位同事和两位高中教师为初中和高中教师举办了一个名为“我们周围的模式”的年度暑期项目。技术摘要：对球体沉降悬浮液的研究已经表明，这是一个棘手的多体问题，然而，各向异性物体在悬浮液中的集体沉降的实际相关情况却很少受到重视。最近的研究表明，通过粒子形状增加方向自由度会导致新的定性现象，并使答案与更大范围的物理相关系统更相关。在本研究过程中，实验将以一系列粒子形状进行，以逐步建立较低对称性物体的词汇表，从轴对称非极性形状（圆盘，棒状，椭球体）开始，轴对称极性形状，双轴形状，手性形状，最后是无明显对称性的不规则形状。本着从简单到更复杂系统的精神，实验从研究单粒子沉降开始，然后是对动力学，最后是控制体积分数的悬浮液中的沉降。悬架将在一些几何形状中进行研究，以了解约束和硬壁的影响。这些系统将通过视频成像、x射线CT和光散射等不同的探针来测量平均沉降率、空间梯度以及浓度、速度和方向场的波动。实验得到了图解数值计算的支持，使用stokeslet表示来捕捉粒子几何形状的对称性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstractThe settling of solid particles in a liquid is of wide relevance to a number of technological, biological, and geophysical processes. Sedimentation of solid particulates out of a liquid phase is a ubiquitous process in chemical extractions, purifications and separations, cleaning of ores, and processing of foods and beverages. In the natural world, settling in lakes, rivers and oceans are important geophysical processes, as are sinking of crystalline phases within magma and the settling of ice crystallites within clouds. A crucial phase in carbon capture in the oceans is the sinking of dead phytoplankton. Most relevant systems are comprised of nonspherical shapes (rods, plates, flakes, or branched filamentary structures) and yet, laboratory experiments and theory have largely addressed the case of spherical shapes. In this project, a series of experiments are executed to study the settling of non-spherical shapes by a variety of experimental techniques. In addition to two graduate students, a number of undergraduate students are also trained in the relevant methods. The PI contributes to graduate education in soft matter physics beyond their home institution by organizing an annual summer school at UMass Amherst entitled Soft Solids and Complex Fluids, and launching a new summer school for undergraduate students. During the activity, the PI with a colleague and two high-school teachers run an annual summer program for middle- and high-school teachers entitled Patterns Around Us.Technical abstractStudies of sedimenting suspensions of spheres have already shown this to be a formidable many-body problem, however, the practically relevant case of the collective sedimentation of anisotropic objects in suspension has received less attention. Recent studies show that adding an orientational degree of freedom via the particle shape leads to qualitatively new phenomena, and makes the answers more relevant to a far larger class of physically relevant systems. In the course of this research, experiments are to be conducted with a range of particle shapes to build up a vocabulary of progressively lower symmetry objects, starting with axially symmetric non-polar shapes (discs, rods, ellipsoids), axially symmetric polar shapes, biaxial shapes, chiral shapes, and finally, irregular shapes with no evident symmetry. In the spirit of progressing from simple to more complex systems, the experiments start by studying single-particle sedimentation, then pair dynamics, and finally sedimentation in suspensions of controlled volume fraction. Suspensions will be studied in a few geometries to understand the effect of confinement and hard walls. These systems will be interrogated by a few different probes such as video imaging, x-ray CT, and light scattering to measure mean settling rate, spatial gradients as well as fluctuations in concentration, velocity and orientation fields. The experiments are supported with schematic numerical calculations using stokeslet representations that capture the shape symmetry of particle geometry.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.