Collaborative Research: Experimental and Computational Studies of Flow and Clogging of Deformable Particles under Confinement

柔软、可变形的颗粒在科学和工程的许多领域都扮演着重要的角色，从生物细胞到组成蛋黄酱、花生酱和牛奶等乳状液的水中的脂肪油滴。具有不同宽度的微小通道的微流控装置被用于处理可变形颗粒和流体的混合物，以及操纵DNA分子。然而，微流控设备经常在狭窄附近堵塞，这是昂贵的，因为发生这种情况时必须更换设备。人们对刚性颗粒的堵塞进行了广泛的研究，比如从筒仓中流出的颗粒，但对可变形颗粒的堵塞了解较少。特别是，尚不清楚颗粒的变形性和粘性或凝聚力如何影响堵塞。例如，可变形和粘合的粒子会改变形状并在收缩时相互流动，还是会形成拱形并堵塞系统？该项目将流经微流控装置的乳液滴的实验与对可变形颗粒的新型计算机模拟相结合，以了解它们是如何堵塞的。这项工作将有助于未来设计关键的微流控装置，这些装置涉及细胞-液体混合物的生物样品的工业处理、过滤和分析。从筒仓中颗粒状物质的流动到血液细胞在静脉中的流动，各种系统都可以观察到由流动引起的堵塞或堵塞。在硬的摩擦颗粒的情况下，堵塞得到了很好的研究，但当颗粒可变形和粘合时，人们对堵塞的了解很少。该项目采用了具有可调变形和粘附性的乳液滴在微流控装置中流动的悬浮实验，以及为模拟乳液滴而设计的明显可变形颗粒流动的新模拟。实验与计算相结合的方法能够较好地解决变形性、颗粒力学响应和粘附性对堵塞概率的影响。一个关键的焦点是堵塞过程中颗粒重排在疏通悬浮液中的作用。在颗粒材料的堵塞过程中，颗粒是静态的，堵塞具有很长的寿命。然而，如果颗粒是可变形的，堵塞悬浮液中的颗粒形状松弛和应力重新分布可能会导致间歇性的堵塞释放和雪崩。此外，该项目还将研究描述流量如何随收缩宽度变化的贝弗洛定律在可变形颗粒和粘性颗粒的情况下如何变化。计算和实验研究的结合将有助于开发一个全面的理论框架，以预测在给定颗粒特性、流速和收缩宽度的情况下何时会形成堵塞。随着微流控设备越来越多地用于分析胶体颗粒和细胞的悬浮液，设计下一代高效高通量微流控设备需要基于单粒子特性(如变形性、弹性和粘附性)的预测框架。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Squishy, deformable particles play an important role in many fields of science and engineering, from the biological cells to droplets of fatty oils in water that make up emulsions like mayonnaise, peanut butter, and milk. Microfluidic devices with tiny channels of varying widths are used to process mixtures of deformable particles and fluids and to manipulate DNA molecules. However, microfluidic devices frequently clog near constrictions, which is expensive since the device must be replaced when this occurs. Clogging has been studied extensively for rigid particles, like grains flowing out of a silo, but clogging of deformable particles is less well understood. In particular, it is unclear how particle deformability and stickiness or cohesion affects clogging. For example, will deformable and cohesive particles change shape and flow past each other at constrictions, or will they form arches and clog the system? This project combines experiments of emulsion droplets flowed through microfluidic devices with novel computer simulations of deformable particles to understand how they clog. This work will aid in future designs of critical microfluidic devices involved in industrial processing, filtration, and analysis of biological samples of cell-fluid mixtures. Flow-induced jamming, or clogging, is observed across a wide range of systems, from flows of granular materials in silos to flows of blood cells through veins. Clogging is well studied in the case of hard, frictional grains, but is poorly understood when particles are deformable and cohesive. This project employs experiments of suspensions of emulsion droplets with tunable deformability and adhesion flowed through microfluidic devices, along with novel simulations of flows of explicitly deformable particles designed to model emulsion droplets. The combined experimental-computational approach can disentangle the effects of deformability, particle mechanical response, and adhesion on clogging probability. One key focus is the role of particle rearrangements during clogs in unjamming the suspensions. During clogs of granular materials, particles are static and clogs have long lifetimes. However, if particles are deformable, particle shape relaxation and stress redistribution in a clogged suspension can lead to intermittent clog release and avalanching. Additionally, this project will investigate how the Beverloo Law, which describes how flow rate changes with constriction width, changes in the case of deformable and adhesive particles. The combination of computational and experimental studies will aid the development of a comprehensive theoretical framework to predict when a clog will form given the particle properties, flow rate, and constriction width. With the increased use of microfluidic devices to analyze suspensions of colloidal particles and cells, a predictive framework for clogging based on single-particle properties like deformability, elasticity and adhesion is required to design the next generation of efficient high-throughput microfluidic devices.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.