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

黏糊糊的、可变形的颗粒在许多科学和工程领域中发挥着重要作用，从生物细胞到水中的脂肪油滴，这些脂肪油滴构成了蛋黄酱、花生酱和牛奶等乳液。具有不同宽度的微小通道的微流体装置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，微流体装置经常在收缩部附近堵塞，这是昂贵的，因为当这种情况发生时必须更换装置。对于刚性颗粒（如从筒仓中流出的谷物）的堵塞已经进行了广泛的研究，但是对于可变形颗粒的堵塞还不太清楚。特别是，目前还不清楚颗粒的变形性和粘性或凝聚力如何影响堵塞。例如，可变形和粘性颗粒会改变形状并在收缩处彼此流过，还是会形成拱形并堵塞系统？该项目将乳液液滴流过微流体装置的实验与可变形颗粒的新型计算机模拟相结合，以了解它们如何堵塞。这项工作将有助于未来设计的关键微流控设备参与工业处理，过滤和分析的细胞流体混合物的生物样品。从筒仓中的颗粒材料流动到通过静脉的血细胞流动，在广泛的系统中观察到流动诱导的堵塞或堵塞。在硬的摩擦颗粒的情况下，堵塞被很好地研究，但是当颗粒是可变形的和内聚的时，却知之甚少。该项目采用了可调变形性和粘附性的乳液液滴悬浮液流过微流体装置的实验，沿着与明确可变形颗粒的流动的新模拟设计用于模拟乳液液滴。实验-计算相结合的方法可以理清变形性、颗粒机械响应和粘附对堵塞概率的影响。一个关键的焦点是在解除堵塞的悬浮液中的堵塞期间颗粒重排的作用。在颗粒材料堵塞期间，颗粒是静态的，并且堵塞物具有长的寿命。然而，如果颗粒是可变形的，则堵塞悬浮液中的颗粒形状松弛和应力重新分布可导致间歇性堵塞释放和雪崩。此外，本项目将研究如何贝弗卢定律，它描述了如何流速与收缩宽度的变化，在可变形和粘性颗粒的情况下变化。计算和实验研究的结合将有助于发展一个全面的理论框架，以预测何时会形成堵塞给定的颗粒特性，流速和收缩宽度。随着微流控设备在分析胶体颗粒和细胞悬浮液方面的应用越来越多，基于单颗粒特性（如变形性）的堵塞预测框架，弹性和附着力是设计下一代高效高该奖项反映了NSF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进行评估，被认为值得支持审查标准。

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.