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

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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.