Complex Fluid Flows in Confinement: Squishing, Clogging, and Intermittent Dynamics


Monday, October 23, 2023 - 3:30pm to 4:30pm


ESB 1001


Professor Sara M. Hashmi

Intermittency and clogging of complex fluids flowing through small spaces can occur nearly anywhere: in the porous media of the earth, in industrial flows through hoppers, in water filters, 3D printing nozzles, and in some of the worst instances, in our blood vessels. These examples include flows of colloidal particles, granular media, and even crosslinking polymers. Despite the differences in the type of complex fluid involved, some aspects of clogging are universal, like its stochastic nature and the importance of the constituent material properties. At the same time, understanding the nature of clogging is key to controlling or preventing it, and facilitates improved design of filters, hoppers, and even diagnostic tools. This talk explores intermittency and clogging in pores from the centimeter scale to the micron scale, investigating granular hopper flows and microfluidic polymer flows. Despite salient differences between these two systems, we find the material properties of the complex fluid to govern flow behavior. On the macro-scale, a quasi-2D rotating hopper is used to investigate both jamming and avalanche flows in small-system mixtures of soft and rigid particles. Increasing the fraction of soft particles in the mixture can alleviate jamming while simultaneously causing more avalanches. On the micro-scale, polymers crosslinking in situ in flow through microchannels exhibit intermittent dynamics, in which gelation, deposition, and ablation occur repeatedly and persistently. This model system might represent situations encountered in polymer flows in 3D printing applications, or, in a greatly simplified way, two of the final steps in the coagulation cascade. We map the intermittent behavior as a function of crosslinking density and gel concentration. Intriguingly, we find signatures of chaotic behavior in systems that approach regions of complete flow failure.

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