UC Santa Barbara

Suspensions, whether natural or engineered, are encountered in nearly all physical systems involving flow. For various reasons, they are crucially important in manufacturing, water resource management, and medicine. As a result, many scientists are actively working to understand suspension flows. How do particles modify the flow? How can we separate the discrete and continuous phases? How do suspensions behave in complex or confined flows? In this thesis work, I address these questions using two different experimental platforms.

In the first half, I focus on capillary suspension flows, utilizing a dip coating platform. Dip-coating is a manufacturing technique used to apply thin films and specialized coatings to a variety of wares. When suspensions are involved, the thickness of the stagnation point below the dip-coating meniscus determines whether or not suspended particles will be entrained during the dip-coating process. For a planar substrate, we control this thickness by varying the dip-coating withdraw speed and viscosity of the suspension. Here, we extend this understanding to cylindrical substrates, and show that their curvature can be used as an additional parameter to control particle entertainment. We also demonstrate how to use these controls to separate large and small particles from a bidisperse suspension.

While dip-coating provides a low-maintenance clogging-free environment, due to it's lack of solid confinement, most other suspension systems do not posses this luxury. Indeed, clogging is a major challenge in many applications, ranging from pharmaceuticals to irrigation, resulting in a growing desire for versatile and robust clog prevention techniques. Ideally these techniques should be preventative, rather than restorative, and should avoid changing the suspension itself. Thus, in the second half of this work, I probe the relationship between clogging and hydrodynamics, specifically how a pulsatile flow environment yields different clogging dynamics than a steady flow environment. I provide a primer on pulsatile flows in microfluidic systems, which highlights various applications of pulsatile flows as well as techniques for generating them. Then I present a study which systematically characterizes the mechanisms for clog mitigation in a pulsatile environment, which depend on both the pulsatile amplitude and frequency.