Mixing, Migration, and Structure of Suspensions in Pressure-Driven Flows

Lehigh University, Bethlehem PA

Investigators

Abstract

Suspensions of a moderate particle volume fraction tend to demix in nonlinear shear. Although this effect has been studied extensively in simple flows to determine how suspension rheology results in migration, few studies have considered how migration occurs in more complicated flows. Migration in industrial processes has long complicated process development and has become increasingly important as researchers strive to process and analyze blood and other biological suspensions in complicated BioMEMS flows. The objectives of this research are to broaden our fundamental understanding of flowing suspensions by considering how the fundamental symmetries within flows interplay with the underlying suspension structure. In 1D, 2D and 3D microchannel flows commonly used in BioMEMS, the competition between suspension demixing via shear migration resulting from multibody hydrodynamic interactions and chaotic advection generated within microchannels designed to enhance mixing will be investigated. Direct measurement of flow and concentration profiles will be performed using high speed 3D confocal laser scanning microscopy (CLSM). This technique, coupled with a flow-stop-scan protocol, allows direct measurement of suspension structural anisotropy that generates the normal stresses that result in migration. These studies will be extended to examination of technologically relevant fluids, including polydisperse suspensions, electrostatic-stabilized suspensions, suspensions in viscoelastic media, and whole blood. Because flow, migration, and local structure is determined directly using CLSM, the effect of the addition of monosized suspension on cell migration and rouleau formation can be examined. In addition, continuum models will be used to explore the coupling between suspension migration and the underlying topology in chaotic flows. The intellectual merits and transformative aspects of this study include the development of directly measuring suspension structure and demonstrating the coupling between chaos and segregation in flowing suspensions. The broader impacts of this research include a new paradigm of using chaotic advection as a template for self-organization in suspensions that could revolutionize suspension processing from the microscale to industrial-scale, a potential new platform for whole blood fractionation and detection, and integration of graduate, undergraduate, middle school hands-on and web-based learning of the broader field of particle technology. Specifically, an Image of the Week website that presents the results of this research and university-wide microscale and nanoscale research to a broader community will be developed. Likewise, in order to introduce the broader subject of particle technology to early scientists, collaboration with a local middle school to develop a hands-on learning module for exploring granular media will engage students from low social economic status and otherwise underrepresented minority groups within engineering and the sciences.