Colloidal suspension flow and transport behavior in small channels by magnetic resonance microscopy
Brown, Jennifer Ruth
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The research presented addresses colloidal transport issues in small channel systems using Magnetic Resonance Microscopy techniques. In transport phenomena, the interaction between convection or deterministic motions and diffusion or random motions is important in many engineering and natural applications, especially relating to multiphase flows. Magnetic Resonance methods have the ability to separate coherent from incoherent motion, as well as measure spatially resolved velocity, probability distributions of displacement, and microstructure on the pore scale, even within a multiphase colloidal system. A dilute (f < 0.10) suspension of ~2.5 mm Brownian particles under shear flow in a 1 mm diameter glass capillary was investigated using spectrally resolved Pulsed Gradient Spin Echo techniques. The results indicate particle migration inward towards the capillary center. In addition, dispersion coefficients measured via flow-compensated Pulsed Gradient Spin Echo techniques as a function of observation time indicate the onset of irreversible dynamics with increasing total strain. Particle migration and irreversible dynamics are generally not expected to occur in dilute Brownian suspensions and are therefore not considered in the modeling of flow systems.Evidence of these effects, as indicated by the data presented, exhibits the importance of many body hydrodynamics in dilute Brownian suspensions and shows the applicability of chaos theory and non equilibrium statistical mechanics methods to model these systems. Additionally, blood, a well-studied cellular suspension with controllable aggregation properties, was studied when exposed to shear in a small gap cylindrical Couette rheometer. Shear induced particle migration in inhomogeneous shear flows creates non-uniform particle concentrations and cell depletion near the walls of the flow chambers. Non-uniform particle concentrations affect the overall flow characteristics of the suspension and create spatial variation of effective material properties, such as apparent viscosity. Understanding erythrocyte migration away from vessel walls is useful for identifying physiological transport mechanisms, designing filtration devices and designing microfluidic based sensors for blood. As a non-invasive and non-destructive technique with the ability to probe time and length scale displacements non-invasively, Magnetic Resonance Microscopy provides a unique perspective on the study of complex and opaque colloidal suspension flow.