Browsing by Author "Fridjonsson, E. O."

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Anomalous preasymptotic colloid transport by hydrodynamic dispersion in microfluidic capillary flow
(2014-07) Fridjonsson, E. O.; Seymour, Joseph D.; Codd, Sarah L.
The anomalous preasymptotic transport of colloids in a microfluidic capillary flow due to hydrodynamic dispersion is measured by noninvasive nuclear magnetic resonance (NMR). The data indicate a reduced scaling of mean squared displacement with time from the âŒ©z(t)^{2}âŒª_{c}âˆ¼t^{3} behavior for the interaction of a normal diffusion process with a simple shear flow. This nonequilibrium steady-state system is shown to be modeled by a continuous time random walk (CTRW) on a moving fluid. The full propagator of the motion is measured by NMR, providing verification of the assumption of Gaussian jump length distributions in the CTRW model. The connection of the data to microrheology measurements by NMR, in which every particle in a suspension contributes information, is established.
Application of PFG-NMR to study the impact of colloidal deposition on hydrodynamic dispersion in a porous medium
(2014-05) Fridjonsson, E. O.; Codd, Sarah L.; Seymour, Joseph D.
Colloidal particulate deposition affects the performance of industrial equipment, reverse osmosis membranes and sub-surface contaminant transport. Nuclear magnetic resonance (NMR) techniques, i.e. diffusion, diffraction and velocity imaging, are used to study the effect deposited colloidal particulate have on the fluid dynamics of water inside a model porous medium. Specially prepared oil-filled hard-sphere particles allow monitoring of particulate accumulation via NMR spectroscopy. Evidence of preferential spatial deposition is observed after the initial colloidal particulate deposition. Loss of spatial homogeneity is observed through NMR diffraction, while observations of the probability distributions of displacement (propagators) indicate the formation of back-bone type flow. This paper presents unique dynamic NMR data for the non-invasive non-destructive investigation of fluid transport in opaque porous media experiencing colloidal deposition.
Colloid particle transport in a microcapillary: NMR study of particle and suspending fluid dynamics
(2016-10) Fridjonsson, E. O.; Seymour, Joseph D.
Precise manipulation of the hydrodynamic interaction between particles is particularly important for operation of microfluidic devices. Shear-induced migration gives rise to dynamical patterns within the flow that have been observed in a range of systems. In this work NMR ‘active’ colloidal particles (a=1.25 µm) at volume fraction of 22% in an aqueous phase are flowed through a µ-capillary (R=126 µm) and the transport dynamics of the particle and suspending fluid phases are studied using dynamic NMR techniques. Simultaneous interrogation of shear rheology of the suspending fluid and particle phases of colloidal suspensions is presented. The dynamic behavior of the suspending fluid is shown to carry within it information about the structure of the colloidal particle ensembles on the time scales investigated (Δ=25 ms→250 ms) providing rich experimental data for further investigation and model verification. The importance of determining the particle concentration profile within μ-capillaries is explicitly demonstrated as shear induced migration causes significant concentration gradients to occur at strong flow conditions (i.e. Pep=270).
NMR measurement of hydrodynamic dispersion in porous media subject to biofilm mediated precipitation reactions
(2011-03) Fridjonsson, E. O.; Seymour, Joseph D.; Schultz, Logan N.; Gerlach, Robin; Cunningham, Alfred B.; Codd, Sarah L.
Noninvasive measurements of hydrodynamic dispersion by nuclear magnetic resonance (NMR) are made in a model porous system before and after a biologically mediated precipitation reaction. Traditional magnetic resonance imaging (MRI) was unable to detect the small scale changes in pore structure visualized during light microscopy analysis after destructive sampling of the porous medium. However, pulse gradient spin echo nuclear magnetic resonance (PGSE NMR) measurements clearly indicated a change in hydrodynamics including increased pore scale mixing. These changes were detected through time-dependent measurement of the propagator by PGSE NMR. The dynamics indicate an increased pore scale mixing which alters the preasymptotic approach to asymptotic Gaussian dynamics governed by the advection diffusion equation. The methods described here can be used in the future to directly measure the transport of solutes in biomineral-affected porous media and contribute towards reactive transport models, which take into account the influence of pore scale changes in hydrodynamics.