Joseph D. Seymour

An earth’s field nuclear magnetic resonance apparatus suitable for pulsed gradient spin echo measurements of self-diffusion under Antarctic conditions

We describe an earth’s field nuclear magnetic resonance apparatus which can be used to carry out pulsed gradient spin echo (PGSE) diffusion measurements. The instrument is portable and incorporates automated process control, allowing direct measurement of the Larmor precession. The use of a common clock for pulse sequencing, excitation pulse synthesis, and detection, results in a phase stability sufficient for accurate signal averaging. The analysis of PGSE data under the conditions of a weak detection field is discussed and measurements of diffusion are presented under both New Zealand and Antarctic conditions. The Antarctic results include an example of restricted diffusion of brine water in McMurdo Sound sea ice.

A nuclear magnetic resonance study of Antarctic sea ice brine diffusivity

We have measured the diffusive motion of water molecules in the brine inclusions of Antarctic sea ice using a specially constructed nuclear magnetic resonance (NMR) apparatus. The method relies on the use of pulsed magnetic field gradients in precise analogy to well established laboratory procedures. One version of the apparatus utilised core samples extracted from the ice sheet which were subsequently analysed on site while a later version utilised a probehead which was inserted into the ice sheet, thus minimising any sample perturbation. The diffusive motion of water molecules in the brine inclusions is found to be strongly anisotropic, and, over short length scales, exhibits a rapidity greatly in excess of that expected for thermal equilibrium Brownian behaviour, an effect which we attribute to convective transport.

Turbulent pipe flow studied by time-averaged NMR imaging : measurements of velocity profile and turbulent intensity

A time-averaged method to obtain quantitative measurements in turbulent flow by phase flow encoding NMR imaging is introduced. With this method time-averaged velocity profiles and turbulence intensities can be determined. Time-averaged velocity profiles for pipe flow of water driven by a constant pressure gradient at Reynolds numbers from 1200 to 9400 were visualized. A precise correlation between the pixel intensity of the time-averaged NMR flow image and the local turbulence intensity of the flow is derived. The measured turbulence intensities are in agreement with published data obtained using other experimental methods.

Biopolymer and Water Dynamics in Microbial Biofilm Extracellular Polymeric Substance

Nuclear magnetic resonance (NMR) is a noninvasive and nondestructive tool able to access several observable quantities in biofilms such as chemical composition, diffusion, and macroscale structure and transport. Pulsed gradient spin echo (PGSE) NMR techniques were used to measure spectrally resolved biomacromolecular diffusion in biofilm biomass, extending previous research on spectrally resolved diffusion in biofilms. The dominant free water signal was nulled using an inversion recovery modification of the traditional PGSE technique in which the signal from free water is minimized in order to view the spectra of components such as the rotationally mobile carbohydrates, DNA, and proteins. Diffusion data for the major constituents obtained from each of these spectral peaks demonstrate that the biomass of the biofilm contains both a fast and slow diffusion component. The dependence of diffusion on antimicrobial and environmental challenges suggests the polymer molecular dynamics measured by NMR are a sensitive indicator of biofilm function.

NMR velocity phase encoded measurements of fibrous suspensions

Nuclear magnetic resonance (NMR) imaging is a noninvasive technique that allows velocity measurement in systems where classical techniques are not suitable due either to opacity or the presence of a solid phase. NMR velocity phase encode measurements for the flow of fiber suspensions yield quantitative data for the average flow field in the suspensions and qualitative information on the microscopic nature of the flow. Bulk translational motion causes modulation of the phase of the sample magnetization which provides information on the average velocity field within the sample. Motions on spatial and time scales that are small relative to the measurement scales cause damping of the magnetization, as reflected by signal attenuation.

Permeability of a growing biofilm in a porous media fluid flow analyzed by magnetic resonance displacement-relaxation correlations

Biofilm growth in porous media is difficult to study non‐invasively due to the opaqueness and heterogeneity of the systems. Magnetic resonance is utilized to non‐invasively study water dynamics within porous media. Displacement‐relaxation correlation experiments were performed on fluid flow during biofilm growth in a model porous media of mono‐dispersed polystyrene beads. The spin–spin T2 magnetic relaxation distinguishes between the biofilm phase and bulk fluid phase due to water–biopolymer interactions present in the biofilm, and the flow dynamics are measured using PGSE NMR experiments. By correlating these two measurements, the effects of biofilm growth on the fluid dynamics can be separated into a detailed analysis of both the biofilm phase and the fluid phase simultaneously within the same experiment. Within the displacement resolution of these experiments, no convective flow was measured through the biomass. An increased amount of longitudinal hydrodynamic dispersion indicates increased hydrodynamic mixing due to fluid channeling caused by biofilm growth. The effect of different biofilm growth conditions was measured by varying the strength of the bacterial growth medium. Biotechnol. Bioeng. 2013; 110: 1366–1375.

Pulsed gradient spin echo nuclear magnetic resonance measurements of hydrodynamic instabilities with coherent structure: Taylor vortices

Pulsed gradient spin echo (PGSE) nuclear magnetic resonance (NMR) is applied to the characterization of hydrodynamic instabilities. It is demonstrated theoretically and experimentally that for Taylor vortex flow in a Couette cell the PGSE NMR data is coherently modulated in an interference pattern dependent upon the vortex size, or wavelength, and velocity intensity. Spatially resolved NMR velocity images of all three velocity components for water in supercritical Taylor number flow and NMR velocity image data of the axial disturbance velocity for pentane at three supercritical values of the Taylor number are presented. For the short column used the NMR velocity data clearly show axial asymmetry with maximum velocities and the center (eye) of the vortex drawn toward the radial outflow boundary.

NMR measurement of hydrodynamic dispersion in porous media subject to biofilm mediated precipitation reactions.

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.

Nuclear magnetic resonance measurement of shear-induced particle migration in Brownian suspensions

The shear-induced migration of colloidal particles in capillary flow has been investigated using nuclear magnetic resonance. Nuclear magnetic resonance methods have the ability to measure spatially resolved velocity and probability distributions of displacement within a multiphase colloidal system. For a suspension of ∼2.49 μm Brownian model hard spheres under shear flow in a 1 mm diameter glass capillary, particle migration inward to the capillary center was found using spectrally resolved pulsed gradient spin echo techniques for a range of volume fractions. Particle migration was detected even in the dilute regime, down to ϕ<0.04. While particle migration has been measured and is expected in concentrated and noncolloidal suspensions, it has only recently been unequivocally detected in dilute Brownian suspensions.

Secondary flow mixing due to biofilm growth in capillaries of varying dimensions

Using a magnetic resonance microscopy (MRM) technique, velocity perturbations due to biofouling in capillaries were detected in 3D velocity maps. The velocity images in each of the three square capillary sizes (2, 0.9, and 0.5 mm i.d.) tested indicate secondary flow in both the x‐ and y‐directions for the biofouled capillaries. Similar flow maps generated in a clean square capillary show only an axial component. Investigation of these secondary flows and their geometric and dynamic similarity is the focus of this study. The results showed significant secondary flows present in the 0.9 mm i.d. capillary, on the scale of 20% of the bulk fluid flow. Since this is the “standard 1 mm” size capillary used in confocal microscopy laboratory bioreactors to investigate biofilm properties, it is important to understand how these enhanced flows impact bioreactor transport. Biotechnol. Bioeng. 2009;103: 353–360.