Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Nuclear magnetic resonance microscopy of NAFION-117 proton exchange polymer membranes(Montana State University - Bozeman, College of Engineering, 2004) Howe, Daniel Trusler; Chairperson, Graduate Committee: Joseph SeymourAs the combustion of fossil fuels for the generation of energy and transportation becomes more expensive, of limited supply, and environmentally unsound, the development of viable fuel cell alternatives becomes more important. A comprehensive understanding of the proton exchange membranes (PEM's) used as electrolytes in certain types of fuel cells will play a major role in bringing the cost and reliability of PEM fuel cell systems down to a competitive level with traditional fossil fuel methods. Magnetic resonance microscopy (MRM) is well suited to the study of these membranes because it is non-invasive, and can spatially resolve material structure and give data on transport phenomena such as diffusion that cannot be determined by other methods. The goal of this research was to use magnetic resonance microscopy to study solvent mobility levels within the polymer membranes via spin-spin, T2, magnetic relaxation and diffusion mapping. The molecular mobility can quantify membrane swelling and spatial heterogeneity of the membrane material. A key aim of the research is to correlate these findings with previous bulk MRM studies of solvent within polymer membranes. Prior bulk MRM studies of solvent molecular mobility at different hydration levels were unable to study the membranes fully submersed in solvents, as the free solvent signal would dominate the nuclear magnetic resonance (NMR) signal from the solvent within the membrane. In this study spatial resolution of the MRM data provides the means to study fully saturated membranes, a condition of interest since the degree of hydration is related to membrane operational efficiency. The material homogeneity of the polymer in the thickness and surface directions of the membrane, an important factor in the reliable performance of fuel cells, was studied via T2 mapping. Nafion®-117 was the proton exchange membrane studied because it is currently the most popular electrolyte used in the PEM fuel cell industry and several bulk MRM studies have been conducted. Results indicate that both solvent mobility and membrane swelling are highly dependant on the concentration of methanol used to prepare the samples, as seen in the bulk studies, and that solvent mobility can vary on the 20 micron level within the polymer in both the thickness and surface directions. This research establishes MRM as an important tool for the study of individual proton exchange polymer membrane samples and provides a basis for extension to the study of membranes during operation.Item Magnetic resonance microscopy studies of biofilms : diffusion, hydrodynamics and porous media(Montana State University - Bozeman, College of Engineering, 2009) Hornemann, Jennifer Ann; Chairperson, Graduate Committee: Sarah L. Codd; Joseph D. Seymour (co-chair)Due to the complicated nature of studying living bacterial communities, Magnetic Resonance Microscopy (MRM) is a necessary tool providing unique data that is complementary to other techniques such as confocal microscopy and microelectrodes. MRM has the ability to probe an opaque system non-invasively and collect velocity measurements, imaging data, diffusion, and relaxation values and is an asset in the quest to learn how biofilms establish, grow, and die. The goal of these studies was to extend current biofilm research using MRM to enhance our understanding of transport phenomena over a hierarchy of scales, from the microscopic diffusion level to the macroscopic bulk flow. Staphylococcus epidermidis was the bacteria chosen for the biopolymer diffusion and the secondary flow studies due to its common identification in opportunistic biofilm infections. This diffusion study was the first Pulse Gradient Spin Echo (PGSE) MRM measurements of the impact of environmental and chemical challenges on the biomacromolecular dynamics in medically relevant S. epidermidis biofilm material demonstrating the ability to characterize molecular dynamics in biofilms, providing a basis for sensors which can indicate the state of the biofilm after thermal or chemical treatment and provide information to further understand the molecular level mechanisms of such treatments. The secondary flow data clearly support the conclusion that reactor size impacts studies of spatially distributed biological activity, and the idea that, scaling of transport models in biofilm impacted devices is possible but requires more study. Additionally, due to the increasing amount of CO 2 in the earth's atmosphere and the need to understand the options of sequestering this CO 2 to combat the impacts of global warming, studies were conducted to understand how biofilms grow in porous media. The resilience of Bacillus mojavensis biofilms to super critical CO 2 is documented, and thus, this bacteria was chosen. Results indicate that by varying exchange times, T 2-T 2 experiments can determine the extent of biofilm growth in an opaque porous media as demonstrated in multiple glass bead pack configurations. Using MRM as a tool to study these biofilm systems over a wide range of environmental conditions is the focus of the research presented in this dissertation.Item Colloidal suspension flow and transport behavior in small channels by magnetic resonance microscopy(Montana State University - Bozeman, College of Engineering, 2007) Brown, Jennifer Ruth; Chairperson, Graduate Committee: Joseph D. Seymour; Sarah Codd (co-chair)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.