It is well known that clays dispersed in a polymer matrix decrease the permeability of all gases through that membrane. Our objective was to explore the effects on transport when a microporous layered aluminophosphate was added to a polymer matrix. The clay like layered aluminophosphate used contains sheets with 8MR ring openings in the size range of 3-4 Ã . The molecular level dispersion of this material into a polymer matrix is theorized to increase selectivity by molecular sieving. A previous study performed in our laboratory showed an increase in He/CH4 selectivity when this aluminophosphate (8MR-AlPO) was dispersed in a fluorinated polyimide. The increase in selectivity was explained as size sieving by the aluminophosphate sheets where small gas species can pass through the microstructure and large gas species have to take a tortuous path around the sheets. We performed several studies with different polymer materials in the attempt to make composite membranes that corroborated the previously seen increases in gas selectivity. In some cases different surfactants were used to swell 8MR-AlPO. In the first set of studies the methods used to produce the fluorinated polyimide composites were repeated using polydimethyl siloxane (PDMS), a copolymer of a fluorinated polyimide and PDMS, polysulfone, Matrimid, and cellulose acetate as the matrix materials. In general gas permeation studies of these materials showed an overall decrease in permeability with increasing addition of 8MR-AlPO but no substantial increase in selectivity. In an attempt to increase the chances of exfoliating and dispersing the layered aluminophosphate, an in-situ method using poly(etherimide) (PEI) was polymerized in the presence of 8MR-AlPO was employed. Mixed matrix membranes of PEI with 5wt% 8MR-AlPO were successfully fabricated and the transport properties measured. Microscopy revealed that the composites made with the 8MR-AlPO treated with a reactive surfactant showed better dispersion than those treated with the nonreactive surfactants. The permeability of gases changed very little as the result of adding 8MR-AlPO to PEI and no substantial increase in selectivity was observed. Finally, we incorporated a similar layered aluminophosphate with larger 12MR (6-7Ã ) openings into polysulfone. These composites showed barrier behavior but no increases in selectivity. / Ph. D.

Polymer – clay nanocomposites have improved thermal, mechanical, and barrier properties when compared with the pure polymer. The objective of this study was to examine if gas separation performance could be improved by introducing a layered nanopourous aluminum phosphate with a large aspect ratio into a polymeric matrix. The aluminum phosphate has eight membered rings, which could potentially serve as a size selective medium. A hexafluorinated polyimide, 6FDA-6FpDA-8%-DABA, was used as the polymeric matrix. The polyimide and the aluminum phosphate were synthesized separately according to well documented procedures. The two materials were blended and fabricated into nanocomposite membranes. The effect of mixing temperature and percentage of layered aluminum phosphate added to the polymer on the permeation properties were examined. These factors had a direct effect on the degree of intercalation and exfoliation of the nanocomposite structure. Transmission FTIR, TEM, DMTA, and X-ray diffraction were used to characterize the morphology, structure, and composition of these nanocomposite films. The permeation properties of the nanocomposite membranes were evaluated using pure gases (He, O₂, N₂, CH₄, CO₂) at 35°C and a feed pressure of 4 atm. In general, the permeability decreased and the selectivity coefficients increased when adding 10 wt% aluminum phosphate to the polyimide. Furthermore, the membranes showed size selectivity, consistent with the pore size in the layered aluminum phosphate. / Master of Science

The process of purifying hydrogen gas using pressure swing adsorption columns heavily relies on highly efficient adsorbents. Such materials must be able to selectively adsorb a large amount of impurities, and must also be regenerated with ease. The work presented in this thesis focuses on a novel class of porous solids, metal-organic frameworks (MOFs), and their potential for use as adsorbents in hydrogen purification processes. MOFs are tuneable structures, a property that can be exploited in order to achieve the desired characteristics that are beneficial for a specific application. The design or selection of MOFs for any separation process however, relies on a thorough understanding of the relationship between a framework’s characteristics and its adsorption and selective properties. In order to identify favourable MOF characteristics for the separation of hydrogen from typical impurities a systematic molecular simulation study is performed on a large group of MOFs. Features such as the presence of short linkers, amine groups and additional aromatic rings, and a high density of linker groups are found to increase the adsorbate - framework interaction strength, and reduce the free volume available inside the pores. Both of these effects are shown to enhance MOF selectivity for impurities. Two promising materials, exhibiting desirable features, Mn MIL-53 and MIL-47, are studied further through a variety of approaches. A combination of experimental work and molecular simulations are employed in order to assess the level of flexibility in Mn MIL-53 on uptake of CO2 and CH4. An investigation of the experimental and simulation adsorption and characterization data indicates that the framework undergoes structural changes, in order to accommodate CO2 molecules, but not CH4. The form of the framework during CO2 uptake is also shown to be strongly influenced by temperature. In the case of MIL-47, adsorption isotherms simulated for a wide range of gases overpredict experimental adsorption data, leading to an in-depth investigation of non-porous effects, force field suitability, and framework rigidity. Ab initio molecular dynamics studies of MIL-47 indicate that the benzene dicarboxylate linkers rotate about their symmetry axis to reach more energetically favourable configurations, an effect responsible for the discrepancies between simulated and experimental isotherms. The effect of MOF flexibility on adsorption is further highlighted in a study of Sc2BDC3, a material able to undergo structural changes in order to accommodate a variety of adsorbates. Molecular simulations show that structural changes in the framework are responsible for the creation of additional CO2 adsorption sites as pressure is increased, whereas methanol adsorption sites occupied at extreme pressure are stabilized by the formation of hydrogen bonds. Finally, the exceptionally robust UiO-66(Zr) and UiO-67(Zr) families of MOFs are analysed using a multi-scale simulation study combining molecular level and process-scale computational work, seeking to compare the materials to commercial adsorbents, and assess whether they are suitable for H2 purification through pressure swing adsorption (PSA). Of the four MOFs studied, UiO-66(Zr)-Br is the most promising, as it significantly outperforms commercial zeolites and activated carbons in H2 purification from steam methane reformer offgas.

The recovery of the selected biological material in affinity-based separations relies on reversing the biological interaction responsible for the binding. General elution methods which are independent of the bioaffinity interaction have attracted increasing attention. The first three chapters of this thesis describe the development of a novel “click” functionalised azobenzene-based linker for affinity-independent elution protocols and the preliminary affinity studies using this linker. Ligands functionalised with a bioorthogonal propargyl label were readily attached to the terminal azide of the linker using the copper(I) catalysed Huisgen cycloaddition (or "click" reaction). Following separation, the linker was cleaved under mild non-denaturing conditions using Na2S2O4. In the last three chapters a novel approach towards the synthesis of the 4-methyl proline fragment of the cytotoxic natural product bisebromoamide (a potential affinity target) is proposed. For the pyrrolidine ring construction an enamide-olefin ring-closing metathesis (RCM) approach has been attempted. The installation of the required absolute stereochemistry has been achieved using a phase-transfer catalyst for the enantioselective alkylation of Schiff bases derived from glycine esters.

Doctor of Philosophy / Department of Family Studies and Human Services / Farrell J. Webb / The current military family life is punctuated by a series of events that are not present in the lives of most Americans, most notably the stress, fear, and disruption of lives that accompany the periodic absences of one or both adults in the family. These absences fostered by deployments, challenges of readjustments, coupled with combat injuries have tremendous effects on not only the troops and their families, but also the communities that military families live in as well. This investigation examined how military assistance, family connectedness and community networks contribute to the well-being of families affected by anticipated and repeated deployments that cause family interruptions. Despite the myriad of studies on military deployments and the impact on families, there has been little focus on the spouse and children that relates to their resilience during the deployment process. Using an online national all service unit sample from military spouses (n = 185) who have children and have experienced a recent deployment (n = 153) it was possible to isolated the specific components that influenced the well-being of those affected by deployments. The Influence of Interruptions on Family Well-Being Model—which combines ideas from both the ecological systems and boundary ambiguity perspectives—was tested and utilized in this study. It was disclosed that 45% of the variance in well-being could be explained by knowing how families perceive the deployment process, military assistance, community networks, family connectedness, and how these families coped with periodic family interruptions. These data revealed that deployments have a greater impact than originally conceived and that issues addressing deployments must be placed on the national agenda, particularly where family well-being is concerned. The research findings underscore the importance of family to both the deployed personnel and the ones that they leave home. The implications from this investigation are simple and direct—there needs to be a more comprehensive program for children that employ pre-, during- and post-deployment related issues, such as adjustments to absent parents, developing better responses to the authority structure of the remaining parent, and some program focused on the immediate and long-term psychological needs of the children and their families.

Protactinium (Pa) is an actinide with chemical properties that are unique among the actinide elements. While the properties of other actinides are to a large extent understood, much of the chemistry of Pa remains a mystery. This thesis aims to illuminate new understanding of Pa chemistry through behavioral analysis using analytical techniques including liquid-liquid extraction (LL); extraction chromatography (ExC); and spectroscopic studies. Applications of radioanalytical chemistry and Pa: Through the research presented in this dissertation, we have developed a new way to separate uranium (U), thorium (Th), and Pa from complex environmental samples. The approach has been demonstrated for U-series dating of materials by alpha spectrometry. The method can be applied to geochronology, as well as to nuclear-forensic analysis of uranium-containing materials. In studies presented here, samples from a Paleolithic lake (Lake Bonneville, Utah USA) were analyzed for the radioactivity concentration of 230Th, 231Pa, 234U, 235U, and 238U by isotope dilution alpha spectrometry. Radioactivities were used to estimate of the time period of formation of the deposit from which the samples were collected. Ages were determined from the isotopics ratios; i.e., 231Pa/235U (40 ka); and 230Th/238U (39.5 ka) we found to be concordant with radiocarbon-14 dates (37 ka) obtained by collaborators at Brigham Young University. These studies inspired the development of a novel ExC resin to facilitate preparation of highly pure tracer isotope (233Pa) from a neptunium-237 (237Np) source. The material used for this development comprised 1-octanol adsorbed to a semi-porous resin material. The new approach greatly improved the yield and purity of 233Pa used for these chronometric analyses Developing an understanding of the chemistry of Pa at trace concentrations: The new-improved analytical described above led to the hypothesis that analytical separations approaches could be used to develop a more detailed understanding of Pa chemistry. Toward this goal, experiments were conducted to understand how the extraction of Pa is impacted by solution acidity [H+], anion concentration [A-; Cl-, NO3-], and extractant concentration ([2,6-dimethyl-4-heptanol, DIBC]). A full-factorial experimental design was employed to create a model that would allow for predictions in Pa behavior, as well as describe the nature of the observations. This model generated a multivariate equation that relates the distribution coefficient ([Pa] organic phase/ [Pa] aqueous phase) to each of the parameters ([H+], [A-], and [DIBC]). Further studies expanded to other alcohols (ROH) used as extractants (1-octanol, (2,6)-dimthyl-4-heptanol, and 2-ethyl-hexanol); and the results were analyzed using the slope analysis and comparative extraction studies using the model and compared to other actinide elements (Th, U, Np, americium (Am)) by both LL and ExC systems. These experiments revealed unique chemical behavior of Pa with respect to the other actinides. For example, it was found that Pa was the only actinide element to be extracted into the organic phase under acidic conditions (HCl and HNO3). Slope analysis experiments elucidated the stoichiometric identity of Pa species, with respect to the anion and extractant. Future studies will aim to identify the oxygen stoichiometry and species by X-ray absorption techniques. Investigations of the organic phase: In the final sections of this thesis, experiments are presented that are intended to determine if aggregation plays a key role in the extraction of Pa in systems containing 1-octanol and 2-ethyl-hexanol. This work is done in the absence of metal ions to control the dynamics of the organic phase, and are analyzed by tensiometry and Karl Fisher titrations with small angle X-ray scattering and molecular dynamic simulations. A key novel finding of these studies in that ROH molecules arrange in nanoscale aggregates that decrease the interfacial tension between the phases and extract a significant amount of water into the aggregates stabilized by a network of H-bonding. These studies lead to the hypothesis for future studies that Pa extraction is likely facilitated by solvation into the organic phase via ROH aggregates. The sum of the findings and observations of this dissertation provide insight into the chemical nature of Pa: (1) Novel extraction methods to obtain radiochemically pure fractions show that Pa can be efficiently extracted and separated from complex matrices to aid in chronometric analysis for geochronology or nuclear forensics; (2) Statistical modeling to develop a better understanding of the main effects of solvent extraction parameters; (3) Equilibrium analysis to improve our understanding of chemistry of Pa and how it is unique to the actinides; (4) Aggregation analysis to demonstrate a solvent centric understanding of extraction studies, these results lead to future experiments to investigate how organic phase aggregation can influence solvent extraction selectivity.

The armchair variety of single-wall carbon nanotubes (SWCNTs) is the only nanotube species that behaves as a metal with no electronic band gap and massless carriers, making them ideally suited to probe fundamental questions of many-body physics of one-dimensional conductors as well as to serve in applications such as high-current power transmission cables. However, current methods of nanotube synthesis produce bulk material comprising of a mixture of nanotube lengths, diameters, wrapping angles, and electronic types due to the inability to control the growth process at the nanometer level. As a result, measurements of as-grown SWCNTs produce a superposition of electrical and optical responses from multiple SWCNT species. This thesis demonstrates production of aqueous suspensions composed almost entirely of armchair SWCNTs using a post-synthesis separation method employing density gradient ultracentrifugation (DGU) to separate different SWCNT types based on their mass density and surfactant-specific interactions. Resonant Raman spectroscopy determines the relative abundances of each nanotube species, before and after DGU, by measuring the integrated intensity of the radial breathing mode, the diameter-dependent radial vibration of the SWCNT perpendicular to its main axis, and quantifies the degree of enrichment of bulk nanotube samples to exclusively armchair tubes. Raman spectroscopy of armchair-enriched samples of the G-band mode, which is composed of longitudinal (G-) and circumferential (G+) vibrations oscillating parallel and perpendicular to the tube axis, shows that the G- peak, long-held to be an indicator for the presence of metallic SWCNTs, appears only when electronic resonance with narrow-gap semiconducting SWCNTs occurs and shows only the G+ component in spectra containing only armchair species. Finally, by combining optical absorption measurements with nanotube composition as determined earlier via Raman scattering, peak fitting of absorption spectra indicates that interband transitions of armchair SWCNTs are strongly excitonic as shown by the highly symmetric peak lineshapes, a property normally attributed to semiconductors. Such lineshapes allow classification of armchair SWCNTs as a unique hybrid class of optical nanomaterial. Combining absorption and Raman scattering measurements establishes a distinct optical signature that describes the fundamental optical processes within armchair SWCNTs and lays the foundation for future studies of many-body photophysics and electrical applications.

This research project investigated physical aging and carbon dioxide plasticization behavior of glassy polymer films. Recent studies have shown that thin glassy polymer films undergo physical aging more rapidly than thick films. This suggests that thickness may also play a role in the plasticization and conditioning responses of thin glassy films in the presence of highly-sorbing penetrants such as CO₂. The effect of film thickness on CO₂ permeation and sorption was studied extensively through carefully defined and controlled methods that provide a basis for future study of plasticization behavior. Thin films are found to be more sensitive than thick films to CO₂ exposure, undergoing more extensive and rapid plasticization at any pressure. The response of glassy polymers films to CO₂ is not only dependent on thickness, but also on aging time, CO₂ pressure, exposure time, and prior history. Thin films experiencing constant CO₂ exposure for longer periods of time exhibit an initial large increase in CO₂ permeability, which eventually reaches a maximum, followed by a significant decrease in permeability for the duration of the experiment. Thick films, in contrast, do not seem to exhibit this trend for the range of conditions explored. For a series of different polymers, the extent of plasticization response tracks with CO₂ solubility. There is little data available for gas sorption in thin glassy polymer films. In this work, a novel method involving spectroscopic ellipsometry is used to obtain simultaneously the film thickness and CO₂ sorption capacity for thin glassy polymer films. This allows a more comprehensive look at CO₂ permeability, sorption, and diffusivity as a function of both CO₂ pressure and exposure time. Like the gas permeation data, these experiments suggest that thin film sorption behavior is substantially different than that of thick film counterparts. Dynamic ellipsometry experiments show that refractive index minima, fractional free volume maxima, and CO₂ diffusivity maxima correlate well with observed CO₂ permeability maxima observed for thin Matrimid® films. These experiments demonstrate that plasticization and physical aging are competing processes. Aging, however, dominates over long time scales. Over time, CO₂ diffusivity is most affected by these competing effects, and the evolution of CO₂ diffusivity is shown to be the main contributing factor to changes in CO₂ permeability at constant pressure. / text

No description available.

The glassy copolyimide 6FDA-DAM:DABA was investigated as a polymer backbone for membranes used in aggressive sour gas separation applications. An esterification crosslinking mechanism enabled the synthesis of materials with augmented H₂S/CH₄ selectivity and plasticization resistance. These materials make use of polyethylene glycol (PEG) crosslinking agents and are referred to as PEGMC polymers. Rigorous dense film characterization of the novel crosslinkable materials indicates that excellent H₂S/CH₄ selectivity (24) is achievable while still maintaining high CO₂/CH₄ selectivity (29) under high pressure ternary mixed gas (CO₂/H₂S/CH₄) feeds. Defect-free asymmetric hollow fiber membranes were formed and appropriate crosslinking conditions were determined, allowing for the characterization of these fibers under realistic sour gas feed conditions. Also, a PDMS post-treatment was used to give ultra-high permselectivity for aggressive feeds. Using several mixed gas feeds containing high concentrations of CO₂ and H₂S at feed pressures up to 700 psig, it is shown that the crosslinked asymmetric hollow fiber membranes developed and manufactured through this work are capable of maintaining excellent separation performance even under exceedingly taxing operating conditions. For example, CO₂/CH₄ and H₂S/CH₄ permselectivity values of 47 and 29, respectively, were obtained for a 5% H₂S, 45% CO₂, 50% CH₄ feed at 35°C with 700 psig feed pressure. An extremely aggressive 20% H₂S, 20% CO₂, 60% CH₄ mixed gas feed with 500 psig feed pressure was also used; the maximum CO₂/CH4 and H₂S/CH₄ permselectivity values were found to be 38 and 22, respectively.