WorldCat Identities

University of Tennessee, Knoxville Department of Chemistry

Overview
Works: 131 works in 131 publications in 1 language and 139 library holdings
Genres: Academic theses 
Roles: htt
Publication Timeline
.
Most widely held works by Knoxville University of Tennessee
Overcoming statistical error and bias in Quantum Monte Carlo : application to metal-doped helium clusters by Gary Lee Warren( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

Neutron scintillation detectors based on polymers containing lithium-6 for radiation portal monitor applications by Andrew Neil Mabe( )

1 edition published in 2013 in English and held by 2 WorldCat member libraries worldwide

The work presented herein describes an investigation of four main types of thin film polymer scintillators containing ⁶Li [lithium-6] for neutron detection: polystyrene containing ⁶LiF [lithium-6 fluoride] and a preblended fluor mixture comprising 2,5-diphenyloxazole and 1,4-bis(5-phenyloxazol-2-yl)benzene; poly(styrene-co-lithium maleate) containing salicylic acid; poly[styrene-co-lithium maleate-co-2-phenyl-5-(4-vinylphenyl)oxazole]; and poly(styrene-co-lithium 4-vinylbenzoate). A variety of chemical and physical characterizations as well as optical and scintillation characterizations were performed to guide the development of optimized compositions of each type of polymer film. The scintillation performances of optimized compositions of each type of polymer film were calibrated using GS20 lithium glass and evaluated against neutron detection and neutron/gamma-ray discrimination criteria established for radiation portal monitors. Thin films were fabricated 2 inches in diameter over a variety of thicknesses using solution-casting methods. Investigation of polystyrene-based films by photoluminescence and scintillation indicated that the optimum concentration of fluor was 5.00%. Optimum neutron/gamma-ray discrimination was achieved for 50 micrometer thick films containing 10% ⁶LiF [lithium-6 fluoride]. Two transparent lithium-containing polymers were successfully synthesized: poly(styrene-co-lithium maleate) containing salicylic acid and poly[styrene-co-lithium maleate-co-2-phenyl-5-(4-vinylphenyl)oxazole]. To the author's knowledge, the latter polymer represents the first polymer comprising the matrix, the thermal neutron capture nuclide 6Li [lithium-6], and the fluor that has been synthesized for the purpose of thermal neutron detection. The polymer poly(styrene-co-lithium 4-vinylbenzoate) could not be solvated and decomposed below its melting temperature and was thus considered not useful for this application. The polystyrene-based materials had the greatest light yields whereas the poly[styrene-co-lithium maleate-co-2-phenyl-5-(4-vinylphenyl)oxazole] material had the best neutron/gamma-ray discrimination properties. All three classes of materials can be used to satisfy the detection criteria in the current radiation portal monitor footprint by implementing a multilayer format
The development of a lutetium recovery plant by Peter Michael Smith( Book )

1 edition published in 2000 in English and held by 2 WorldCat member libraries worldwide

This research project focused on the scale-up of an industrial facility for the continuous counter-current solvent extraction (CCCSX) separation of lutetium. CCCSX involves a multistage apparatus for the mixing in each stage of two immiscible liquid phases to transfer an analyte from one phase to the other. The two phases continuously flow in opposite directions in a CCCSX system. In this research, aqueous lutetium solutions, obtained from the acid leaching of lutetium oxyorthosilicate, were mixed with kerosene solutions of phosphorus based metal extractants (e.g. mono-2-ethylhexyl-(2- ethylhexyl) phosphonic acid, MEHEHP). This system extracted the lutetium from the aqueous phase, transferring the lutetium to the organic phase. The lutetium was stripped from the organic phase by mixing this phase with an aqueous solution of highly concentrated acid. The subsequent aqueous lutetium solution was processed to produce lutetium oxide. Scale-up is a process which begins with bench-scale experiments and proceeds through pilot-scale experiments to the design of an industrial facility. Bench-scale experiments were performed to investigate the extraction characteristics of lutetium in a variety of systems. The information obtained from the bench-scale experiments was utilized in pilot-scale experiments. The pilot plant used for this research consisted of 15 interconnected mixer-settler units. This pilot plant was operated as a CCCSX system. The results of the pilot-scale experiments were used in the design of an industrial CCCSX facility with the capacity to produce 106 kg of 99.999% pure Lu₂0₃ from 127 kg of lutetium oxyorthosilicate per day. Research was also conducted on the industrialization of a technique known as precipitation stripping. Precipitation stripping involves the removal of a metal from a metal-loaded organic phase as a solid metal compound by mixing the organic phase with an aqueous solution of an appropriate precipitating agent. Precipitation stripping was applied to the lutetium CCCSX system to determine the effect of this technique of an industrial facility. It was determined that precipitation stripping can potentially reduce the volume of aqueous effluent generated by an industrial CCCSX facility by a considerable amount
Magneto-optical properties of complex oxides by Peng Chen( )

1 edition published in 2013 in English and held by 2 WorldCat member libraries worldwide

Photochemical reactions of optically active chiral and achiral organic materials by Nicie Conley Murphy( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

Sodium chlorate, NaClO₃, which crystallizes in the space group P2₁3, forms optically active crystals upon crystallization although the molecule itself is achiral. NaClO₃, has been shown to produce an asymmetric distribution of (+) and ( - ) crystals when crystallized from water while stirring. It has been discovered that beta or positron radiation can also induce asymmetric crystallization in NaClO₃ solutions. Like NaClO₃, achiral 4,4'-dimethylchalcone crystallizes in enantiomeric forms in the space group P2₁3. Kondepudi et al. provided evidence that stirred crystallizations of 4,4'-dimethylchalcone can induce a bimodal distribution of (+) and ( - ) crystals. The research presented in this dissertation offers results which show that beta radiolysis and linearly polarized and right- and left-circularly light also affect the crystallization of 4,4'-dimethylchalcone from ethyl acetate. These influences have been found to induce asymmetry in the crystals in unusual ways. The chirality of the crystals was determined via their reaction in water with pyridinium tribromide to yield the chiral compound 1,2-dibromo-4,4'-dimethylchalcone, thus allowing the chirality of the crystal to be propagated to molecular chirality. Benzil, and N, N-diisopropylbenzoylformamide are also achiral molecules that crystallize in the chiral space groups P3₁2₁, and P2₁2₁2₁, respectively. It is possible with suitable reagents in water to convert the molecules in the crystals directly into chiral molecules. Only in the case of the chalcone, however, is asymmetric induction unequivocally observed. Photoreactions initiated with circularly polarized light have been used for asymmetric synthesis, with mixed results. Reactions going through radical or ion pairs may offer a means to generate large enantiomeric excesses without degradation of the substrate. The photochemistry of racemic and resolved 2-iodooctane was previously studied by Gao et al. to give information on the dynamics of radical pair and ion pair intermediates as a function of solvent polarity and viscosity. By comparing the disappearance of the optically active substrate with its loss of optical activity, F, the fraction of the initially formed radical pair (RP) or ion pair (IP) resulting in product was determined for three solvents with differing polarities and viscosities. Gao et al. studied this effect in methanol, cyclopentane, 2-methyl-2-propanol and the gas phase. These F values will be valuable in assessing the photochemistry of 2-iodooctane in the same media with circularly polarized light. So as to determine the full effect of polarity and viscosity on the photochemistry of 2-iodooctane, the results of an extension to this study are offered here. 2-iodooctane was examined in acetonitrile and in aqueous acetonitrile solutions. The photochemistry of 2-deutrerio-2-iodoctane was also studied. The photoreaction in acetonitrile occurred almost exclusively through heterolytic reaction with less than 1.6% occurring through hemolytic reactions. A comparison of the disappearance of the optically active substrate with its loss of optical activity was done and F, the fraction of the initially formed radical pair or ion pair resulting in product was determined for solvent mixtures. It was determined that reactions in non-polar solvents proceed via radical pairs while reactions in more polar solvents proceed via either a mixture of ion pair and radical pair intermediates or exclusively through ion pairs. Reactions going through radical pairs have a greater tendency to escape the cage and react, thus larger F values are observed in these reactions. Viscosity does not correlate with the value of F, however. If the viscosity is high, fewer escape products are formed. Reactions in which the solvent polarity is high generate fewer escape products, have more intermediate returning to reactant, and have lower F values
Studies directed toward the synthesis of acylated phloroglucinols by Joseph Allen Burlison( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

The synthesis and application of [alpha]-allenyl ketones directed toward the synthesis of polycyclic polyprenylated acylphloroglucinols are described. A functionalized [alpha]-allenyl ketone was synthesized in twelve steps starting from 2-methyl-2-cyclohexenome in 24% overall yield. The [alpha]' stereocenter in the [alpha]-allenyl ketone was stereoselectively quaternized using a Tsuji allylation, Mukaiyama adol condensation sequence to afford C-1 functionalized allenyl cyclohexanone building blocks. A survey of acetals and reaction conditions for the Mukaiyama reaction suggested that 3-tert-butyldiphenylsiloxypropanal dimethyl acetal could be used, and indeed this reagent in the presence of TiCl₄ "i[OCH(CH₃)₂]₄ gave the aldol product in 63% yield. The furthest advanced intermediate was prepared from 2-methyl-2-cyclohexenone in sixteen steps in 6% overall yield
Improvement of long range order in diblock copolymer templates for nanostructure deposition by Scott Michael Fontana( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

This dissertation presents work that examines the use of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer thin films as nanoporous templates. Diblock copolymer thin films are able to microphase separate to produce microdomains on the nanometer length scale. Cylindrical domains can be perpendicularly oriented when cast as a thin film on a neutral surface. From the perpendicularly oriented cylindrical microdomains, nanoporous templates can be created. Cylindrical domain block copolymer templates can lead to the production of nanostructures, but the lack of long range ordering prevents the use of diblock copolymer template for some industrial applications. Graphoepitaxy utilizes a patterned substrate to direct epitaxial growth of long range order of the cylindrical microdomains. The role of graphoepitaxial parameters including trough width and mesa height on the ordering process of cylindrical domains in diblock copolymers thin films is monitored in this study. The quantification of order was achieved by the calculation of the order parameter from the Fast Fourier transform. An increase in order was observed in samples prepared on the mesas and in troughs of widths up to 20 [mu]m, and mesa heights in the range of 1.0 to 5.0 L₀. The role of molecular weight on the kinetics of the ordering process of cylindrical domains in diblock copolymers thin films is also examined. The kinetics of the ordering process is quantified for lower molecular weight copolymers (M[subscript n] = 63,000), but no ordering is observed for the same time scales (up to 144 hours) for larger copolymers (M[subscript n] 230,000). The reduction of the rate of formation of long-range order is attributed to the impeded diffusion of higher molecular weight polymers. These results demonstrate that there exists an upper limit on the molecular weights of diblock copolymers that can be used to create nanoscale templates with long range order, which also translates to an upper limit in pore size and spacing in these templates. While diblock copolymer templates are well established as a method to produce nanoscale arrays, the size scale of the template is limited by the molecular weight of the copolymer. For larger molecular weight polymers the diffusion rate is retarded which prevents the development of long range order. This work explores the use of solvent annealing to improve long range order of high molecular weight diblock copolymer templates. By annealing copolymer thin films in a solvent rich environment increases the diffusivity of the high molecular weight copolymer increases, which improves long range order over experimental time scales. Diblock copolymer templates are an effective method for patterning nanoscale features that are able to produce vertically aligned carbon nanofibers. We report the ability to control the size and spacing of patterned nickel nanoparticles by controlling the molecular weight of the diblock copolymer template. These nanoporous templates are able to create catalytic nickel nanoparticles with diameters as small as 18 nm with a center to center spacing of 32nm. From these catalytic nanoreactors, arrays of vertically aligned carbon nanofibers are grown via plasma enhanced chemical vapor deposition
Computational investigations of collision induced absorption by Timothy Carl Lillestolen( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

The focus of this dissertation is the computational determination of collision induced absorption spectra. We have focused on two different types of collision induced absorption: that of translational absorption and that broadening of atomic spectral lines. We have focused on generating high quality ab initio potential energy and dipole moment surfaces, and using these surfaces to calculate fully quantum mechanical absorption spectra for the systems of interest, He-Xe and Na-He. In the case of He-Xe we have calculated the potential energy and dipole moment surface using the coupled cluster single and doubles method, with a perturbative triples correction, using large correlation consistent basis sets, midbond functions, and an effective core potential on Xenon. We find our potential to be in excellent agreement with several empirical He-Xe potentials in the literature. Using these calculated surfaces, we generate fully quantum mechanical translational absorption spectra for the dimer at 298 K and 1000 K. Our results at 298 K are in good agreement with experimental results. We have also performed an analysis of the functional derivative of the absorption coefficient with respect to the dipole moment at both these temperatures, and used these derivatives to analyze to analyze differences between the spectra calculated using our ab initio potentials, and the spectra computed by other researchers. Finally, we have presented results for the transition dipole moment integrals of the pure rotational transitions of He-Xe dimers, in order to compare with future theoretical and experimental results. We have also have calculated the potential energy curves for the ground and low-lying excited states of the Na-He dimer using a multi-configurational ab initio approach and large correlation consistent basis sets. We have calculated the ground state dipole moments between the ground and excited states. We have used these surfaces to calculate a fully quantum mechanical translational absorption spectrum for the ground state of Na-He at 300 K and 1000 K, which is in reasonable agreement with previous theoretical results. We have also used these surfaces to calculate the broadening of the Na-D line due to atomic helium at 1000 K. We present results for the wings of the broadened line, which we find in reasonable agreement with other theoretical results
Factors affecting the phase separation of liquid crystals from acrylate-based polymer matrices by Nathan Joseph Crawford( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

The work presented in this dissertation covers the study of phase separation of small-molecule liquid crystals (LC's) from acrylate-based polymer matrices. These materials are used in the construction of polymer dispersed liquid crystals, or PDLC's, an emerging technology with applications ranging from privacy windows to photonic materials. The first part of this study involves the determination of the effect of increasing polymer molecular weight on the solubility of the LC 4' -octyl-4-biphenyl carbonitrile, or 8CB, in poly(methyl methacrylate), or PMMA. Optical microscopy is used to determine the equilibrium phase diagrams for blends of 8CB and PMMA with weight-average polymer molecular weights ranging from 23,000-600,000 g/mol, and differential scanning calorimetry, DSC, is used to determine the fraction of 8CB that remains trapped in the polymer matrix, or the solubility limit of 8CB. Phase diagrams show what appears to be an upper limit to the effect of polymer molecular weight. The effect of polymer molecular weight on the phase behavior is quantified by extraction of the Flory-Huggins interaction parameter from fits of the microscopy data to the Flory-Huggins theory for polymer solutions. The solubility limit data also show a limit to the effect of polymer molecular weight, and when compared to solubility limit data from previous studies that use different polymer matrices, the data supports the independence of the solubility limit from polymer composition. The second part of this work changes the emphasis of the study from the effect of polymer molecular weight to fluorination of the polymer matrix. Monomers of 2,2,2,- trifluoro ethyl methacrylate, TFEMA, and methyl methacrylate, MMA, are polymerized by atom transfer radical polymerization, or ATRP, to form copolymers with 8, 19, 25, 44, and 70% TFEMA content. The copolymers are blended with 8CB, and phase diagrams of the blends are determined by optical microscopy. As the TFEMA content of the copolymer increases, a corresponding increase in the region of immiscibility of 8CB is observed. In order to quantify the effect of increasing TFEMA content, the Flory-Huggins interaction parameters for each blend are determined from the fitting procedure used in the previous section. The final part of this thesis employs time-resolved light scattering to study the phase separation kinetics of the LC blend E7 from a polymer matrix formed by polymerization-induced phase separation, or PIPS. The light scattering experiments start with syrups that consist of two different E7 fractions, 40 and 50% by mass. The syrups are cured by a green diode laser under four different cure beam intensities. The scattering profiles for the lowest cure beam intensity exhibit behavior that supports phase separation by a spinodal decomposition mechanism
Experimental studies of intra- and intermolecular chemical structure by Cara Lynn Nygren( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

The purpose of this study was two fold. The determination of hydrogen atom positions by X-ray diffraction methods is widely underused. With advances in instrument and computing technology, the use of X-ray diffraction experiments to accurately image the electron density associated with a hydrogen bond has become feasible. Secondly, general crystallographic computing programs analyze diffraction data by employing a spherical atom model. However, no such atom can be defined solely by a sphere when bound in a molecule. The use of spherical harmonics to model diffraction data enables a more complete description of the electron density in a molecular system. The use of these types of programs has allowed a detailed analysis of a variety of both hydrogen bonded and non-hydrogen bonded system. This dissertation details the experimental information for charge density and hydrogen bonding studies. The experimental results are analyzed in depth to yield a more complete understanding of a variety of bonding motifs. In some cases, the DFT calculations were performed to augment the experimental results. A series of other experimental components are added to yield a more complete structural model of each molecular system. Chapter one presents a solid background to X-ray diffraction and the solid state. The information presented in the chapter describes the development of X-ray diffraction, various techniques and the experimental methods available to model diffraction data. Chapter one also develops the basic concepts for understanding the crystalline sold state. Chapter two gives a detailed introduction to hydrogen bonding and the use of diffraction technique to model the electron and nuclear density as well as define the distribution of these densities in a three-center four-electron bond. The first molecule analyzed is urotropine-N-oxide "ormic acid, which consists of a short, strong, symmetric hydrogen bond. Variable temperature X-ray diffraction studies were used to model the total electron density in the hydrogen bond through the use of Fourier difference maps, while neutron diffraction experiments were used to confirm the proton position in the hydrogen bond. The second system analyzed was para-iodobenzoic acid. Variable temperature X-ray diffraction experiments revealed a split-site population of the electron density associated with the proton position, as is evident by the use of difference Fourier maps. Chapter three contains the detailed charge density analysis of a material containing a short, strong, asymmetric hydrogen bond, namely cobaltocenium 3,5 bis(trifluoromethyl)phenoxide 3,5-bis(trifluoromethyl)phenol. High resolution X-ray diffraction data were collected to give insight into the chemical bonding both in the hydrogen bond as well as in the organometallic segment. Chapter four focuses on the charge density studies on a novel heterocyclic alkene, 1,2,3,4,5,6,7,8-octahydro-2a,4a,6a,8a-tetraaza-cyclopenta[fg]acenaphthylene. Accurate determination of the electron density in this system demonstrates a delocalization of the electron density on the p orbitals on nitrogen over the [pi] system. Chapter five is a detailed experimental section for all material covered in this body of work
The role of specific interactions on the dispersion and properties of carbon nanotube-polymer nanocomposites by Asif Rasheed( Book )

1 edition published in 2006 in English and held by 2 WorldCat member libraries worldwide

This dissertation presents work that exammes the role of specific chemical interactions in enhancing the dispersion of carbon nanotubes in a polymer matrix. Carbon nanotubes (CNT) possess unique mechanical, electrical and thermal properties hence can have a number of potential applications including high strength, light weight composites. Due to strong interaction among nanotubes, they stay as aggregates and hence their full potential for application is severely limited. Utilization of specific chemical interactions to induce/improve miscibility in polymer blends is well known. In this thesis, this approach is applied to carbon nanotubes polymer composites to enhance the dispersion of nanotubes in a copolymer of styrene and vinyl phenol with the idea that oxygenated functional groups on the nanotubes surface may potentially interact with the vinyl phenol groups on the polymer chain via hydrogen bonding. The first part of this thesis compares methods to oxidize carbon nanofibers by using various oxidizing agents, such as 6M HNO₃, KMnO₄, RuO₄, and a mixture of concentrated H₂SO₄/HNO₃. The efficacy of an oxidizing agent is discussed in terms of the yield of oxidized nanofibers and the amount of oxygenated functional groups generated on the nanofiber surface. Next, the dispersion of single walled carbon nanotubes (SWNT) in the matrix of a copolymer of styrene and vinyl phenol containing 0, 10, 20, 40 and 100% vinyl phenol, is examined. This study provides a method to control the dispersion of nanotubes in the polymer matrix by utilizing specific chemical interactions. The dispersion of the nanotubes was observed by optical microscopy. The dispersion of the SWNT in the polymer matrix is also quantified by optical microscopy and Raman spectroscopy. Raman spectroscopy is also used to investigate preferred interactions between the SWNTs and the copolymers via the shift in the characteristic Raman peak of the SWNTs in the composites. All composites show regions of SWNT aggregates, however the aggregate size varies with composition of the PSVPh copolymer and the amount of SWNT oxidation. Optimal dispersion of the SWNT is observed in PSVPh with 20% vinyl phenol and oxidized nanotubes, which correlates with spectroscopic evidence that indicates that this system also incorporates the most interactions between SWNT and polymer matrix. Polymer nanocomposite films containing 5 wt% single-walled carbon nanotubes (SWNT) or 5 wt% multi-walled carbon nanotubes (MWNT) with PSVPh copolymers were processed from dimethyl formamide solutions. The vinyl phenol mole ratio in the copolymers was 0, 10, 20, 30, and 40%. FTIR analysis indicates that the composites containing the copolymer with 20% vinyl phenol exhibit the maximum intermolecular interactions (hydrogen bonding) between the hydroxyl group of the vinyl phenol and the carbon nanotube functional groups. Tensile properties and electrical conductivity also are the highest in the samples containing the copolymer with 20% vinyl phenol. Thus, these results show that the optimization of the extent of intermolecular interactions between a polymer chain and a carbon nanotube results in an optimal increase in macroscopic properties. Moreover, the extent of intermolecular hydrogen bonding can be improved by optimizing the accessibility of the functional groups to participate in the non-covalent interaction. In this system, this optimization is realized by control of the amount of vinyl phenol in the copolymer, i.e., the copolymer composition. Finally, the approach of utilizing intermolecular interaction to enhance dispersion and properties was applied to composites of carbon nanofibers. Dynamic mechanical analysis (OMA) and differential scanning calorimetry (DSC) indicate that the composites prepared from oxidized nanofibers exhibit improved thermal and structural properties relative to those prepared from unoxidized nanofibers. The optimum enhancement in the mechanical and thermal properties was observed for the composite formed from oxidized nanofiber and the copolymer containing 20% vinyl phenol
Lanthanide separation using rate-controlled solvent extraction by Joey Edwin Dickson( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

Solvent extractions of many of the lanthanide ions in both single ion and mixed ion environments have been carried out. These cations were first complexed with an aqueous complexing agent and were extracted with DEHPA (di-2 ethylhexylphosphoric acid) in an organic phase (kerosene). The experiments were designed to measure the rates of extraction in the hope that separation factors might be enhanced under non-equilibrium conditions. The complexing agents tried include ethylenediaminetetraacetic acid (EDTA), tetraethylenepentamine (tetraen), nitrilotriacetic acid (NTA), and diethylenetriamine (dien). These represent a hexadentate, pentadentate, tetradentate, and tridentate agent respectively. EDTA was determined to give the best results for non-equilibrium solvent extraction. Mixed ion solvent extraction results yielded separation factors with little to no improvements over equilibrium solvent extractions in most cases. The rate of extraction decreased uniformly across the series. After numerous repetitions, the sole exception is the Er/Yb system. In this system, the non-equilibrium extraction was markedly better
Atomistic investigation of anomalous diffusion on surfaces : a deterministic approach by James Wesley Mancillas( Book )

1 edition published in 2005 in English and held by 2 WorldCat member libraries worldwide

The observation of anomalous diffusion rates on surfaces by recent experiments has renewed interest in diffusion mechanics. In order to provide a better understanding of the atomistic motions resulting in anomalous diffusion, we have investigated the diffusion dynamics of sodium on a copper surface using conservative molecular dynamics. The properties of diffusing adatoms transitioning between normal diffusive motion and anomalous motion have then been examined. Utilizing short time approximation Lyapunov exponents, stable cantori within chaotic manifolds are identified. At the periphery of these stable cantori from which anomalous diffusion originates, we have examined the transition properties of diffusive motions with abnormally long jump properties. We have verified statistically their Levy distributions, and have examined the transition life cycle of these Levy flights using Poincare section analysis
Development of high-performing polydimethylsiloxane-based membranes for carbon dioxide separation by Tao Hong( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

Analysis of primary stripper foils at the Spallation Neutron Source by an electron beam foil test stand by Eric Paul Barrowclough( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

Diamond films are used at the Spallation Neutron Source (SNS) as the primary charge exchange foils (i.e., stripper foils) of the accelerated 1 GeV (Gigaelectron volts) hydride ions. The most common type of film used is a nanocrystalline diamond film, typically 17 mm x 45 mm (millimeter) with an aerial density of 350 [mu]g/cm² (microgram per square centimeter). The diamond film is deposited on a corrugated silicon substrate using plasma-assisted chemical vapor deposition. After the growth of the diamond film, 30 mm of the silicon substrate is etched away, leaving a freestanding diamond foil with a silicon handle that can be inserted into SNS for operation. Each stripper foil is typically used for a month of operation before being replaced by another stripper foil. Since SNS is a user facility, it is very difficult and expensive to experiment with different stripper foil properties that influence the lifetime. Therefore in 2009, a test stand was designed and developed that would research various stripper foil properties and their potential performance in SNS. This test stand consisted of a thirty thousand electron volt (keV) electron gun that would be used to study stripper foil degradation and how this impacts foil lifetime. An electron gun was chosen because of its ability to replicate the thermal load on the stripper foils as well as the sheer size of the electron gun that would allow it to become a tabletop test stand. The electron gun capabilities include: current up to 5 mA (milliampere), 0.300 mm² focused spot size, and rastering in the x- and y-directions. A 30 keV and 1.6 mA/mm² (milliampere per square millimeter) electron beam deposits the same power density on a diamond foil as a 1.4 MW (megawatt) SNS beam. Rastering of the electron beam exposes a similar area of the foil as SNS beams. Experiments were conducted using the foil test stand to study: foil flutter and lifetime; effects of corrugation patterns, aerial densities, foil crystallite size (micro vs. nano), and boron doping; temperature distributions and film emissivity; and conversion rate of nanocrystalline diamond into graphite
Increasing the throughput of liquid chromatography by Joseph John Stankovich( )

1 edition published in 2014 in English and held by 1 WorldCat member library worldwide

In this manuscript the ramifications of operating very high pressure chromatographic (VHPLC) instruments at high linear velocities is discussed. Operating at higher inlet pressures causes thermal conditions inside the column to change to an extent that can alter the reproducibility and accuracy of the chromatograms produced. The experiments discussed in this dissertation were focused on the manner in which the mobile phase is eluted through the column; by either constant flow, constant pressure, operator controlled or programmed constant pressure, and conditions which keep the heat loss at the columns wall constant. Additional experiments included other practical considerations in system performance such as void spaces created from improper column connections. The results of these experiments showed that void volumes can be the leading cause of band dispersion. The metric used for all measurements were based on moment analysis, which provides a more rigorous analysis of chromatographic performance than the metrics used by the majority of the community
Novel advanced thermoplastic elastomers and solution properties of polybenzofulvene by Huiqun Wang( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Thermoplastic elastomers with thermally reversible physical crosslinks are ideal alternates to thermoset rubbers because of their recyclable and reprocessible nature. Styrenic block copolymers represent the most inexpensive block copolymers on the market. However, challenges remain in tailoring thermal and mechanical properties and enhancing upper service temperature. Living anionic polymerization (LAP) is the most powerful synthetic technique to generate well-defined polymers and block copolymers. In this dissertation, we present preparation of new functionalized macromonomers and block copolymers by LAP. Our aim is to develop TPEs with enhanced UST and tailorable properties by design of macromonomers with tunable conformation and functionalizable TPEs with ability in undergoing versatile post-polymerization modification. General aspects of styrenic TPEs, motivations, classic and state-of-the-art linear ABA triblock copolymer TPEs, followed the importance of macromonomers in preparing multigraft copolymer TPEs with exceptional elasticity are presented, in Chapter 1. High vacuum experimental techniques in LAP are also introduced. Incorporating PBF into multigraft copolymer side chains enables the thermal and mechanical properties of multigraft TPEs to be tuned by changing architecture and conformation. We describe the first synthesis of polybenzofulvene (PBF) macromonomer with styrenic end-functional groups through four different approaches by LAP and post-polymerization modification. The pros and cons of each method are discussed accordingly. In the next chapter, we discuss the correlation of microstructure, chain flexibility and glass transition temperature of PBF by studying the solution properties (specifically, characteristic ratio C∞̳). PBF with varied 1,2-/1,4 addition ratios were prepared by LAP. Their intrinsic viscosity and molecular weights were readily measured for monodisperse fractions by online SEC equipped with multiple detectors. The Burchard-Stockmayer-Fixman (BSF) model was used to derive C∞̳. The preparation and characterization of a highly functionalizable ABA block copolymer TPE with poly(4-vinyl pyridine) (P4VP) hard segments is discussed in Chapter 4. Morphological, mechanical properties and thermal properties were studied for diblock and triblock copolymers with different compositions and molecular weights. In the end, conclusions and prospects for future work are presented
Investigations into ambient ionization mechanisms : electrospray ionization and direct analysis in real time mass spectrometry by Stephen Colin Gibson( )

1 edition published in 2014 in English and held by 1 WorldCat member library worldwide

Novel methods and sensors for the analysis of trace chemicals with potential environmental applications by Samuel Mason Rosolina( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

The work in this dissertation focuses on the detection and analysis of trace chemicals in biological and environmental samples. Methods for the electrochemical detection of heavy metals Cd(II) [cadmium] and Pb(II) [lead], and the catalytic metal Pd(II) [palladium] in pharmaceutical ingredients have been optimized without the necessity of sample pretreatment. The metals can be analyzed simultaneously as well as individually, and the study includes the first known instance of the use of anodic stripping voltammetry (ASV) to detect metals in dimethyl sulfoxide (DMSO) solutions. Another method, based on ASV, has been optimized and evaluated for the purpose of mercury(II) analysis in a representative active pharmaceutical ingredient (API) and excipient. A pyridine-functionalized thin film has been fabricated to selectively preconcentrate hexavalent chromium [Cr(VI)] anions for electrochemical detection. Glassy carbon electrodes were modified through physical deposition of single-walled carbon nanotubes (SWNTs) on the electrode surface, followed by electrochemical deposition of a sol-gel containing a 2-pyridine functional group. The use of SWNTs has increased sensitivity for Cr(VI) detection in aqueous solutions, providing a detection limit of 0.3 µg L⁻¹ (micrograms per liter). Two new processes to pretreat blood samples have been developed. The treatments are based on a Fenton-like advanced oxidation process (AOP). The first method is performed with a simple convection oven over a period of five hours, while the second uses microwave irradiation for six minutes. These novel methods allow for either cost-effective pretreatment through the use of the common lab oven, or time savings through the use of the synthesis microwave. The pretreated biological samples were further analyzed via anodic stripping for quantification of copper in the whole blood. A novel, disposable, Bi (bismuth)-based colorimetric sensor was developed for the detection of toxic hydrogen sulfide (H₂S) gas. Using a simple laboratory setup to generate the H₂S in a total volume of 1.35 L (liters), the sensor was able to qualitatively detect the analyte down to 30 ppb (parts per billion), indicating its ability to be used in industrial settings and manufactured into an inexpensive product for the determination of bad breath
Polymer additives effects on structure and dynamics by Adam Eugene Imel( )

1 edition published in 2015 in English and held by 1 WorldCat member library worldwide

This dissertation presents work that expands the understanding of the effect additives have on the structure and dynamics of a polymer matrix. Polymer additives are molecules, nanoparticles or fibers that are added to a polymer to modify the properties of the host polymer. Due to the vast amount of additives available, our studies were limited to C₆₀ (C60), soft polystyrene nanoparticles, and poly(ethylene oxide). The first part of this project examined the influence that C₆₀ nanoparticles have on the assembly of polyacrylonitrile using small angle and wide-angle x-ray scattering techniques and viscometry. The addition of C₆₀ (C60) to polyacrylonitrile has little effect to the chain dimensions while in solution but shift the crystalline morphology from hexagonal packing to an orthorhombic space group. Additionally, the C₆₀ (C60) nanoparticle decreases the amount of crystallinity measured in the polymer nanocomposites. This project provides insight into the use of non-covalent interactions between a polymer and nanoparticle to produce a well-dispersed nanocomposite. The next part of the project focuses on polystyrene center of mass diffusion in the presence of soft polystyrene nanoparticles. The addition of the soft nanoparticles slowed the matrix polymer diffusion when the nanoparticles were larger or the same size as the matrix polymer chains. Although when the nanoparticles were 3 times smaller than the matrix polymer chains the nanoparticles increased the diffusion of the host polymer chains. Additionally, it was shown that the nanoparticles are not stationary, rather that the diffusion of the nanoparticles is best described by the slow mode theory of diffusion. Finally, poly(ethylene oxide) was studied as an additive to lignin solutions, which mimic the beginning production stages of lignin-based carbon fibers. The study focuses on the influence that poly(ethylene oxide) has on the self-assembly of lignin while in solution. The cylindrical structure of the lignin molecules is isotopically extended along the length of the cylinder with the addition of poly(ethylene oxide) to varying magnitudes depending on the source of the lignin. This work gives insight into the best starting conditions for lignin-based carbon fiber that can maximize the properties of the final product
 
moreShow More Titles
fewerShow Fewer Titles
Audience Level
0
Audience Level
1
  Kids General Special  
Audience level: 0.74 (from 0.60 for Analysis o ... to 0.78 for Magneto-op ...)

Alternative Names

controlled identityUniversity of Tennessee, Knoxville

controlled identityUniversity of Tennessee (Knoxville campus). Department of Chemistry

University of Tennessee, Knoxville. College of Arts and Sciences. Department of Chemistry

Languages
English (20)