Open Access. Powered by Scholars. Published by Universities.®

Chemistry Commons™

Open Access. Powered by Scholars. Published by Universities.®

2001

Discipline
Institution
Keyword
Publication
Publication Type
File Type

Articles 361 - 381 of 381

Full-Text Articles in Chemistry

The Thermal Stability Of Cross-Linked Polymers: Methyl Methacrylate With Divinylbenzene And Styrene With Dimethacrylates, Fawn Marie Uhl, Galina F. Levchik, Sergei V. Levchik, Caroline Dick, John J. Liggat, C.E. Snape, Charles A. Wilkie Jan 2001

The Thermal Stability Of Cross-Linked Polymers: Methyl Methacrylate With Divinylbenzene And Styrene With Dimethacrylates, Fawn Marie Uhl, Galina F. Levchik, Sergei V. Levchik, Caroline Dick, John J. Liggat, C.E. Snape, Charles A. Wilkie

Chemistry Faculty Research and Publications

Cross-linking of polymers is frequently presumed to enhance the thermal stability of polymer systems. Methyl methacrylate has been reacted with divinylbenzene and styrene with various dimethacrylates. These systems have been characterized by gel content, swelling ratio, infrared spectroscopy, thermal analysis, TGA/FT-IR, and solid state NMR. Both systems show enhanced thermal stability and char formation. This is most pronounced in the cases of methyl methacrylate with divinylbenzene and styrene with bisphenol A dimethacrylate.

Go to article

Fire Properties Of Polystyrene-Clay Nanocomposites, Jin Zhu, Alexander B. Morgan, Frank K. Lamelas, Charles A. Wilkie Jan 2001

Fire Properties Of Polystyrene-Clay Nanocomposites, Jin Zhu, Alexander B. Morgan, Frank K. Lamelas, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polystyrene−clay nanocomposites have been prepared using a bulk polymerization technique. Three new “onium” salts have been used to prepare the nanocomposites, two are functionalized ammonium salts while the third is a phosphonium salt. By TGA/FTIR, both ammonium and phosphonium treatments have been shown to degrade by a Hofmann elimination mechanism at elevated temperatures. TGA/FTIR showed that the phosphonium treatment is the most thermally stable treatment when compared to the two ammonium salts. The nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, strength and elongation at break, as a measure of the mechanical properties, thermogravimetric analysis, and cone calorimetry. The …

Go to article

Thermal Degradation Of Pvc In The Presence Of Polystyrene, Qiang Yao, Charles A. Wilkie Jan 2001

Thermal Degradation Of Pvc In The Presence Of Polystyrene, Qiang Yao, Charles A. Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of poly(vinyl chloride) (PVC) and blends of PVC with polystyrene has been studied using thermogravimetric analysis coupled to Fourier transform infrared spectroscopy. The degradation of PVC commences at weak links by an ionic pathway, but there is evidence to suggest the presence of a radical pathway at high temperatures. While there is some chemical interaction between PVC and polystyrene, the principal mode of stabilization is a physical process.

Go to article

Studies On The Mechanism By Which The Formation Of Nanocomposites Enhance Thermal Stability, Jin Zhu, Fawn Marie Uhl, Alexander B. Morgan, Charles A. Wilkie Jan 2001

Studies On The Mechanism By Which The Formation Of Nanocomposites Enhance Thermal Stability, Jin Zhu, Fawn Marie Uhl, Alexander B. Morgan, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polystyrene−clay and polystyrene−graphite nanocomposites have been prepared and used to explore the process by which the presence of clay or graphite in a nanocomposite enhances the thermal stability of polymers. This study has been designed to determine if the presence of paramagnetic iron in the matrix can result in radical trapping and thus enhance thermal stability. Nanocomposites were prepared by bulk polymerization using both iron-containing and iron-depleted clays and graphites, and they were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and cone calorimetry. The presence of structural iron, rather than that present as an impurity, significantly increases the …

Go to article

Characterization Of Solvent-Extractable Hydrocarbons From Airborne Particulates And Street Dust Of Kuala Lumpur, Nasr Yousef M. J. Omar Jan 2001

Characterization Of Solvent-Extractable Hydrocarbons From Airborne Particulates And Street Dust Of Kuala Lumpur, Nasr Yousef M. J. Omar

Student Works (2000-2009)

The solvent-extractable hydrocarbons were identified in PM 10 airborne particles and roadside soil particles collected at eight locations in the city center and the suburb of Kuala Lumpur, Malaysia during the period from November 1998 to January 1999. Airborne particles were collected using high-volume PM1o sampler on glass fiber filters over 24 h average sampling period. After ultrasonic agitation with dichloromethane, the extracts were concentrated and fractionated on an alumina-silica column into three major fractions (aliphatics, aromatics and polar compounds). The aliphatics and aromatics fractions were then subjected to gas chromatography-mass spectrometric (GCMS) analysis. The major hydrocarbons identified in these …

Go to article

Structural, Magnetic, And Mössbauer Spectral Study Of Er₂Fe₁₇ And Its Hydrides, Fernande Grandjean, Olivier Isnard, Dimitri Hautot, Gary J. Long Jan 2001

Structural, Magnetic, And Mössbauer Spectral Study Of Er₂Fe₁₇ And Its Hydrides, Fernande Grandjean, Olivier Isnard, Dimitri Hautot, Gary J. Long

Chemistry Faculty Research & Creative Works

The structural and magnetic properties of the Er2Fe17Hx compounds, where x is 0, 1, 2, 3, and 3.8, have been investigated by means of powder x-ray diffraction, thermal and ac magnetic susceptibility measurements, and iron-57 Mössbauer spectroscopy. The Er2Fe17Hx compounds crystallize in the hexagonal P63/mmc space group with the Th2Ni17-like structure, a structure which has both an iron-rich stoichiometry and disorder of the erbium and iron-iron 4f-4f dumbbell sites. The increase in the lattice parameters, the magnetic ordering temperature, the saturation magnetization, and the …

Go to article

Spectrophotometric Determination Of Propranolol As Cu(Ii), Ni(Ii) And Co(Ii) Dithiocarbamate Complexes, Ayşegül Gölcü, Mustafa Dolaz, Selahatti̇n Seri̇n Jan 2001

Spectrophotometric Determination Of Propranolol As Cu(Ii), Ni(Ii) And Co(Ii) Dithiocarbamate Complexes, Ayşegül Gölcü, Mustafa Dolaz, Selahatti̇n Seri̇n

Turkish Journal of Chemistry

A spectrophotometric method was developed for the determination of the beta adrenergic blocking drug propranolol. The method was based on the formation of Cu(II), Ni(II) and Co(II)-dithiocarbamate complexes from the secondary amine group of propranolol with carbondisulfide (CS_{2}) and the acetate salts of the metals in ammonia medium. The method was applied to the analysis of propranolol tablets and the results were statistically compared with those obtained by the official method using t- and F-tests. There was no significant difference between the mean values and the precisions of the two methods at the 95% confidence level.

Go to article

A Facile And Efficient Method For The Rearrangement Of Aryl-Substituted Epoxides To Aldehydes And Ketones Using Bismuth Triflate, Ram Mohan, Kaushik Bhatia, Kyle Eash, Nicholas Leonard, Matthew Oswald Jan 2001

A Facile And Efficient Method For The Rearrangement Of Aryl-Substituted Epoxides To Aldehydes And Ketones Using Bismuth Triflate, Ram Mohan, Kaushik Bhatia, Kyle Eash, Nicholas Leonard, Matthew Oswald

Scholarship

Aryl-substituted epoxides undergo smooth rearrangement in the presence of 0.01–0.1 mol% Bi(OTf)3•xH2O. The rearrangement is regioselective with aryl-substituted epoxides, and products arise from cleavage of the benzylic C―O bond. The highly catalytic nature of this method coupled with the fact that the reagent is relatively non-toxic, easy to handle and inexpensive make it an attractive alternative to more corrosive and toxic Lewis acids, such as BF3•Et2O, currently used to effect epoxide rearrangements.

Go to article

The Discovery-Oriented Approach To Organic Chemistry. 5. Stereochemistry Of E2 Elimination: Elimination Of Cis- And Trans-2-Methylcyclohexyl Tosylate, Ram Mohan, Marcus Cabay, Brad Ettlie, Adam Tuite, Kurt Welday Jan 2001

The Discovery-Oriented Approach To Organic Chemistry. 5. Stereochemistry Of E2 Elimination: Elimination Of Cis- And Trans-2-Methylcyclohexyl Tosylate, Ram Mohan, Marcus Cabay, Brad Ettlie, Adam Tuite, Kurt Welday

Scholarship

The E2 elimination is one of the most important reactions in organic chemistry and is discussed in considerable detail in a sophomore organic course. We have developed a discovery-oriented lab that illustrates the stereochemistry of the E2 elimination reaction and is a good exercise in 1H NMR spectroscopy. The added element of discovery insures that student interest and enthusiasm are retained.

Go to article

Deprotection Of Ketoximes Using Bismuth(Iii) Nitrate Pentahydrate, Ram Mohan, Bryce Nattier, Kyle Eash Jan 2001

Deprotection Of Ketoximes Using Bismuth(Iii) Nitrate Pentahydrate, Ram Mohan, Bryce Nattier, Kyle Eash

Scholarship

Ketoximes undergo facile deprotection in acetone-H20 (9: 1) in the presence 01' 0.5 equivalents of Bi(N03h•5H20. Bismuth(III) nitrate is relatively non-toxic, insensitive to air and inexpensive. These features coupled with the use of a relatively nontoxic solvent system make this method an attractive alternative to existing routes for deprotection of ketoximes.

Go to article

How To Evaluate An On-Road Remote Sensor, Donald H. Stedman Jan 2001

How To Evaluate An On-Road Remote Sensor, Donald H. Stedman

Fuel Efficiency Automobile Test Publications

All on-road remote sensors or which we are aware carry out at least a measurement of the CO/CO2 ratio in the exhaust of a passing vehicle. It is possible for an interested party to carry out a quantitative evaluation of the precision of this measurement. This evaluation can be done without going to the expense and complexity of an on-road audit using a vehicle of known emissions (wet gas audit), or a vehicle designed to puff surrogate compressed gas mixtures of known ratios (dry gas audit). The measurement of exhaust CO/CO2 ratio is obtained by estimating the slope of a …

Go to article

On-Road Remote Sensing Of Automobile Emissions In The Phoenix Area: Year 2, Sajal S. Pokharel, Gary A. Bishop, Donald H. Stedman Jan 2001

On-Road Remote Sensing Of Automobile Emissions In The Phoenix Area: Year 2, Sajal S. Pokharel, Gary A. Bishop, Donald H. Stedman

Fuel Efficiency Automobile Test Publications

The University of Denver conducted a five-day remote sensing study in the Phoenix, AZ area in the fall of 1999. The remote sensor used in this study is capable of measuring the ratios of CO, HC, and NO to CO2 in motor vehicle exhaust. From these ratios, we calculate mass emissions per kg (or gallon) of fuel and the percent concentrations of CO, CO2, HC and NO in motor vehicle exhaust which would be observed by a tailpipe probe, corrected for water and any excess oxygen not involved in combustion. The system used in this study was also configured to …

Go to article

Structural, Electronic, And Magnetic Properties Of Lani₅₋ₓtₓ (T = Fe, Mn) Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James, Y. Kong Jan 2001

Structural, Electronic, And Magnetic Properties Of Lani₅₋ₓtₓ (T = Fe, Mn) Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James, Y. Kong

Physics Faculty Research & Creative Works

Structures and magnetic properties of the LaNi5-xFex and LaNi5-xMnx compounds have been investigated using neutron diffraction and first-principles tight-binding-linear-muffin-tin-orbital methods. Both neutron diffraction refinement data and total energy calculations show that the Fe and Mn atoms preferentially occupy the 3g sites in the hexagonal CaCu5-type structure. The calculated magnetic moments of Fe and Ni atoms are of 2.4-2.5μB and 0.2-0.5μB in LaNi5-xFex, respectively. The magnetic structure exhibits more localized moments at Fe atoms in LaNi5-xFex when x ≤ 1.0. Electronic structure calculations indicate …

Go to article

Electronic Structures And Magnetism Of Lani₅₋ₓfeₓ Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James Jan 2001

Electronic Structures And Magnetism Of Lani₅₋ₓfeₓ Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James

Physics Faculty Research & Creative Works

A systematic study of the magnetic moments and hyperfine interactions of the LaNi5-xFex compounds was performed using the spin-polarized tight-binding-linear-muffin-tin-orbital methods (TBLMTO). The calculated results were compared with neutron diffraction and Mössbauer experimental data and found to be in good agreement. Fe atoms exhibit more localized magnetic moments in LaNi5-xFex when the Fe content x is lower than 1.0. The calculated magnetic moments of the Fe atoms approach values as large as 2.5μB due to the dilution effect. The strong s-d hybridization between the Ni and La atoms and the neighboring Fe in …

Go to article

Boron-Doped Homoepitaxial Diamond (100) Film Investigated By Scanning Tunneling Microscopy, Bing Xiao, Weihai Fu, Sacharia Albin, Jason Moulton, John Cooper Jan 2001

Boron-Doped Homoepitaxial Diamond (100) Film Investigated By Scanning Tunneling Microscopy, Bing Xiao, Weihai Fu, Sacharia Albin, Jason Moulton, John Cooper

Electrical & Computer Engineering Faculty Publications

Conducting epitaxial diamond films of high quality are essential for many diamond studies and diamond electronic device fabrication. We have grown boron-doped epitaxial diamond films on type Ila natural diamond (100) substrates by microwave plasma chemical vapor deposition. A gas mixture of H2/CH4 was used. Boron doping was done by placing solid sources of pure boron in the microwave plasma. Homoepitaxial films with atomic smoothness were achieved under the following growth conditions: substrate temperature 900 °C, gas pressure 40 Torr, and gas flow rates of H2/CH4 = 900/7.2 seem. The growth rate was 0.87 …

Go to article

Dynamics Of Poly(Vinyl Acetate)-D₃ On Silica, Robert D. O'Connor, Frank D. Blum, Gu Xu Jan 2001

Dynamics Of Poly(Vinyl Acetate)-D₃ On Silica, Robert D. O'Connor, Frank D. Blum, Gu Xu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Poly(vinyl acetate) (PVAc) is an important polymer in applications because of both its bulk and surface characteristics. Its chain architecture gives it a low Tg and, generally, good qualities for processing and applications, which include paints, adhesives, thin films and surface coatings. In this study, we investigate the surface dynamics of PVAc absorbed onto silica with deuterium nuclear magnetic resonance (2H NMR). For dynamics studies, 2H NMR is an excellent technique because it uses an innocuous probe that can report on correlation times (τc) from approximately 10-8 s to 10 s. We report the use of two-dimensional exchange NMR (2D-X) …

Go to article

The Synthesis Of Deuterated Arylamine Dna Adducts For Use In The Development Of An Isotope Dilution Lc/Ms/Ms Method, Philip Dmitri Olsen Jan 2001

The Synthesis Of Deuterated Arylamine Dna Adducts For Use In The Development Of An Isotope Dilution Lc/Ms/Ms Method, Philip Dmitri Olsen

LSU Doctoral Dissertations

Polycyclic aromatic amines (arylamines) are a class of chemical carcinogens that are prevalent in environmental and industrial settings. In order to study the mechanism of their toxicity a quantitative and qualitative detection method was developed to measure the C8-adenine adducts of benzidine and 2-aminofluorene in DNA samples. To do this a novel synthetic method using a palladium catalyst was developed to prepare authentic and deuterated arylamine adducts to serve as standards. These standards were then used to develop a high performance liquid chromatography, electrospray, tandem mass spectrometry, isotope dilution, detection method. To demonstrate the validity of this method two spike …

Go to article

Identification Of The Domains Of Urer, An Arac-Like Transcriptional Regulator Of The Urease Gene Cluster In Proteus Mirabilis, Carrie A. Poore, Christopher Coker, Jonathan D. Dattelbaum, Harry L.T. Mobley Jan 2001

Identification Of The Domains Of Urer, An Arac-Like Transcriptional Regulator Of The Urease Gene Cluster In Proteus Mirabilis, Carrie A. Poore, Christopher Coker, Jonathan D. Dattelbaum, Harry L.T. Mobley

Chemistry Faculty Publications

Proteus mirabilis urease catalyzes the hydrolysis of urea to CO2 and NH3, resulting in urinary stone formation in individuals with complicated urinary tract infections. UreR, a member of the AraC family, activates transcription of the genes encoding urease enzyme subunits and accessory proteins, ureDABCEFG, as well as its own transcription in the presence of urea. Based on sequence homology with AraC, we hypothesized that UreR contains both a dimerization domain and a DNA-binding domain. A translational fusion of the leucine zipper dimerization domain (amino acids 302 to 350) of C/EBP and the C-terminal half of UreR …

Go to article

Glass Transition Behavior Of Pmma Thin Films, Moses T. Kabomo, Frank D. Blum Jan 2001

Glass Transition Behavior Of Pmma Thin Films, Moses T. Kabomo, Frank D. Blum

Chemistry Faculty Research & Creative Works

In the last decade there has been an increased interest in the study of the properties of supported thin polymer films. This has been prompted by the incorporation of thin films into device applications and many other technologies. Although not without controversy, a large body of experimental work indicates departures from bulk behavior by thin films. Strong evidence from both theoretical and experimental work shows that the interaction of polymer with a substrate alters the polymer conformation and mobility. A variety of techniques has been employed to probe the mobility of thin supported polymer films. Some of these techniques indirectly …

Go to article

Graduated Segmental Mobility In Polymer Layers On Silica, Frank D. Blum, Crystal E. Porter, Wuu-Yung Lin Jan 2001

Graduated Segmental Mobility In Polymer Layers On Silica, Frank D. Blum, Crystal E. Porter, Wuu-Yung Lin

Chemistry Faculty Research & Creative Works

The behavior of thin polymer layers on oxide substrates has gotten a great deal of attention as the size of materials, and hence polymer films, has gotten smaller. Indeed, the properties of adsorbed polymers are such that they can be different from those of bulk polymers, especially when the films are very thin. A wide variety of studies have been made on adsorbed polymers and sometimes the results seem contradictory. One of the properties often measured in thin films is the apparent glasstransition temperature, Tg. In principle, many techniques are sensitive to phenomenological changes occurring around Tg and, therefore, can …

Go to article

The Coupling Of Biotechnology With Electrochemistry: Electrodenitrification Of Water Using The Enzyme Nitrate Reductase, Cyril Geyer Jan 2001

The Coupling Of Biotechnology With Electrochemistry: Electrodenitrification Of Water Using The Enzyme Nitrate Reductase, Cyril Geyer

Dissertations and Theses @ UNI

Nitrate is a worldwide contaminant that causes environmental (eutrophication) and human health (methemoglobinemia, cancers) concerns. Very few techniques are available to eliminate it from natural environment and they suffer from major drawbacks, such as production of unwanted byproducts (toxins or brine). The electrochemical reduction of nitrate on any electrode is relatively slow and catalysts or electron mediators are needed. The goal of this project was to develop a new process that could overcome these disadvantages. The project demonstrates the feasibility of using an enzyme, nitrate reductase, and a mediator, methyl viologen to transfer the electrons from the electrode to nitrate, …

Go to article

First Prev