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Full-Text Articles in Physical Sciences and Mathematics
Effects Of Molecular Architecture On Fluid Ingress Behavior Of Glassy Polymer Networks, Matthew Blaine Jackson
Effects Of Molecular Architecture On Fluid Ingress Behavior Of Glassy Polymer Networks, Matthew Blaine Jackson
Dissertations
This manuscript demonstrates the synthesis of glassy polymer network isomers to control morphological variations and study solvent ingress behavior independent of chemical affinity. Well-controlled network architectures with varying free volume average hole-sizes have been shown to substantially influence solvent ingress within glassy polymer networks. Bisphenol-A diglycidyl ether (DGEBA), bisphenol-F diglycidyl ether (DGEBF), Triglycidyl p-aminophenol (pAP, MY0510), Triglycidyl maminophenol (mAP, MY0610), and tetraglydicyl-4,4’-diamino-diphenyl methane (TGDDM, MY721) were cured with 3,3’- and 4,4’-diaminodiphenyl sulfone (DDS) at a stoichiometric ratio of 1:1 oxirane to amine active hydrogen to generate a series of network architectures with an average free volume hole-size (Vh) …
Electrochemistry Of Pani/Metal Composites In Basic Solutions, Tamthinhan Quy
Electrochemistry Of Pani/Metal Composites In Basic Solutions, Tamthinhan Quy
UNLV Theses, Dissertations, Professional Papers, and Capstones
Polyaniline (PANI) has been extensively investigated due to its unique conductivity, which is primarily dependent on the oxidation state of the material and the solution pH. PANI is an insulator when it is oxidized, and the solution pH exceeds four. Numerous attempts to extend PANI's conductivity to neutral and alkaline environments have been unsuccessful. However, our previous study has demonstrated that PANI/Pd composite is conductive and catalytically active in a basic solution, pH ∼ 12. Therefore, the conductivity and the electrochemical properties of PANI composites including PANI/Au, PANI/Pd and PANI/Pt were evaluated in basic solutions. The fundamental studies of PANI/metal …
Exploration In Metallic Nitride Fullerenes And Oxometallic Fullerenes: A New Class Of Metallofullerenes, Mary Alice Mackey
Exploration In Metallic Nitride Fullerenes And Oxometallic Fullerenes: A New Class Of Metallofullerenes, Mary Alice Mackey
Dissertations
Research groups around the world have taken an interest in the synthesis, purification, characterization, and functionalization of Metallic Nitride Fullerenes (MNFs) since their discovery in 1999. This dissertation details the discovery of another new class of molecules—Oxometallic Fullerenes (OMFs).
There are many groups worldwide doing research on MNFs, and there is a large database of published MNF research, but we have had a unique opportunity to fill a research void on OMFs as at present no one else is doing research on these molecules; herein we take molecules that we discover and perform seminal research relating to them. MNF research …
Free Volume Studies Of Various Polymeric Systems Using Positron Annihilation And Pvt-Eos Analyses, Mukul Kaushik
Free Volume Studies Of Various Polymeric Systems Using Positron Annihilation And Pvt-Eos Analyses, Mukul Kaushik
Dissertations
The glass transition phenomenon and free volume behavior below and above the glass transition temperature of various polymeric systems have been investigated. Several novel polymeric systems were considered for this study. Two generations of hyperbranched polyols, H40 and H20, were selected due to large number of hydroxyl groups on the periphery and within the bulk. The effect of hydrogen bonds and molecular weight was related with the glass transition and free volume behavior for the whole range of experimental temperature. The free volume behavior was experimentally studied using PVT and PALS to determine occupied volume, fractional free volume and number …
Development And Utilization Of Digital Image Correlation Techniques For The Study Of Structural Isomerism Effects On Strain Development In Epoxy Network Glasses, Stephen Robert Heinz
Development And Utilization Of Digital Image Correlation Techniques For The Study Of Structural Isomerism Effects On Strain Development In Epoxy Network Glasses, Stephen Robert Heinz
Dissertations
The specific aim of this dissertation is to present the findings regarding the effects of molecular structure on macroscopic mechanical performance and strain development in epoxy networks. Network molecular structure was altered through monomer isomerism and crosslink density/molecular weight between crosslinks. The use of structural isomerism provided a pathway for altering mechanical performance while maintaining identical chemical composition within the network. Isomerism was investigated primarily by the curing of diglycidyl ether of bisphenol A (DGEBA) using either the para- or meta-substituted derivatives of diaminodiphenyl sulfone (DDS). Additional insights into isomerism were gained through the investigation of networks composed of either …
Spectroscopic Methods Of Process Monitoring For Safeguards Of Used Nuclear Fuel Separations, Jamie Lee Warburton
Spectroscopic Methods Of Process Monitoring For Safeguards Of Used Nuclear Fuel Separations, Jamie Lee Warburton
UNLV Theses, Dissertations, Professional Papers, and Capstones
To support the demonstration of a more proliferation-resistant nuclear fuel processing plant, techniques and instrumentation to allow the real-time, online determination of special nuclear material concentrations in-process must be developed. An ideal materials accountability technique for proliferation resistance should provide nondestructive, realtime, on-line information of metal and ligand concentrations in separations streams without perturbing the process. UV-Visible spectroscopy can be adapted for this precise purpose in solvent extraction-based separations.
The primary goal of this project is to understand fundamental URanium EXtraction (UREX) and Plutonium-URanium EXtraction (PUREX) reprocessing chemistry and corresponding UV-Visible spectroscopy for application in process monitoring for safeguards. By …
Physical And Electrical Properties Of Trimetallic Nitride Template Endohedral Metallofullerenes And Their Polymer Nanocomposites, Hanaa Mohammed Ahmed
Physical And Electrical Properties Of Trimetallic Nitride Template Endohedral Metallofullerenes And Their Polymer Nanocomposites, Hanaa Mohammed Ahmed
Dissertations
The main objective of this study was characterization of pure metallic nitride fullerene, MNF, and MNF containing polymers to evaluate these materials as suitable devices for tunable applications. Polymer-fullerene nanocomposites consisting of linear polyurethane (PU) segments crosslinked via polyhydroxylated fullerenes (C60 and Sc3N@C80, a metallic nitride fullerene) were prepared and characterized for their mechanical and dielectric properties using dynamic mechanical analysis (DMA) and broadband dielectric spectroscopic techniques. Polyhydroxylated fullerenes C60(OH)29 and Sc3N@C80(OH)18 were synthesized in a high yield through a solid-state high sheer ball-milling procedure and were …
Self-Repairable Polymeric Networks: Synthesis And Network Design, Biswajit Ghosh
Self-Repairable Polymeric Networks: Synthesis And Network Design, Biswajit Ghosh
Dissertations
This dissertation describes the design, synthesis and development of a new class of polymeric networks that exhibit self-repairing properties under UV exposure. It consists of two parts: (a) modification and synthesis of oxetane (OXE), and oxolane (OXO) substituted chitosan (CHI) macromonomer, and (b) design, and synthesis of self-repairing polyurethane (PUR) networks consisting of modified chitosan. Unmodified CHI consisting of acetamide (-NHCOCH3), primary hydroxyl (-OH), and amine (-NH2) functional groups were reacted with OXE or OXO compounds under basic conditions in order to substitute the 1° –OH groups, and at the same time, convert -NHCOCH3 functionalities …
Precision Synthesis Of Functional Materials Via Raft Polymerization And Click-Type Chemical Reactions, Joel Diez Flores
Precision Synthesis Of Functional Materials Via Raft Polymerization And Click-Type Chemical Reactions, Joel Diez Flores
Dissertations
The need to tailor polymeric architectures with specific physico-chemical properties via the simplest, cleanest, and most efficient synthetic route possible has become the ultimate goal in polymer synthesis. Recent progress in macromolecular science, such as the discoveries of controlled/“living” free radical polymerization (CRP) methods, has brought about synthetic capabilities to prepare (co)polymers with advanced topologies, predetermined molecular weights, narrow molecular weight distributions, and precisely located functional groups. In addition, the establishment of click chemistry has redefined the selected few highly efficient chemical reactions that become highly useful in post-polymerization modification strategies. Hence, the ability to make well-defined topologies afforded by …
Photopolymerized Thiol-Ene Networks For Gas Barrier And Membrane Applications, Luke Kwisnek
Photopolymerized Thiol-Ene Networks For Gas Barrier And Membrane Applications, Luke Kwisnek
Dissertations
Gas transport and free volume properties of photopolymerized thiol-ene networks for various applications are reported. For basic, commercially-available thiol-ene formulations, oxygen permeation was strictly dependent on the difference between Ttest (room temperature for this work) and network Tg. Networks with Tg near Ttest demonstrated the lowest values of permeability, diffusivity, and solubility. A robust, high-barrier network was selected for further modification. New networks with embedded functionality were formed using a two-step approach. Thio-Michael addition of a tetrathiol to monofunctional acrylates formed new functional thiol monomers. These functional thiols were combined with an isocyanurate-based triene and …
Synthesis And Characterization Of 4,4-Prime-Distyrylbiphenyl And Its Applications In Organic Field Effect Transistors, Nestor A. Santos Jr.
Synthesis And Characterization Of 4,4-Prime-Distyrylbiphenyl And Its Applications In Organic Field Effect Transistors, Nestor A. Santos Jr.
Theses and Dissertations - UTB/UTPA
4,4’-distyrylbiphenyl (DSBP), an ambipolar small molecule with electroluminescent properties, was synthesized following two synthetic protocols. Accordingly, biphenyl was bromomethylated using a mixture of paraformaldehyde and hydrogen bromide in 20% to 60% isolated yields. Bromomethylated biphenyl was then reacted with triphenyl phosphine, or with triethyl phosphate to yield the corresponding triphenyl phosphonium bromide or triethyl phosphonate, respectively. DSBP was synthesized by reaction of the triphenyl phosphonium bromide or triethyl phosphonate with freshly distilled benzaldehyde according to the Wittig, or Horner-Wadsworth-Emmons protocols. DSBP from the Wittig reaction resulted in a mixture of cis-trans isomers, while the product from the Horner-Wadsworth-Emmons reaction yielded …
Biocompatibility Of Electrospun Polymer Nanofibers (Epns) With Nih 3t3 Cell Line And Interaction Of Quercetin With Different Flavonoids: Induction Of Phase Ii Enzymes In Vitro Cancer Cell Lines, Brenda S. Benavides
Theses and Dissertations - UTB/UTPA
Part I: In this study Electrospun nanofibers, Elasthane™ 55D, Elasthane™ 75D, Biospan®, Hydrothane™ and Lycra® were evaluated for their biocompatibility to be artificial tissue substitutes using NIH-3T3 fibroblast cells. A colorimetric based MTT dye reduction assay demonstrated that EPNs did not stop cell growth in vitro. Additionally, fluorescence confocal microscope images verified that cell adhesion occurred in the nanofibers, and cell growth on the EPNs over two weeks period was confirmed by DNA quantification.
Part II: This section of the thesis is focused on evaluation of chemopreventive properties of various phytochemicals by induction of Phase II enzymes. The interaction of …
Ruthenium-Based Olefin Metathesis Catalysts Bearing Ph-Responsive Ligands: External Control Of Catalyst Solubility And Activity, Shawna Lynn Balof
Ruthenium-Based Olefin Metathesis Catalysts Bearing Ph-Responsive Ligands: External Control Of Catalyst Solubility And Activity, Shawna Lynn Balof
Dissertations
Sixteen novel, Ru-based olefin metathesis catalysts bearing pH responsive ligands were synthesized. The pH-responsive groups employed with these catalysts included dimethylamino (NMe2) modified NHC ligands as well as N-donor dimethylaminopyridine (DMAP) and 3-(o-pyridyl)propylidene ligands. These pH-responsive ligands provided the means by which the solubility and/or activity profiles of the catalysts produced could be controlled via acid addition. The main goal of this dissertation was to design catalyst systems capable of performing ring opening metathesis (ROMP) and ring closing metathesis (RCM) reactions in both organic and aqueous media.
In an effort to quickly gain access to new …
Modification And Evaluation Of Fuel Cell Membranes, Amol Prataprao Nalawade
Modification And Evaluation Of Fuel Cell Membranes, Amol Prataprao Nalawade
Dissertations
The primary goals of this study were modification of existing Nafion® membranes and characterization of newly developed hydrocarbon-based membranes for high temperature fuel cell applications. Various Nafion®/silicate nanocomposites were formulated via in situ sol-gel reactions for tetraethylorthosilicate. Different silicate composition profiles generated across membrane cross-sections were investigated by EDAX/ESEM. Composite water uptake, proton conductivity and fuel cell performance were comparable to that of unmodified Nafion®. Tafel analysis showed better electrode kinetics for composites having more silicate in the middle and less or no silicate at electrolyte-electrode interfaces. All composites showed reduced fuel cross-over and superior …