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Stapf, Stefanie [Verfasser], Nicolas [Gutachter] Plumeré, and Wolfgang [Gutachter] Schuhmann. "Viologen polymers for reversible hydrogen oxidation and hydrogen generation in redox hydrogels / Stefanie Stapf ; Gutachter: Nicolas Plumeré, Wolfgang Schuhmann." Bochum : Ruhr-Universität Bochum, 2017. http://d-nb.info/1144614406/34.
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Al-Mahamad, Lamia Lafta Ghashim. "Supramolecular hydrogels and discrete structures based on metal coordination and hydrogen bonding." Thesis, University of Newcastle upon Tyne, 2017. http://hdl.handle.net/10443/3981.
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The complexation of thiolated nucleosides and nucleobases with a range of group 11 metal ions (Au(I), Ag(I), Cu(I/II), was observed to lead to the formation of hydrogels by simple inversion tests. Atomic force and electron microscopy of the xerogels showed, in many cases, the presence of fibres with lengths in the micrometre range and above; this provided evidence for the formation of coordination polymers. This thesis is concerned with the preparation, characterisation and investigation of the physical properties, mainly photoluminescence and conductivity, of these coordination polymers. 2’-Deoxy-6-thioguanosine was successfully synthesised and characterized by UV, IR, Mass, 1H-NMR, and 13C-NMR spectroscopy. The formation of coordination polymers upon reaction of Au(I), Ag(I), and Cu(II) ions with 2’-deoxy-6-thioguanosine and 6-thioguanosine in aqueous media produced hydrogels with up to 97% water+methanol by mass. The Au-6-thioguanosine gel was studied in more detail because of the interest in gold thiolate polymers and the novel properties observed for Au(I)-6-thioguanosine. Fluorescence spectroscopy observed a strong yellow emission (λmax = 606 nm) which is not present in 6-thioguanosine nor in the Au(I) solutions. The optical absorption spectrum of the coordination polymer showed a band at (λmax = 360 nm) assigned to the HOMO-LUMO transition located mainly on the S-Au-S...chain of the polymer. An induced CD band associated with the Au-S chain and an enhancement of the CD signal at shorter wavelengths, for transitions associated with the ligand, suggested the polymer has a helical structure. Further evidence was provided by analysis of the X-ray scattering pattern of the xerogel and atomic force microscopy of single fibres deposited on silicon chips. The observation of long Au(I)-6-thioguanosine fibres and strong photoluminescence suggests some delocalisation of the states associated with the Au-S chains and the possibility of electronic conductivity. This was demonstrated upon oxidative doping of Au(I)-6-thioguanosine xerogels coated over platinum microband electrodes. Treatment with iodine vapour or ([Br(C6H4)3N]SbCl6) in anhydrous acetonitrile were found to result in linear current-voltage characteristics. The temperature dependence of the conductance showed Arrhenius behaviour (over range of temperature 223 to 323 K) with an activation energy of 94 kJ mol-1. V More complex structures based on Au(I)-6-thioguanosine polymers were observed upon synthesising the polymer in the presence of duplex DNA (from calf thymus). The templating of the polymer on DNA produces long, regular, and uniform fibres with a beads-on-a-string morphology. An unusual self-assembly of Au(I)-6-thioguanosine at flat Si surfaces upon simple drop-casting, with slow evaporation was also observed. AFM images of these films showed the formation of well-defined layers, but with each layer comprising long ribbons exceeding the maximum length of the AFM scan (~15 micrometres). Ag(I)-containing hydrogels formed by reactions with 6-thioguanine, 6-mercaptopurine, and 2-thiocytosine were prepared and characterised by AFM, TEM, XPS, X-Ray, FTIR, UV-Vis, and fluorescent spectroscopy. Au(I) 2-thiocytosine was also prepared, but this produced a discrete complex rather than a gel. AFM of the Ag(I) xerogels showed the formation of very long fibres and this was confirmed by TEM images. FTIR and X-ray diffraction studies suggested the metal coordination occurred via S atoms in all three gels. The Au(I) 2-thiocytosine was found to have strong luminescence (λmax 622 nm). A new Ag(I):6-thioethero nucleoside complex was prepared containing 6-methylmercaptopurine riboside (6-MMPR) which was shown by single crystal X-ray diffraction to unexpectedly feature coordination via N7 rather than the thioether sulfur atom. Cu(II) & Co(II):6-methylmercaptopurine(6-MMP) were also synthesised as new discrete complexes. The metals binding was studied by single crystal X-ray diffraction which showed that the binding sites were N3& N9 for Cu(II) ions, and N9 for Co(II) ion in the complexes.
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Salehpour, Somaieh. "Synthesis of Stimuli-responsive Hydrogels from Glycerol." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20584.
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Due to an increased environmental awareness and thus, concerns over the use of fossil-based monomer for polymer production, there is an ongoing effort to find alternatives to non-renewable traditional monomers. This has ushered in the rapid growth in the development of bio-based materials such as green monomers and biodegradable polymers from vegetable and animal resources. Glycerol, as a renewable bio-based monomer, is an interesting candidate for sustainable polymer production. Glycerol is a renewable material that is a by-product of the transesterification of vegetable oils to biodiesel. Utilization of the excess glycerol derived from the growing biodiesel industry is important to oleochemical industries. The main objective of this thesis was to produce high molecular weight polyglycerol from glycerol and synthesize stimuli-responsive polyglycerol hydrogels. The work began with an investigation of the step-growth polymerization of glycerol to relatively high molecular weight polyglycerol using several catalysts. The catalytic reaction mechanisms were compared and the polymer products were fully analyzed. High molecular weight partially branched polyglycerol with multimodal molecular weight distributions was obtained. The polymerization of glycerol proceeded fastest with sulphuric acid as catalyst as indicated by the highest observed conversion of monomer along with the highest molecular weights. Theoretical models were used to predict the gel point and to calculate monomer functionality. High molecular weight polyglycerol was used to synthesize novel stimuli-responsive hydrogels. Real-time monitoring of step-growth polymerization of glycerol was investigated using in-line and off-line Attenuated Total Reflectance/Fourier Transform infrared (ATR-FTIR) technique.
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Habánková, Eva. "Reologické hodnocení fotogelace termocitlivých makromonomerů ve vodném prostředí." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2017. http://www.nusl.cz/ntk/nusl-316431.
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Táto práca si dáva za cieľ chemicky zasieťovať biodegradovateľný makromonomér ,-itaconyl-PLGA–PEG–PLGA vo vodnom roztoku pri teplote okolia a pri teplote tela (37 °C). ,-itaconyl-PLGA–PEG–PLGA makromonomér môže vo vode vytvárať fyzikálnu sieť vďaka hydrofóbnym interakciám medzi hydrofóbnym PLGA a hydrofilným PEG. Vďaka dvojitej väzbe kyseliny itakonovej, ktorá je k makromonoméru pripojená na jeho koncoch, sa naskytuje možnosť dodatočného chemického zasieťovania fotopolymerizáciou. Výsledkom je hybridná sieť, ktorá zvyšuje mechanickú stabilitu a životnosť hydrogélu. Na priame sledovanie formovania siete prostredníctvom zmeny mechanických vlastností bola v práci použitá fotoreológia.
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Kazek, Maciej. "Wpływ odmiany, inokulacji i hydrożelu na plonowanie i jakość nasion konwencjonalnej soi (Glycine max (L.) Merr.)." Rozprawa doktorska, Uniwersytet Technologiczno-Przyrodniczy w Bydgoszczy, 2020. http://dlibra.utp.edu.pl/Content/3214.
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Castillo, Moreno Patricia. "Développement d'un procédé de production d'hydrogène photofermentaire à partir de lactosérum." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI029/document.
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L'hydrogène est une source d'énergie précieuse en tant que source d'énergie propre et que matière première pour des innombrables industries.Les procédés biologiques de production d'hydrogène gagnent en importance en raison de leurs avantages opérationnelles et de leur polyvalence dans les substrats utilisés (y compris les eaux usées).Dans cette thèse doctoral, on a développé une méthodologie photo-fermentative de production d'hydrogène en utilisant du lactosérum en tant que substrat pour la bactérie Rhodobacter capsulatus IR3::LacZ et B10::LacZ.Ce projet a été réalisé en trois étapes, exposées dans les différents chapitres.Dans la première étape on a identifié les facteurs pertinents pour la production de l'hydrogène avec du sérum synthétique en utilisant la méthodologie de plan d'expériences.Les résultats de cet étape on a obtenu quatre modèles statistiques et on a choisi la souche IR3::LacZ pour les expériences avec du lactosérum industriel.Le rendement volumétrique maximal et le rendement produit / substrat Y P/S obtenus pour la première étape ont été de 64 ml h-1L-1 et 2,08 mol H2 mol-1 C (“C” représente la source de carbone dans ce cas lactose et lactate) pour la solution amortissant le phosphate et 43.01 ml h-1L-1 y 2.52 mol H2 mol-1 C pour la solution Kolthoff.Dans la deuxième étape, on a évalué la production d'hydrogène avec du lactosérum industriel. On a appliqué un pré-traitement de trois étapes avant d'utiliser le lactosérum comme substrat : réduction du contenu gras, déprotéinisation et stérilisation. On a obtenu un modèle validé qui décrit la production d'hydrogène seulement pour la solution amortissant de phosphate. Le rendement volumétrique maximal et le YP/S ont été de 45.93 ml h-1L-1 et de 2.29 mol H2 mol-1 C respectivement. On a déterminé que l'addition d'une étape d’homo-fermentation au processus de prétraitement es avantageuse au rendement du processus. On a obtenu une productivité volumétrique de 69.71 ml h-1L-1 et de YP/S de 2.96 mol H2 mol-1 CLa troisième étape a été la mise à l'échelle des expériences à réacteurs de 1,5 L pour sérum synthétique et de 1L pour serum industriel. On a décelé de la contamination dû à la présence d'un processus de fermentation, lequel a généré une haute production de biogas composé exclusivement par H2 y CO2 ce dernier dans une concentration non superieur à 30% (v/v).Pour ces raisons, on a conclu que conclu que le processus de production intégré, en couplant la fermentation obscure et la photo-fermentation est une option avec un énorme potentiel pour l'utilisation de lactosérum comme substrat dans la production d'hydrogène<br>Hydrogen is a valuable gas use as a clean energy source and feedstock for some industries. Biological hydrogen production processes are gaining importance due to their operational conditions and versatility in the substrates (including wastewater). A hydrogen production photo fermentative methodology was developed using cheese whey as a substrate for the bacteria Rhodobacter capsulatus strain IR3::LacZ and B10::LacZ . The project was carried out in three stages.The purpose of the first stage is to identify the relevant factors to produce hydrogen for a synthetic whey medium in a photofermentation process, using the Design of Experiments methodology. The products of this stage are four statistical models, obtained for each strain and buffer solution studied. The strain IR3::LacZ was selected for the experiments with industrial whey as substrate. The maximum volumetric yield and the product/substrate yield YP/S were 64 ml h-1L-1 and 2.08 mol H2 mol-1 C (C is the carbon source in this case lactose and lactate) and 43.01 ml h-1L-1 and 2.52 mol H2 mol-1 C for phosphate buffer and Kolthoff buffer, respectively.In the second stage the production of hydrogen with industrial whey was evaluated. A three-step pre-treatment was applied before using industrial cheese whey as substrate: fat reduction, deproteinization and sterilization. A validate statistical model describing hydrogen production was only obtained for phosphate buffer. The maximum volumetric yield and the product/substrate yield YP/S were 45.93 ml h-1L-1 and 2.29 mol H2 mol-1 C respectively. The addition of an homofermentation to the pretreatment improved the production yield, in this case a volumetric productivity of 69.71 ml h-1L-1 and a YP/S of 2.96 mol H2 mol-1 C were obtained.The third stage was the scale-up to 1.5 and 1 reactor L for synthetic whey and 1L for synthetic and industrial whey respectively. A fermentative process appeared due to a bacterial contamination, leading to a high biogas production. Biogas was exclusively composed of H2 and CO2 the last in a concentration not exceeding 30% (v/v). For this reason, it was concluded that the integrated production process coupling dark and photo fermentations) is an option with great potential for the use of whey as substrate in the production of hydrogen
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Pătru, Alexandra. "Développement de catalyseurs pour un électrolyseur alcalin H2/O2." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20012.
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Le travail de thèse présenté dans ce mémoire, est consacré à l'étude des nouveaux matériaux d'électrodes pour l'électrolyse de l'eau en milieu alcalin. L'objectif de ces études est de développer de nouveaux électrocatalyseurs à base de métaux non nobles, capables d'améliorer les cinétiques de réactions intervenant dans la décomposition de l'eau : l'évolution de l'hydrogène (HER) et l'évolution de l'oxygène (OER). L'amélioration des performances catalytiques se traduit par une diminution des surtensions de réaction et donc de l'énergie nécessaire à la production de l'hydrogène. Pour cela, nous avons choisir de réaliser des électrodes à base de nanoparticules de nickel et de cobalt pour l'HER et de nanoparticules de cobaltites de cobalt, Co3O4, pour l'OER. La mise au point de plusieurs méthodes innovantes de formulation des électrodes (dépôt par électrophorèse « réactive » et électrodes composites à base liant organique fonctionnel) a permis la réduction des surtensions des réactions. Pour une densité de courant de 100 mA cm-2, une surtension cathodique de -286 mV est nécessaire avec les électrodes composites à base de nanoparticules de nickel, -238 mV pour une électrode en Co obtenue par électrophorèse et une surtension anodique 323 mV pour une électrode composite à base de nanoparticules de Co3O4. Une étude électrochimique approfondie de l'HER a été réalisée sur différentes morphologies de nanoparticules de nickel<br>The PhD work, presented in this manuscript, is devoted to the study of new electrode materials for alkaline water electrolysis.The aim of this study is to develop new electrocatalysts based on non-noble metals. These catalysts are designed to improve the kinetics of the reactions involved in the water splitting: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The improvement of catalytic reaction results in the decrease of the overpotentials and therefore the saving of energy needed for hydrogen production. To do that, nickel and cobalt nanoparticles were used for HER, and Co3O4 nanoparticles for OER. The development of several innovative methods for electrode formulation (deposition by electrophoresis and composites electrodes based on a functional organic binder) reduced the overpotential reactions. For a current density of 100 mA cm-2, -286 mV of cathodic overpotential is needed for composites electrodes based on nickel nanoparticles, -238 mV for a Co-based electrode made by electrophoresis and 323 mV of anodic overpotential for a Co3O4 -based composite electrode. A detailed electrochemical study was made for HER on various morphologies of nickel nanoparticles
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Besson, Blondel Caroline. "Etude cinétique et mécanistique en liquéfaction directe du charbon : Impact des conditions opéartoires et dusolvant donneur d'hydrogène." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10191/document.
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L’objectif de la thèse est de comprendre et de modéliser les principaux phénomènes chimiques qui gouvernent les performances du premier réacteur, et en particulier le rôle du solvant donneur d’hydrogène, ainsi que les interactions entre charbon, solvant, hydrogène gazeux et catalyseur. L’impact des conditions opératoires telles que la température, la pression d’hydrogène, le temps de séjour ainsi que l’impact de la qualité de la charge (type de charbon et teneur en cendres) et du type de solvant ont également été évalués. Ce travail s’articule autour d’une partie expérimentale réalisée en autoclave et d’une partie modélisation basée sur un schéma réactionnel simplifié et sur un regroupement par familles chimiques. Dans un premier temps, la partie expérimentale a consisté à mettre au point une stratégie adaptée à l’étude. L’outil utilisé est un réacteur batch de type autoclave fonctionnant jusqu’à 25 MPa et 450°C qui sont des conditions opératoires classiques en hydroliquéfaction du charbon. La charge de référence utilisée est un charbon Illinois n°6, bien connu dans la littérature. Le solvant utilisé est le 1,2,3,4-tétrahydronaphtalène (tétraline) qui est une molécule naphténo-aromatique potentiellement donneuse d’hydrogène et qui a été couramment utilisée au laboratoire pour ce type d’étude. Enfin, un seul catalyseur sulfuré NiMo/Al2O3 a été testé, l’objectif de cette étude ne portant pas sur ce paramètre. Un protocole spécifique de post-traitement a été optimisé pour séparer les différentes fractions de liquéfiats produits, avant leur caractérisation. La démarche originale mise en place dans ce travail a consisté à fractionner les liquéfiats par microdistillation à bande tournante (50 plateaux théoriques) puis à fractionner la coupe résidu sous vide via des extractions par solvants. La microdistillation a ainsi permis de séparer les liquides en quatre coupes : Pi-230°C, 230-350°C,350-450°C et 450°C+, avec une bonne performance de séparation, isolant notamment la quasi totalité du solvant dans la fraction légère, performance difficile à atteindre sur des outils plus classiques. Chacune de ces coupes a été analysée en distillation simulée par chromatographie gazeuse et par analyses élémentaires CHONS. Le résidu sous vide (450°C+) a ensuite été fractionné en huiles lourdes, asphaltènes et préasphaltènes, par solubilité dans l’heptane et le toluène respectivement. Ce protocole a été appliqué à chacun des 66 essais de liquéfaction réalisés dans l’autoclave, ce qui a permis d’effectuer des bilans matières complets et d’évaluer l’impact des conditions opératoires, des interactions solvant-phase gaz-catalyseur et des différentes charges. Pour chaque bilan, le taux deconversion, les structures de rendements et les performances en hydrotraitement ont été déterminés ainsi que la répartition entre la phase gaz et le solvant dans l’hydrogénation du charbon<br>This work deals with the understanding and the modeling of coal hydroliquefaction mechanisms, more precisely the impact of operating conditions and H-donor solvent -hydrogen gas phase-catalyst interactions. Experimental tests are performed in a batch reactor by using Illinois #6 coal, tetralin and NiMo/Al2O3 catalyst. An original separation procedure is developped, combinig micor-distillation and solvent extraction. Complete mass balances allow the dtermination of conversion, product yields and product quality. Operating conditions studied are temperature (380° C-420°C), hdrogen pressure (16-22 MPa) and NiMo/Al2O3 presence. Temperatures mainly impacts the firs stage of liquefaction (also called dissolution), hydrogne pressure and catalyst the products quality. Then, tests performed with other solvents (n-undecan or diethylbenzene) and/or under N2 pressure have shown the crucial impact of solvent on the first stage of liquefaction, and and the high impact of gas phase o products quality. These experimental results allow the establishment of kinetic model. In a first step, maceral are transformed into coke, preasphaltenes and hydrotreatment products. Coke formation only depends on temperature. However, preasphaltenes and hydrotreatment products formation highly depends on solvent. Other products (asphaltenes, vacuum distillate, middle distillate, light distillate and gas) are producted from preasphaltenes
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Binti, Adrus Nadia [Verfasser], Mathias [Akademischer Betreuer] Ulbricht, and Christian [Akademischer Betreuer] Mayer. "Stimuli-Responsive Hydrogels and Hydrogel Pore-Filled Composite Membranes / Nadia Adrus. Gutachter: Christian Mayer. Betreuer: Mathias Ulbricht." Duisburg, 2012. http://d-nb.info/1021899720/34.
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Ehrenhofer, Adrian, Alice Mieting, Sascha Pfeil, et al. "An automatically rainproofing bike helmet through light-sensitive hydrogel meshes: Design, modeling and experiments." SPIE, 2020. https://tud.qucosa.de/id/qucosa%3A74218.
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For everyday cycling, one needs to carry rainproof clothing just for the case of unexpected downpours. In the present research, we present a concept for a helmet which is automatically rainproof when the rain starts. When the sun comes out, the helmet is breathable again even before it completely dries up. This functionality is provided by active hydrogel meshes. Hydrogel meshes offer great advantages due to their ability to change the aperture size with swelling and deswelling. In our current work, we present the design and modeling steps for hydrogel-layered active meshes which use (i) swelling and deswelling in hydrated state and (ii) swelling starting from the dry state. The main goal is to close the air openings of a bicycle helmet when rain starts as an automatic rainproofing. This can be achieved through the swelling of the hydrogel pNiPAAM-co-chlorophyllin in the meshes, which leads to closing when hydrated. At the same time, the light-sensitive behavior leads to opening of the apertures under direct sun exposure, i.e. when the sun appears again after the rain. We present the steps of modeling and design using the Normalized Extended Temperature-Expansion-Model (NETEM) to perform simulations in Abaqus. The model is capable of describing both the swelling of the hydrogel under light stimulus and the volume change due to hydration. It is based on the analogy between free swelling and thermal expansion and defined for nonlinear displacements. We also discuss the fabrication process of hydrogel-layered fibers and challenges in their application and simulation. As a proof of concept for hydrogel-layered meshes, we show preliminary experimental results of a poly(acrylamide)/poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAm/PAMPS) hydrogel with semi-interpenetrated network (SIPN) structure and its swelling capacities on a mesh. Starting from the active hydrogel meshes as presented in the current work, the next step can be smart textiles that harness the power of hydrogels: the adaptation to combinations of stimuli - like humidity, temperature and brightness - that define environments.
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Oborná, Jana. "Studium degradace biokompatibilních kopolymerů." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2011. http://www.nusl.cz/ntk/nusl-216802.
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This diploma thesis is focused on biocompatible polymers degradation study. Copolymers were studied based on poly(lactic-co-glycolic) acid and poly(ethylene glycol) PLGA-PEG-PLGA and further these copolymers modified with itaconic acid ITA-PLGA-PEG-PLGA-ITA. This paper investigated the influence of pH phosphate solution on the degradation of polymers. Degradation of polymers occurred at 37 °C in phosphate solution with pH 4.2, 7.4 and 9.2. High performance liquid chromatography with UV-VIS detection of diode-array type was used for quantitative determination of lactic acid and glycolic acid as the final degradation products. For qualitative identification of additional degradation products were used tandem connection liquid chromatography and mass spectrometry. Gel permeation chromatography with refractive index detector was used to determine the molecular weight decrease polymer chain after the degradation.
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Pareek, Pradeep. "Photo-crosslinked Surface Attached Thin Hydrogel Layers." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1115623310082-44480.
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Stimuli sensitive polymers and hydrogels respond with large property changes to small physical and chemical stimuli (e.g. temperature, pH, ionic strength). The bulk behavior of these polymers is widely studied and they show an isotropic swelling. However, thin hydrogel layers of polymers on a substrate show a swelling behavior, which is constrained in some way. Therefore, size, confinement, patternability, response time and transition temperature of thin hydrogel layers are the most important parameters in technological applications and this study focuses on the investigation of these above-mentioned parameters. The aim of this study involves synthesis, characterization and application of thin photo-crosslinked hydrogel layers. Dimethylmaleimide (DMI) moiety was incorporated in the polymers chains and was used to introduce photo-crosslinking by [2+2] cyclodimerization reaction in the presence of UV irradiation. The following photo-crosslinkers based on DMI group were synthesized ? - Acrylate photo-crosslinker (DMIAm) - Acrylamide photo-crosslinker (DMIAAm) - Polyol photo-crosslinker (DMIPA, DMIPACl) The conventional free radical polymerization of above listed photo-crosslinker with its respective monomer resulted in formation of photo-crosslinkable polymers of (a) HEMA, (b) DMAAm, (c) NIPAAm/DMAAm, (d) NIPAAm/Cyclam. The properties of these polymers were investigated by NMR, UV-VIS spectroscopy, GPC and SPR. Thin hydrogel layers were prepared by spin coating on gold-coated LaSFN9 glass. The covalent attachment to the surface was achieved through an adhesion promoter. Swelling behavior of the thin polymer layers was thoroughly investigated by Surface Plasmon Resonance (SPR) Spectroscopy and Optical Waveguide Spectroscopy (OWS). SPR and OWS gave a wide range of information regarding the film thickness, swelling ratio, refractive index, and volume degree of swelling of the thin hydrogel layer. For hydrophilic photo-crosslinked hydrogel layers of HEMA and DMAAm, it was observed that the volume degree of swelling was independent of temperature changes but was dependent on the photo-crosslinker mol-% in the polymer. These surface attached thin hydrogel layer exhibited an anisotropic swelling. For NIPAAm photo-crosslinked hydrogel layers with DMAAm as a hydrophilic monomer, it was observed that both transition temperature (Tc) and volume degree of swelling increases with increase in the mol-% of DMAAm. To study the effect of film thickness on Tc and volume degree of swelling, hydrogels with wide range of film thickness were prepared and investigated by SPR. These results provided vital information on the swelling behavior of surface attached hydrogel layer and showed the versatility of SPR instrument for studying thin hydrogel layers. Later part of project involved synthesis of multilayer hydrogel assembly involving a thermoresponsive polymer and a hydrophilic polymer. The combination of two layers with photo-crosslinkable DMAAm polymer as base layer and photo-crosslinkable NIPAAm polymer as top layer formulate a multilayer assembly where, the base layer only swells in response to temperature and the top layer shows temperature dependent swelling. Photo-crosslinked hydrogel layers of NIPAAm, DMAAm and HEMA shows a high-resolution patterns when irradiated by UV light through a chromium mask. At last this study focused on an important application of these hydrogel layers for cell attachment processes. Cell growth, proliferation and spreading shows a biocompatible nature of these hydrogel surfaces. Such thermoresponsive photo-crosslinkable multilayer structure forms bases for future projects involving their use in actuator material and cell-attachment processes.
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Karásková, Iva. "Využití mikroenkapsulace při vývoji hydrogelových nosičových systémů." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2017. http://www.nusl.cz/ntk/nusl-316196.
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This diploma thesis deals with application of microencapsulation techniques in development of hydrogel controlled-release systems in which the main role is played by humic acids, biopolymer chitosan, compound fertilizer NPK and 3-indoleacetic acid. This paper continues my bachelor thesis topic about utilization of polyelectrolyte complexes. The aim of this work was to develop a literature review focusing on the microencapsulation techniques and according to its results optimize the method. Microencapsulation was performed with a commercial encapsulator BUSCHI B-395 Pro and a release of individual components into a water was measured. An amout of released substances was measured by UV-VIS method and HPLC analysis. Practical part also included testing of repeated swelling and drying. It was found that suitable composition and combination of ingredients form hydrogels for further use in agriculture.
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Samanta, C. "Direct oxidation of hydrogen to hydrogen peroxide." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2004. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2423.
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Pfeifer, Christoph [Verfasser], and M. [Akademischer Betreuer] Wilhelm. "Separation Media Based on Defined Hydrogel Systems = Hydrogele als Separationsmedien auf Basis definierter Porengrößen / Christoph Pfeifer ; Betreuer: M. Wilhelm." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1216949476/34.
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Kim, Sangjoon. "The Development and Characterization of Double Layer Hydrogel for Agricultural and Horticultural Applications." University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1279116187.
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Chollet, Benjamin. "Hydrogels greffés stimulables comme actionneurs microfluidiques." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066494/document.
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Nous développons une nouvelle approche des actuateurs microfluidiques à base d’hydrogels stimulables. Contrairement aux approches précédentes, les hydrogels sont synthétisés et greffés à la paroi inférieure du microcanal avant la fermeture du système. Nous utilisons une nouvelle stratégie de synthèse pour les films d’hydrogels stimulables par chimie click thiol-ène. Les films sont obtenus par dépôt, sur des surfaces fonctionnalisées avec des thiols, d’un mélange de chaînes polymères préformées et d’un réticulant dithiol. Le greffage et la réticulation s’obtiennent simultanément par une activation thermique ou par irradiation UV. Des films et des micro-motifs sont obtenus sur une large gamme d’épaisseur allant de la centaine de nanomètres à plusieurs microns. Nous intégrons les motifs d’hydrogels stimulables dans les microcanaux pour réaliser des actionneurs. Nous étudions des actionneurs thermosensibles réalisés avec des hydrogels de poly(N-isopropylacrylamide). Avec la température, les motifs d’hydrogels gonflent ou dégonflent en absorbant/expulsant l’eau de manière réversible. L’effet est rapide (inférieur à la seconde), la transition abrupte (quelques degrés autour de la LCST à 32°C) et l’amplitude de déformation est importante (gonflement de 400%). Les micro-vannes réalisées avec cette nouvelle approche présentent de très bonnes performances et une grande durabilité. Nous avons aussi réalisé de nouveaux actionneurs reconfigurables fonctionnant comme des pièges microfluidiques. Ces actionneurs microfluidiques innovants offrent de nombreuses perspectives de par la facilité de leur mise en œuvre, leurs performances et l’intégration sur des micro-puces à haute densité<br>We develop a new method to build microactuators using stimuli-responsive hydrogels. The hydrogel is synthesized with covalent attachment to the microchannel bottom walls prior to closing the microsystem, contrarily to previous approaches. We use a new stimuli-responsive hydrogel films synthesis pathway. This synthesis is based on thiol-ene click chemistry. The formation of films is achieved by adding bifunctional thiol molecules as cross-linkers to ene-functionalized preformed polymers on thiol-modified surfaces. The cross-linking and grafting are simultaneously performed either by thermal activation or UV-irradiation. Hydrogel films and micro-patterns are easily obtained in a wide range of thickness from hundred nanometers to several microns. We show that these responsive hydrogels patterns can be integrated into microfluidics channels to build microactuators. We focus on thermo-sensitive actuators made from poly(N-isopropylacrylamide). Under temperature, hydrogel patterns reversibly swell and collapse by absorbing/expulsing water. The phase transition is rapid (lower than 1 second), abrupt (a few degrees around the LCST at 32°C) and the deformation amplitude is high (400% swelling). Microvalves obtained by this approach exhibit high performances and durability. Moreover, we develop new reconfigurable actuators functioning as microfluidic traps. These new-concept microfluidic actuators offer wide possibilities because of their ease of fabrication, their performances and their ability to be integrated into high density
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Schmidtmann, Marc. "Hydrogen transfer in hydrogen bonded solid state materials." Thesis, Connect to e-thesis, 2008. http://theses.gla.ac.uk/284/.
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Thesis (Ph.D.) - University of Glasgow, 2008.<br>Ph.D. thesis submitted to the Department of Chemistry, Faculty of Physical Sciences, University of Glasgow, 2008. Includes bibliographical references. Print version also available.
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Whittaker, Alexander. "Hydrogen future." Thesis, Blekinge Tekniska Högskola, Institutionen för tillämpad signalbehandling, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-10420.
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Hydrogen electrolysis has gone through a number of stages in research and applications. From what we can see from this report, there are several ways of producing hydrogen electrolysis, and several applications. The main purposes of this report however, is not to describe what hydrogen electrolysis is and its applications. Research and experiments has already proven that it is a functioning technology. The aim is to gather the necessary information, both theoretically and practically to be able, from a technical and business point of view analyze if this in fact is a realistic solution. To maintain a system of sustainable energy has always been an attractive market and there has existed a number of technologies that has had their share of the fame. However, most of these solutions have shown not to be viable, lucrative or technically scalable. Hence, the important issue to address is whether this is a solution worth investing in. The information gathered for the theory is based on technical reports, academic scripture and literature. All of which can be back tracked to its original source. The practical test is done by using a test kit made for universities and other institutes to better understand how hydrogen electrolysis works. The materials used are all scientifically acceptable according to the theories and technologies surrounding hydrogen electrolysis. Hence, the data gathered from the test kits are all accurate according to current research.
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Кравченко, Наталія Олександрівна, Наталия Александровна Кравченко, Nataliia Oleksandrivna Kravchenko, and R. Lopatka. "Hydrogen Energy." Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/13492.
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Hydrogen is the simplest element. An atom of hydrogen consists of only one proton and one electron. It's also the most plentiful element in the universe. Despite its simplicity and abundance, hydrogen doesn't occur naturally as a gas on the Earth - it's always combined with other elements. Water, for example, is a combination of hydrogen and oxygen (H2O).
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/13492
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Walia, Rashi. "Solid-Hydrogel Hybrid Structural Materials for Biomedical Devices and Applications." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29549.
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Hybrid combinations of hydrogels and solid materials allow a high level of functionality for devices such as tissue engineering scaffolds and soft machines. This thesis reports a versatile strategy to develop mechanically robust solid-hydrogel hybrid materials using surface embedded radicals generated through plasma immersion ion implantation (PIII) of polymeric surfaces. Acrylamide and silk hydrogels were formed on PIII activated polytetrafluoroethylene (PTFE), polyethylene (PE) and polystyrene (PS) surfaces without any external crosslinking agents or initiators. X-ray photoelectron spectroscopy (XPS) and attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectrometry confirmed the formation of the acrylamide hydrogels. The amount of hydrogel formed on the substrate increased with incubation time, monomer concentration and temperature. Stability tests indicated that 95% of the hydrogel coating was retained even after 4-months of incubation in PBS solution. Adhesive T-peel tests results demonstrating adhesion strength of the hydrogel on the PIII-treated PTFE (PIII PTFE) interface of over 300-340 N/m. Hydrogels synthesised with fibronectin enabled cell adhesion and spreading. Thesis results show that polymers functionalized with surface-embedded radicals provide excellent solid platforms for the generation of robust and functional solid-hydrogel hybrid structures for biomedical applications.
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Nováčková, Táňa. "Příprava syntetických superabsorbentů vody s obsahem huminových kyselin." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2013. http://www.nusl.cz/ntk/nusl-216990.
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This diploma thesis is focused on development and characterization of synthetic hydrogel materials containing humic acids. Based on the literature review, procedure for the preparation of synthetic superabsorbent containing humic acids was designed and optimized in order to maintain required functionality of the resulting materials, such as swelling abilities and to the controlled the release of humic substances. Very important part of this work was also characterization of superabsorbents by wide range of routine physic-chemical methods (rheometry, moisture analyzers, FT-IR). Preparation of these materials is aimed to their use in agriculture and in the environment.
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Abdelmoneim, Ibrahim Mohamed Ibrahim. "Synthesis, structural and supramolecular studies of linear and cyclic 2 1-[α/aza]-oligomers". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0159.
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La première partie de cette thèse concerne la synthèse et les études structurales de 2:1-[α/aza]-oligomères linéaires et cycliques possédant des acides aminés hydrophobes et/ou basiques. Les études RMN et IRTF ont démontré que les oligomères adopteraient des conformations de type coude β en solution. Les calculs de dynamiques moléculaires des oligomères à base de résidus lysine ont révèlé l’importance du motif aza dans le repliement de ces oligomères indépendamment de l’impact de la chaîne latérale. Les études par DRX, IRTF et RMN ont révélé que les deux hexamère cycliques (L- ou D-Phe-azaPhe-Ala)2 homo- et hétérochiraux adoptent des conformations de type coude ß en solution et à l’état solide. Ils s’organisent en structures 3D très ordonnées, stabilisées par des ponts hydrogènes et des empilements π. La deuxième partie démontre l'auto-assemblage de quelques 2:1-[α/aza]-oligomères dans certains solvants pour former des gels supramoléculaires. Le cyclooligomère hétérochiral (D-Phe-azaPhe-Ala)2 peut former des organogels. La spectroscopie et rhéologie des organogels ont révélé de bonnes stabilités thermique et mécanique avec un comportement de type solide. La MEB/MET de l'aérogel a montré une structure fibreuse 3D. De plus, deux hydrogels Fmoc-D- ou L-Phe-azaPhe-Ala-OH ont été obtenus aux pH 7.0 et 10.0. Les spectres UV et de fluorescence ont révélé une stabilisation des hydrogels par interaction π entre les groupes aromatiques. Leur analyse par CD montre que les trimères s'auto-assemblent sous forme de feuillet β en accord avec les résultats ATR/IRTF. Ainsi, leurs études rhéologiques ont révélé un comportement de type solide. La MEB des xérogels a montré une structure fibreuse. La troisième partie propose deux applications; (i) les oligomères à base de résidus lysine ont révélé de bonnes performances pour la séparation CO2/N2 dans des membranes polymères Pebax®, et (ii) le cyclohexamère hétérochiral (D-Phe-azaPhe-Ala)2 convient pour la gélification sélective avec un bon pourcentage de récupération<br>The first part of this thesis reported the synthesis and structural studies of linear and cyclic 2:1-[α/aza]-oligomers possessing hydrophobic and/or basic amino acids (lysine). NMR and FTIR results demonstrated that the oligomers could adopt β-turn conformations in solution. Molecular dynamic calculations for oligomers based lysine residues reflected the important role of the aza-motif(s) in structuring the backbones regardless the chirality and nature of the amino acids. In the other hand, X-ray, FTIR, and NMR studies showed that homo- and heterochiral cyclo-(L- or D-Phe-azaPhe-Ala)2-hexamers adopt β-turn conformations in solution and solid states. Both molecules could organize into 3D highly ordered structures stabilized by hydrogen bonds and π-stacking. The second part reflected the propensity of some 2:1-[α/aza]-oligomers to self-assemble in some solvents to form supramolecular gels. Interestingly, the heterochiral cyclo-(D-Phe-azaPhe-Ala)2-hexamer could form organogels. The spectroscopic and rheological studies of the organogels revealed good thermal and mechanical stability with solid-like behavior. SEM and TEM images of the aerogel showed fibrous structure. Furthermore, two hydrogelators, Fmoc-D- or L-Phe-azaPhe-Ala-OH, have been developed and they could achieve hydrogels at pHs 7.0 and 10.0. UV and Flu studies demonstrated that the hydrogels are supported by π-stacking between the aromatic groups. CD analysis reflected that the two hydrogelators self-assemble into β-sheet like structure in consistent with ATR-FTIR results. Both hydrogels exhibited solid-like behavior through rheological studies and the SEM analysis of the xerogels revealed fibrous structure. The third part offered two applications; (i) oligomers based lysine residues reflected good performances in CO2/N2 separation when used as additives in polymeric Pebax® membrane, and (ii) the heterochiral cyclo-(D-Phe-azaPhe-Ala)2-hexamer is suitable for phase selective gelation with good recovery percentages
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Lusson, Salomé. "Hydrogen liquefaction chain: co-product hydrogen and upstream study." Thesis, KTH, Kemiteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-290940.
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The European Green Deal declared that Europe must decarbonize to become carbon-neutral within 2050. To do so, the European Parliament emphasized hydrogen as a major tool for energy transition. In regard of current environmental challenges, liquid hydrogen has raised interest as energy carrier for energy storage and transport. Due to growing use of renewable energy sources such as solar and wind energy, intermittent sources will increase. Hydrogen production methods will become mostly intermittent with renewable energies. However, due to historical hydrogen production by steam methane reforming, liquefaction was developed at steady nominal charge. In order to feed current liquefaction processes with renewable hydrogen, a buffer system will become required. This thesis studies the effect of buffer and liquefaction combination on performances and cost. In order to carry out this liquefaction from intermittent source, the study is performed based on industrial data from a variable co-product hydrogen profile. This profile acts as a simplified case. The scope of the study is drawn by considering compressed hydrogen as temporary storage for the buffer while liquefaction unit is modelled around Linde Leuna cycle. The technical-economical study covers sensitivity analysis on both buffer and liquefaction unit. For the buffer unit, storage capacity, storage pressure, liquefaction flexibility and recuperation rate impacts are examined. Liquefaction sensitivity analysis includes pressure drop, electricity cost and capacity study. It is highlighted that 100% gaseous hydrogen recovery is not profitable due to high costs increase for recuperation higher than 95%. Storage pressure and capacity as well as liquefaction flexibility drive buffer cost and recuperation rate of the co-product hydrogen. Considering liquefaction study, results highlight that pressure drops cause first order deviations in energy consumption as well as on cost. Results show that the specific buffer cost is evaluated between 71% and 59% of liquefaction cost. Hence the thesis raises attention on future work on heat exchangers design, pressure drop optimization and liquefaction unit flexibility to allow an optimized renewable liquid hydrogen production.
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Chen, Guo Fu. "The diffusion of muonic hydrogen atoms in hydrogen gas." W&M ScholarWorks, 1990. https://scholarworks.wm.edu/etd/1539623790.
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This experiment measured the time distribution of muonic hydrogen atoms which were formed when negative muons were brought to rest in H{dollar}\sb2{dollar} gas, containing Au target foils, at five pressures (750 mbar, 375 mbar, 188 mbar, 94 mbar and 47 mbar at 4.6 mm foil spacing). A Monte Carlo method is applied for deducing the initial velocity distribution, and preliminary results are obtained. The initial velocity distribution of {dollar}\mu{dollar}H atoms is reasonably well described as a 'Maxwellian' velocity distribution with a mean energy E = 3.4 eV. The corresponding muon mean capture energy is obtained: E{dollar}\sb{lcub}\rm c{rcub}{dollar} {dollar}\approx{dollar} 34 eV for {dollar}\mu{dollar}H atom and E{dollar}\sb{lcub}\rm c{rcub}{dollar} {dollar}\approx{dollar} 68 eV for {dollar}\mu{dollar}H{dollar}\sb2{dollar} molecules. We also find the negative muon capture energy distribution is exponential.;In addition, a significant improvement of the negative muon mean life {dollar}\tau{dollar} in Au is abtained in this experiment.: {dollar}\tau\sb{lcub}\rm Au{rcub}{dollar} = 69.716 {dollar}\pm{dollar} 0.144 ns. The "full decay curve fitting method" which we use in this experiment has an advantage over the previous method in three aspects: (1) We have measured the mean life and determined the time resolution {dollar}\sigma{dollar}(E) of a detector at a particular energy level; (2) We have determined the effective zero time of the decay curve; (3) We have provided a possible way to measure the mean life {dollar}\tau{dollar} when {dollar}\tau{dollar} is less than the time resolution {dollar}\sigma{dollar}(E) of the detector ({dollar}\tau{dollar} {dollar}<{dollar} {dollar}\sigma{dollar}(E)).
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Qian, Yun. "Self-assembled Peptide Hydrogels for Therapeutic H2S Delivery." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/101094.
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Hydrogen sulfide (H2S) is a gasotransmitter that is produced endogenously and freely permeates cell membranes. It plays important roles in many physiological pathways, and by regulating these pathways, it provides many therapeutic effects. For example, H2S dilates vascular vessels, promotes angiogenesis, and protects cells from oxidative stress. Due to its therapeutic effects, H2S has been used as a potential treatment for diseases like diabetes, ischemia-reperfusion injuries, lung diseases, ulcers and edemas, among others. To apply H2S for therapeutic applications, two challenges need to be addressed. The first challenge is the H2S donor, which not only provides H2S but must be stable enough to avoid side effects caused by overdose; and the second challenge is the delivery strategies, which transport the H2S to the target sites.
A series of S-aroylthiooximes (SATOs), an H2S releasing compound, were synthesized and conjugated to peptide sequences to form H2S-releasing aromatic peptide amphiphile (APA) hydrogels. APAs formed nanofibers, which were stabilized by beta-sheets and aromatic stacking. The self-assembled structures were affected by the substituents on the aromatic rings of SATOs, leading to the formation of twisted nanofibers. After the addition of cysteine, H2S was released from the APAs with half-lives ranging from 13 min to 31 min. The electron-donating groups slowed down the H2S release rate, while the electron-withdrawing groups accelerated the release rate. Therefore, the release rates of H2S were controlled by electronic effects. When self-assembled structures were formed, the H2S release rate was slowed down even more, due to the difficulties in cysteine diffusion into the core of the structures.
Antimicrobial effects were also discovered using the H2S releasing APA hydrogels. The H2S-releasing dipeptides S-FE and S-YE formed self-assembled twisted nanoribbons and nanotubes, respectively. The non H2S-releasing control oxime dipeptides C-FE and C-YE were also synthesized. The C-FE formed nanoribbons while the C-YE only showed non-specific aggregates. S-FE and S-YE released H2S with peaking times of about 41 and 39 min. Both the self-assembled structures and the release rates were affected by their packing differences. In vitro and ex vivo experiments with Staphylococcus aureus (Xen29), a commonly found bacterium on burn wounds, showed significant antimicrobial effects. APAs S-FE and C-FE eliminated Xen29 and inhibited the biofilm formation, while S-FE always showed better effects than C-FE. These antimicrobial H2S-releasing APA hydrogels provide a new approach to treat burn wound infections, and provide healing benefits due to the therapeutic effects of H2S.<br>Doctor of Philosophy
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Riley, Duncan John. "First principles simulations of hydrogen-bonded and hydrogen storage systems." Thesis, University of Salford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490280.
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CORDARO, RICHARD BRIAN. "ELECTRON IMPACT DISSOCIATIVE IONIZATION OF HYDROGEN, WATER, AND HYDROGEN SULFIDE." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188028.
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The dissociative ionization by electron impact of H₂, H₂O, and H₂S was investigated between the electron impact energies of 20 and 45 eV. Protons were the detected fragments, and a time-of-flight method was used to measure the proton kinetic energies. By also measuring the thresholds for the production of discrete energy groups of protons, it was possible to determine the dissociation limits and kinetic energy distributions for individual electronic states. It was found that autoionizing states that lead to dissociation were the major contributors of proton fragments for all of the molecules investigated. Some of the measurements are tabulated in the following table. (UNFORMATTED TABLE FOLLOWS) Molecule Threshold Dissociation Probable Probable (eV) limit (eV) state fragments H₂ 24.5±1.0 18.0±1.0 Q₁ ¹Σ(g)⁺ H⁺, H(1S) 30.5±1.0 18.0±1.0 Q₁ ¹Πᵤ H⁺, H(1S) 36.5±1.0 -- ²Πᵤ H⁺, H(2P) H₂O 24.5±1.0 19.5±1.0 -- H⁺, OH (X²Π) 29.5±1.0 23.0±1.0 -- H⁺,O(³P),H(1S) H₂S 25.5±1.0 18.0±1.0 -- H⁺, HS (X²Π) 32.0±1.0 -- -- H⁺, . . . 42.0±1.0 -- -- H⁺, . . . (TABLE ENDS)
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Buan, Marthe Emelie Melandsø. "Photoelectrochemical Hydrogen Production." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19101.
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The possibilities for using CaNb2O6 as a photocatalyst in direct water splitting have been evaluated by investigating the electronic structure of the material. In addition the oxide was doped with nitrogen in order to modify the electronic structure and obtain visible light absorption. Experimental techniques such as electrochemical impedance spectroscopy (EIS), photocurrent, and diffuse reflectance spectroscopy (DRS) were combined with theoretical approaches to determine the bandgap, flatband potential and quasi-Fermi levels of the photocatalyst. CaNb2O6 was prepared by a sol-gel synthesis and doped with nitrogen by heat treatment of the oxide powder in an ammonia atmosphere. X-ray diffraction (XRD) confirmed phase pure orthorhombic CaNb2O6 for both pure and N-doped oxide and excluded a possible transformation of the oxide into an oxynitride. Upon illumination anodic photocurrents were observed implying that CaNb2O6 was an n-type semiconductor due to oxygen vacancies in the lattice. From the wavelength dependency of the photocurrent a direct bandgap of 3.7eV and an indirect bandgap of 3.4eV were determined for undoped CaNb2O6. Doping with nitrogen altered the optical properties of the oxide and shifted the absorption edge into the visible light region. Calculations using the density functional theory (DFT) attributed the change in absorption properties to the formation of narrow energy bands above the valence band of pure CaNb2O6. An alternative explanation could be a hybridization of N 2p and O 2p bands. Correspondingly a reduction of the bandgaps for N-doped CaNb2O6 with respect to the undoped oxide was identified. Impedance was applied to determine the flatband potential of CaNb2O6 from Mott-Schottky plots. However the obtained results seemed to be dominated by contributions from the electrode substrate. Theoretical investigations concluded that pinhole-free oxide layers creating an ohmic contact with the substrate are required in order to designate the observed impedance response to the space charge capacitance. Quasi-Fermi level measurements indicated a low photocatalytic activity of CaNb2O6 as no photocurrent could be detected. Further investigations are needed to identify the cause of the photocurrent limitations. Nevertheless probable explanations could be low conductivity in CaNb2O6, high concentrations of recombination centers or slow charge transfer kinetics. The latter was confirmed for porous oxide layers as the addition of a hole scavenger increased the measured photocurrent. Positive photocurrent transients were also observed for porous CaNb2O6 films and could be related to either the diffusion of electrons through the porous oxide layer or to a photoanodic decomposition of the photocatalyst.
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Hürlimann, Martin Dominik. "Cryogenic hydrogen maser." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/29116.
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A new type of atomic hydrogen maser that operates in a dilution refrigerator has been developed. In this device, the hydrogen atoms circulate back and forth between a microwave pumped state invertor in high field and the maser cavity in zero field.
A prototype maser with a small maser cavity has been built and the results obtained so far are encouraging. Stable maser oscillations were observed for temperatures of the maser bulb between 230 mK and 660 mK and for densities up to 3 x 1012cm⁻³. The short term frequency stability was measured with the help of two high quality quartz crystal oscillators by the three-cornered-hat method. The observed fractional frequency fluctuations for an averaging time of 1 s were 6.3 ± 3.7 x 10⁻¹⁴, which is lower than the results from the best room temperature masers. In conjunction with the stability measurements, the phase noise of the maser electronics was investigated. In particular, the temperature dependence of the phase noise of the cooled preamplifier was measured and it was shown that anomalous high noise levels between 2.2 K and 4.2 K are caused by the boiling of the liquid helium.
From the temperature dependence of the maser frequency, the binding energy E[sub B] of H on ⁴He could be determined to a high precision. The result is E[sub B] = 1.011 ± 0.010 K.
An extensive computer simulation program has been written that models the operation of the cryogenic hydrogen maser. It has been used to analyze and interpret some of the data. In addition, this simulation program is helpful for the design of an improved second generation cryogenic maser. Based on the present data and the model calculations, a new pumping scheme is proposed that is expected to increase the efficiency of the state invertor significantly.<br>Science, Faculty of<br>Physics and Astronomy, Department of<br>Graduate
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Almazroai, Layla S. "Photocatalytic hydrogen production." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54920/.
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Due to the environmental problems arising from the combustion of fossil fuels and their depletion, the production and use of renewable fuels have grown rapidly in recent years. Hydrogen is among the promising fuels of the future as the only material that can be produced from the burning of hydrogen in air is water. The production of hydrogen by the photocatalytic water splitting method involving a semiconductor is a promising development in the field of energy and the environment, and this technique was employed in this work. TiO<sub>2</sub> and palladium were the main photoactive support and loaded metal used in this project, respectively. The hydrogen production, whether from water/methanol solution or water alone, was investigated by illumination of the catalyst by UV irradiation produced from an Xe arc lamp. The reactions were performed in liquid or gas phase under an argon atmosphere as an inert gas. The gaseous products were collected and analysed using gas chromatography. The main method used in Pd loading was the impregnation method. 0.5% and 0.1% wt Pd loading were the best in terms of hydrogen production rate in liquid and gas phase reactions respectively. 0.5% Pd/TiO<sub>2</sub> (P25) was used in the remaining experiments to investigate some of the variables, to maximize the rate of H<sub>2</sub> production. Glycerol displayed an activity and produced hydrogen and carbon dioxide, as in the case of methanol but in much higher quantities. Loading of mesoporous TiO<sub>2</sub> by a different weight of Pd, which had a high surface area, gave less hydrogen than Pd/P25 whether in liquid or gas phase reactions. The efficiency of Pd loaded titania (P25, pure anatase or anatase prepared by CHFS) doped by non-metals such as nitrogen, silver or strontium was low and less than Pd/TiO<sub>2</sub>. Hydrogen produced over Pd/TiO<sub>2</sub>, Au/TiO<sub>2</sub> and TiO<sub>2</sub> from water photolysis was also very low. The recombination between hydrogen and oxygen (back reaction) was studied over these catalysts and it was found that it was fastest on Pd/TiO<sub>2</sub> whether in the dark or in the presence of light. For Au/TiO<sub>2</sub>, the light enhanced the hydrogen and oxygen reaction.
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Pearce, Steven Mitchell. "Hydrogen enhanced combustion." Thesis, University of Canterbury. Mechanical Engineering, 2000. http://hdl.handle.net/10092/6047.
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Current four stroke engine research objectives focus on increasing part load thermal efficiency while reducing exhaust emissions. Methods currently employed to achieve this are homogeneous charge lean burn technology, stratified charge lean burn technology and the use of alternative fuels. Of all possible alternative fuels hydrogen is viewed by many as being, ultimately, the fuel of the future. Methanol is regarded as being a likely transitional fuel between the current petroleum transport fuels and hydrogen. Hydrogen is known to be effective in extending the operating lean limit of an engine when used in small amounts in conjunction with conventional fuels.
This thesis presents the results of an investigation into the use of hydrogen as a supplementary fuel in a methanol fuelled Ricardo E6 engine. Three methods of introducing supplementary hydrogen into the engine were investigated: Untimed manifold injection, early direct injection and injection through a modified spark-plug.
Suitable injection systems were designed and tested on the Ricardo E6 engine. An engine management system, data acquisition system and post processing software were developed to enable data to be acquired and analyzed. The direct injection systems were the subject of schlieren visualization investigations of injected gas distribution to improve performance and elucidate engine related phenomena. Results detailing the effects of hydrogen supplementation on the engine performance, combustion and exhaust gas emissions are presented and discussed.
The early direct injection of hydrogen through a dedicated cylinder head tapping proved to be the least effective method of introducing supplementary hydrogen in the Ricardo E6 engine. The position of the injector diametrically opposite the spark-plug coupled with low levels of bulk mixture motion in the cylinder resulted in the formation of an inversely stratified charge (lean near spark-plug) even when injection commenced very early in the compression stroke. The inversely stratified charge resulted in a given level of hydrogen supplementation not being as effective as was the case in the other two fuelling systems.
The homogeneous air/fuel mixture formed by the untimed manifold injection of hydrogen was found to have a beneficial effect on both the combustion and emissions of the engine especially in lean air/fuel mixtures. Introducing supplementary hydrogen into the inlet manifold of the engine was however found to reduce the volumetric efficiency of the engine, reducing the level of output power produced by the engine.
Injecting hydrogen through a modified spark-plug was found to be the most effective way of introducing supplementary hydrogen. The improved performance of the modified spark-plug system over the other two systems was found to be due to the presence of a localized hydrogen/air mixture at the spark-plug electrodes at the time of ignition. Extension of the lean limit past that possible with methanol alone was demonstrated whilst maintaining both a high thermal efficiency and low indicated specific unburned hydrocarbon emissions.
Direct injection of supplementary hydrogen into the combustion chamber, either with the aim of forming a homogeneous charge, or forming a richer air/fuel mixture in the vicinity of the spark-plug without the use of a pre-chamber, has not been reported previously in the published literature. The investigation of both of these fuelling methods is presented in this thesis and constitutes an original contribution to the field of engine research.
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Chamberlain, Charles William. "Hydrogen-antihydrogen interactions." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395602.
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Dickinson, Amanda Jane. "Photocatalytic hydrogen production." Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360725.
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Prior, David V. "Hydrogen-bond basicity." Thesis, University of Surrey, 1988. http://epubs.surrey.ac.uk/847920/.
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A general scale of solute hydrogen-bond basicity has been constructed using a vast body of 1:1 hydrogen-bond equilibrium constants taken from literature. The data is assembled as a series (or set) of log K values for bases measured against a given hydrogen-bond acid in dilute tetrachloromethane solution. 34 such sets have been collected and a computational method regresses the log K data into 34 optimized equations of the form; log K[(set1)] = LA[i]. log K[H][B] + De[i] (1) For each set, the constants (LA and De) characterize the particular reference acid and the log K HB values characterize (and thereby scale) the bases over all sets. Certain acid-base combinations must, however, be excluded from equation 1 and this provides evidence that the log K HB scale is not entirely general towards all reference acids. In the regression procedure, use has been made of the novel observation that the lines represented by equation 1 intersect at a point where log K = log K HB = -1. 1. It is further shown that this condition enables the estimation of 1: 1 hydrogen-bond log K values in tetrachloromethane via equation 2; log K = 0.3421. (log K HA + 1. 1)(log HB + 1. 1) - 1.094 (2) where log K HA is a scale of solute hydrogen-bond acidity. The log K HB scale has been analysed in terms of the two principle factors of basicity according to the method devised by Maria and Gal et al. This analysis is shown to be informative in establishing and interpreting the relationships of log K HB with other basicity-dependent properties. For the most part, the experimental studies undertaken are concerned with a critical examination of the existing methods of determining G and H for 1:1 hydrogen-bond formation. The customary assumption of an exclusive 1:1 model of acid-base association in dilute solution has been tested with respect to the interaction of cyclohexanone with 3,5-dichlorophenol in cyclohexane. Using infrared spectroscopy, evidence for higher complex formation is presented and a method has been developed for determining simultaneously the formation constants of both the 1: 1 (AB) and 2: 1 (A2B) complexes (K1 and K2, respectively). 2:1 complex formation is also shown to interfere significantly with the K and H values obtained from a classical calorimetric titration procedure, limiting its application to hydrogen-bonding studies. For this reason, an improved calorimetric method for the independent determination of 1:1 hydrogen-bond enthalpies has been developed. Application of the devised methods to the interaction of 3,5-dichlorophenol with series of aliphatic ketones and aliphatic ethers in cyclohexane has yielded the values of K1 and K2, together with the thermodynamic parameters (G1, H1 and S1) of 1:1 hydrogen-bond formation. Within each series, the small differences in K1 and H1 resulting from the very subtle structural variations in the base component are discussed in terms of electronic and steric effects. The values of K1 and K2 are found to be consistent with a theoretically derived equation predicting a linear relationship between log K1 and log K2, and the values of H1 are used to critically appraise the validity of the Badger-Bauer relationship.
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Zhang, Lingzhi. "Catalytic Hydrogen Production." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1218493937.
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Corkhill, P. H. "Novel hydrogel polymers." Thesis, Aston University, 1988. http://publications.aston.ac.uk/9725/.
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Hydrogels may be conveniently described as hydrophilic polymers that are swollen by, but do not dissolve in water. In this work a series of copolymer hydrogels and semi-interpenetrating polymer networks based on the monomers 2-hydroxyethyl methacrylate, N-vinyl pyrrolidone and N'N' dimethyl acrylamide, together with some less hydrophilic hydroxyalkyl acrylates and methacrylates have been synthesised. Variations in structure and composition have been correlated both with the total equilibrium water content of the resultant hydrogel and with the more detailed water binding behaviour, as revealed by differential scanning calorimetry studies. The water binding characteristics of the hydrogels were found to be primarily a function of the water structuring groups present in gel. The water binding abilities of these groups were, however, modified by steric effects. The mechanical properties of the hydrogels were also investigated. These were found to be dependent on both the polymer composition and the amount and nature of the water present in the gels. In biological systems, composite formation provides a means of producing strong, high water content materials. As an analogy with these systems hydrogel composites were prepared. In an initial study of these materials the water binding and mechanical properties of semi-interpenetrating polymer networks of N'N'dimethyl acrylamide with cellulosic type materials, with polyurethanes and with ester containing polymers were examined. A preliminary investigation of surface properties of both the copolymers and semi-interpenetrating polymer networks has been completed, using both contact angle measurements and anchorage dependent fibroblast cells. Measurable differences in surface properties attributable to structural variations in the polymers were detected by droplet techniques in the dehydrated state. However, in the hydrated state these differences were masked by the water in the gels. The use of cells enabled the underlying differences to be probed and the nature of the water structuring group was again found to be the dominant factor.
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Ma, James J. "Novel hydrogel polymers." Thesis, Aston University, 1995. http://publications.aston.ac.uk/9661/.
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Hydrogels are a unique class of polymers which swell, but do not dissolve in water. A range of 2-hydroxyethyl methacrylate based copolymer hydrogels have been synthesised and are described in this thesis. Initially, hydrogels were synthesised containing acryloylmorpholine, N,N-dimethyl acrylamide and N-vinyl pyrrolidone. Variations in structure and composition have been correlated with the sequence distribution, equilibrium water content (EWC) , mechanical and surface properties of the hydrogels. The sequence distribution was found to be dependant on the structure and reactivity of the monomers. The Ewe was found to be dependant on the water structuring groups present in the hydrogel, although the water binding abili ties were modified by steric effects. The mechanical properties were also investigated and were found to be dependant on the monomer structure, sequence distribution and the amount and nature of water in the hydrogel. The macroscopic surface properties of the hydrogels were probed using surface energy determinations and were found to be a function of the water content and the hydrogel composition. At a molecular level, surface properties were investigated using an in vitro ocular spoilation model and single protein adhesion studies. The results indicate that the sequence distribution and the polarity of the surface affect the adhesion of biological species. Finally, a range of 2-hydroxyethyl methacrylate based copolymer hydrogels containing both charged monomer groups and linear polyethers have been synthesised and described. Although variations in the Ewe are observed with the structure of the monomers, it was observed that the Ewe increased due to the polar character of the charged monomers and the chain length and hydrophilicity of the polyethers. Investigation of these hydrogel surfaces revealed subtle changes. The molecular surface properties indicate the significance of the effect of charge and molecular mobility of the groups expressed at the hydrogel surface
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Schneider, Robin. "About Supersymmetric Hydrogen." Thesis, Uppsala universitet, Teoretisk fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-329298.
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Jana, Prabhas. "Environ-friendly production of hydrogen peroxide from direct catalytic liquid phase oxidation of hydrogen or hydrogen-containing compounds." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2007. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2571.
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Chen, Hong. "Development of multi-functional polymeric biomaterials." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1490706379312092.
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Bibi, Nurguse. "Elastase responsive hydrogel dressing for chronic wounds." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/elastase-responsive-hydrogel-dressing-for-chronic-wounds(f2a1f950-d38d-4cb2-8b8e-3c1e10ef7910).html.
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Chronic wounds are a major financial and clinical burden causing the deaths of millions per year. Over expression of elastase is well documented as the main culprit that delays the normal wound repair process within chronic wounds. The aim of this thesis is to design a responsive chronic wound dressing based on the hydrogel polymer, PEGA (polyethylene glycol acrylamide) in the form of particles to mop-up excess elastase by exploiting polymer collapse in response to elastase hydrolytic activity within sample fluids mimicking the environment of chronic wounds. PEGA particles were functionalised with enzyme cleavable peptides (ECPs) containing charged residues. Upon cleavage the charge balance changes, causing polymer swelling and consequent elastase entrapment. The pH range of chronic wounds is reported in the range of 5.45 - 8.65. Due to its pI which is around 8.3, within this range elastase exist both in its cationic and anionic forms. To accommodate a hydrogel dressing that could selectively entrap excess elastase both in its cationic and anionic, oppositely charged ECPs were designed. In its cationic form, elastase was found to have a high preference of cleaving ECPs and penetrating into PEGA particles bearing negative charges. In contrast, in its anionic form the opposite effect was observed, wherein elastase preferred to cleave ECPs and penetrate PEGA particles bearing positive charges. The diffusion, accessibility and entrapment of elastase into functionalised PEGA particles was explored using various fluorescence microscopy techniques. Removal of the charged residue by elastase showed a reduction in particle swelling causing the pores of PEGA particles to become restricted. In this manner, cleaved PEGA particles prevented the accessibility of molecules with a molecular weight as low as 20 kDa into the cleaved PEGA particles. Since elastase has a molecular weight of 25.9 kDa the collapsing of the pores within PEGA particles entrapped elastase inside the interior of cleaved PEGA particles. In its cationic form (at pH 7.4) elastase was found to penetrate and become trapped more into both negative and positive PEGA particles compared to neutral particles. The negative particles were shown to trapped cationic elastase within 2 minutes compared to the positive particles. In contrast, the neutral particles failed to retain and encapsulate elastase as the fluorescence inside the neutral particles was found to decrease. Coinciding with these observations, after sample fluids containing elastase were treated with functionalised PEGA particles, the residual elastase activity in sample fluids was reduced more by the charged PEGA particles compared to neutral particles. The cell culture studies demonstrated that the elastase activity observed in human dermal fibroblasts (HDF) was also reduced more by the charged particles compared to the neutral particles. However, the positive particles were found to significantly reduced HDF-elastase activity compared to both the negative and neutral PEGA particles. Overall, this thesis exemplifies that on the basis of charge selective cleaving of ECPs coupled to PEGA particles can be exploited to selectively remove excess proteases such as elastase from sample fluids mimicking the environment of chronic wounds.
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Pacella, Francesca. "Tuning the crosslinking chemistry for self-healable mucin hydrogel synthesis and application." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-279301.
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Immune-orchestrating biomaterials that precisely modulate the immune reac-tion to the host could lead the way for improving the implantation outcomein the transplantation field, in comparison to passive biomaterials. The lab-oratory of Dr. Thomas Crouzier has shown hydrogels derived from mucinsare capable of orchestrating the immune response mediated by foreign bodyresponse (FBR), as a result of evading fibrosis. Further, a recent study fromhis group showed sialic acid on mucin hydrogels is essential for the immuno-logical activity of those materials. Mucin glycans transiently activated thendampened macrophages, important orchestrators for material-mediated FBR,in a sialic acid-dependent manner for the majority of cytokines followed. Thematerial properties such as rheological properties, self-healing capacity, andstability, can be governed by the crosslinking chemistry used and have a drasticimpact on the functionalities of the materials. In this project, various cross-linking strategies are applied to tune the hydrogel properties. We show thatthe robust cross-linking formed mucin hydrogels having a 1.5% (wt/v) bettersupported insulin-secreting cells form islet-like organoids, compared to 2.5%mucin hydrogels. We then investigate the self-healing properties of the newmucin hydrogels and their interactions with various cell systems.<br>Immunologiska biomaterial som specifikt modulerar en immunologisk reak-tion hos värden kan vara vägen till att förbättra resultatet av en transplantationi jämförelse med att använda passiva biomaterial. Inom laboratoriet lett av Dr.Thomas Crouzier har det kunnat påvisas att hydrogels erhållna från mucinerär kapabla till att förändra en immunlogisk respons, Foreign Body Respon-se (FBR) vilket resulterat i att kringgå fibrosis. Utöver detta har ytterligareen studie utförts av hans grupp vilken kunde påvisa att sialinsyra på mucinhydrogel är essentiellt för den immunologiska aktiviteten för dessa biomateri-al. Mucin glykaner aktiveras tillfälligt för att dämpa bildandet av makrofager,vilket är viktigt vid biomaterial FBR i ett sialinsyra-beroende för bildandet avmajoriteten av cytokiner. Materialegenskaperna såsom reologiska egenskaper,självläkande kapacitet, och stabilitet kan regleras genom en krosslänkad kemisom har en drastisk impakt för funktionen för biomaterialen. I detta projekt, ärflera krosslänkande strategier tillämpade för att förstå egenskaperna för hyd-rogelerna. Vi har kunnat påvisa att robusta krosslänkande system av mucinhydrogel bestående av 1.5% (wt/v) ger bättre support till insulin sekreterandeceller att bilda islet liknande organider, att jämföra med 2.5% mucin hydrogel.Vi undersöker sedan den självläkande egenskaperna av nya mucin hydrogeleroch deras interaktioner med ett flertal olika cellsystem.
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Sapárová, Alica. "Příprava a vlastnosti agarosového hydrogelu s micelárními doménami." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2017. http://www.nusl.cz/ntk/nusl-316182.
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This diploma thesis was focused on the system of agarose hydrogels with micellar domains. Polysaccharide agarose was used for the preparation of hydrogel matrices. Septonex was chosen as a surfactant. The release of solubilizate from the agarose hydrogel matrix was studied with a hydrophobic dye Sudan III in order to obtain a model system of hydrophobic solubilized drugs. Sudan III was solubilized via surfactant´s micels. Subsequently, this micellar aqueous solution with the dissolved dye was used to prepare the agarose hydrogel. The system was prepared in the environment of deionized water and physiologic solution. The gradual release of the dye into deionized water and physiologic solution was studied for 22 days using the UV-VIS spectrophotometry method. It was found that after 14 days the concentration of the releasing dyes into the deionized water was decreased. The cause is that after 14 and 22 days there was a slight degradation of gels, which was detected using the rheology method. Using the rheology method it was also found that Septonex does not affect the gel formation process.
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Chollet, Benjamin. "Hydrogels greffés stimulables comme actionneurs microfluidiques." Electronic Thesis or Diss., Paris 6, 2015. http://www.theses.fr/2015PA066494.
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Nous développons une nouvelle approche des actuateurs microfluidiques à base d’hydrogels stimulables. Contrairement aux approches précédentes, les hydrogels sont synthétisés et greffés à la paroi inférieure du microcanal avant la fermeture du système. Nous utilisons une nouvelle stratégie de synthèse pour les films d’hydrogels stimulables par chimie click thiol-ène. Les films sont obtenus par dépôt, sur des surfaces fonctionnalisées avec des thiols, d’un mélange de chaînes polymères préformées et d’un réticulant dithiol. Le greffage et la réticulation s’obtiennent simultanément par une activation thermique ou par irradiation UV. Des films et des micro-motifs sont obtenus sur une large gamme d’épaisseur allant de la centaine de nanomètres à plusieurs microns. Nous intégrons les motifs d’hydrogels stimulables dans les microcanaux pour réaliser des actionneurs. Nous étudions des actionneurs thermosensibles réalisés avec des hydrogels de poly(N-isopropylacrylamide). Avec la température, les motifs d’hydrogels gonflent ou dégonflent en absorbant/expulsant l’eau de manière réversible. L’effet est rapide (inférieur à la seconde), la transition abrupte (quelques degrés autour de la LCST à 32°C) et l’amplitude de déformation est importante (gonflement de 400%). Les micro-vannes réalisées avec cette nouvelle approche présentent de très bonnes performances et une grande durabilité. Nous avons aussi réalisé de nouveaux actionneurs reconfigurables fonctionnant comme des pièges microfluidiques. Ces actionneurs microfluidiques innovants offrent de nombreuses perspectives de par la facilité de leur mise en œuvre, leurs performances et l’intégration sur des micro-puces à haute densité<br>We develop a new method to build microactuators using stimuli-responsive hydrogels. The hydrogel is synthesized with covalent attachment to the microchannel bottom walls prior to closing the microsystem, contrarily to previous approaches. We use a new stimuli-responsive hydrogel films synthesis pathway. This synthesis is based on thiol-ene click chemistry. The formation of films is achieved by adding bifunctional thiol molecules as cross-linkers to ene-functionalized preformed polymers on thiol-modified surfaces. The cross-linking and grafting are simultaneously performed either by thermal activation or UV-irradiation. Hydrogel films and micro-patterns are easily obtained in a wide range of thickness from hundred nanometers to several microns. We show that these responsive hydrogels patterns can be integrated into microfluidics channels to build microactuators. We focus on thermo-sensitive actuators made from poly(N-isopropylacrylamide). Under temperature, hydrogel patterns reversibly swell and collapse by absorbing/expulsing water. The phase transition is rapid (lower than 1 second), abrupt (a few degrees around the LCST at 32°C) and the deformation amplitude is high (400% swelling). Microvalves obtained by this approach exhibit high performances and durability. Moreover, we develop new reconfigurable actuators functioning as microfluidic traps. These new-concept microfluidic actuators offer wide possibilities because of their ease of fabrication, their performances and their ability to be integrated into high density
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Mostajeran, Mehdi. "Catalyzed Hydrogen Release from BH- and BNH-based Hydrogen Storage Materials." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36875.
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In order to reduce our ties to fossil-based energy and mitigate the undeniable impacts of climate change on the environment, remarkable efforts have been directed over the last 4 decades toward developing renewable energy sources such as solar, wind, geothermal, etc. For transportation applications biofuels, electricity and hydrogen all offer potential solutions although current usage is still largely linked to fossil fuels (bio-based ethanol-gasoline mixtures, power generation for battery recharging, and steam reforming for hydrogen production). While hydrogen offers the greatest potential in terms of energy density, its poor volumetric density (0.01 MJ/L at RT) requires costly compression and pressurized storage. When future technology finally allows for efficient hydrogen release from water splitting, we need to have optimal solutions in place for hydrogen storage. One promising solution is chemical hydrogen storage in which thermolysis of a chemical precursor affords a controlled hydrogen release that can then be reversed in an off-board regeneration step. With a focus on maximum gravimetric hydrogen storage, various BNH compounds have been shown to be promising chemical hydrogen storage precursors. In this Thesis we summarize the state of the art in B-N-H hydrogen storage compounds (Chapter 1) and then investigate several new chemical hydrogen storage solutions with a focus on portable power generation.
In the first project (Chapter 2) we sought to prepare a robust, base-metal borohydride hydrolysis catalyst for use in a custom hydrogen generator designed to use the reaction heat to help separate the borate spent fuel. Active ‘reverse opal’ layered double hydroxide (LDH) catalysts were prepared and tested. While the classical Ni-Mg-Al LDH released 3.4 equiv. of hydrogen at 50 °C in 150 minutes, the polystyrene templated Ni-Mg-Al catalyst released 4 equiv. of hydrogen with a higher initial rate under the same reaction conditions. The long-term objective of this project was to test these catalysts in fuel cells for underground mine forklifts with our industry collaborator (Kingston Process Metallurgy Inc.).
In the next three chapters, the synthesis and hydrogen release properties of ammine metal borohydrides [M(BH4)m(NH3)n, AMBs] were investigated. As promising hydrogen storage materials with high hydrogen content (10-15 wt%), AMBs can access lower hydrogen release temperatures resulting from the combination of protic (N-Hδ+) and hydridic (B-Hδ-) hydrogens. While AMBs also do not suffer from diborane formation that plagues thermolysis of metal borohydrides, hydrogen release is often accompanied by small concentrations of ammonia that deactivate the fuel cell catalyst. Our objective for this work was to identify base metal catalysts that could suppress ammonia formation by further reducing the energy barrier to H2 release.
In Chapter 3 our studies of the solution synthesis of AMB materials (Y, La, Zn, etc.) in coordinating solvents such as tetrahydrofuran (thf) and diethyl ether revealed the unexpected formation of ammonia-borane (H3NBH3, AB). It was shown that while the amounts of produced AB correlate with the Zhang electronegativity for the s- and p-block metals, ionic radius is a stronger determining factor for the transition metals. It was also observed that reducible metals such as Ti and V produce large amounts of AB while Zn produced the least. This knowledge was then used in Chapter 4 to prepare pure samples of the Y and La complexes, M(BH4)3(NH3)4 that were characterized by thermal analysis (TGA-MS), powder X-ray diffraction, FT-IR and 11B and 1H MAS NMR spectroscopy. Furthermore, a series of base-metal nanoparticle catalysts, prepared using a novel route from MCl2 and liquid hexylamine-borane, was shown to suppress ammonia formation from these Y and La AMBs. Immobilizing 5 wt.% of Co NPs on Y(BH4)3(NH3)4 and 5 wt.% of Fe NPs on La(BH4)3(NH3)4 resulted in reduction of ammonia release by three- and fourfold, respectively. In Chapter 5 the attempted solution synthesis of Zn(BH4)2(NH3)2 revealed complications due to preferred formation of MIZn(BH4)3 [instead of Zn(BH4)2] from the reaction of ZnCl2 and MIBH4 (MI= Li, Na, K). As a result, the mixed-metal AMB, KZn(BH4)3(NH3)n was prepared and characterized. Although the effects of both heterogeneous and homogeneous catalysts were not as pronounced as those for Y and La, using 5 wt.% FeNPs resulted in fourfold reduction in the amount of released ammonia which led to a purer hydrogen stream (98.9 mol%) compared to the uncatalyzed thermolysis (97.0 mol%).
Finally, in Chapter 6 our results are considered vs. the current state of the art and suggestions are made for further investigations.
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Dowson, A. L. "Some aspects of hydrogen absorption and hydrogen embrittlement in alpha titanium." Thesis, University of Newcastle Upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382542.
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Ferrari, Federica. "Data analytics for hydrogen safety: prediction of Liquid hydrogen release characteristics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.
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Hydrogen can be adopted as a clean alternative to hydrocarbons fuels in the marine sector. Liquid hydrogen (LH2) is an efficient solution to transport and store large amounts of hydrogen, thus it is suitable for the maritime field. Additional safety knowledge is required since this is a new application and emerging risk might arise. Recently, a series of LH2 large-scale release tests was carried out in an outdoor facility as well as in a closed room to simulate spills during a bunkering operation and inside the ship’s tank connection space, respectively. The extremely low boiling point of hydrogen (-253°C) can cause condensation or even solidification of air components, thus enrich with oxygen the flammable mixture. This can represent a safety concern in case of ignition of the flammable mixture of LH2 and solid oxygen, since it was demonstrated that the resulting fire may transition to detonation. In this study, the abovementioned LH2 release experiments were analysed by using an advanced machine learning approach. The aim of this study was to provide critical insights on the oxygen condensation and solidification during an LH2 accidental spill and to evaluate whether the hydrogen concentration within the gas cloud formed due to the LH2 evaporation would reach the lower flammability limit. In particular, a model was developed to predict the possibility and the location of the oxygen phase change and of the hydrogen concentration above the lower flammability limit depending on the operative conditions during the bunkering operation (e.g. LH2 flow rate). The model demonstrated accurate and reliable predicting capabilities. The outcomes of the model can be exploited to select effective safety barriers and adopt the most appropriate safety measures in case of liquid hydrogen leakage.
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BARLOCCO, ILARIA. "HYDROGEN PRODUCTION FROM CHEMICAL HYDROGEN STORAGE MATERIALS USING CARBON-BASED CATALYSTS." Doctoral thesis, Università degli Studi di Milano, 2022. http://hdl.handle.net/2434/901855.
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The aim of this thesis is to design new catalytic systems in order to improve the performances of the existing catalysts to convert formic acid (FA) and hydrazine (N2H4 · H2O) into ultra-pure hydrogen in order to be effective in the future hydrogen economy. Different are the issues to solve in order to efficiently employ these chemicals in our energy transition. In particular, efficient carbon-based heterogeneous systems can effectively make enormous difference in the production of hydrogen from liquid carriers. Indeed, metal-based catalysts and especially Pd-based ones offer enhanced activity also at room temperature, but selectivity and stability need to be improved to be industrially applicable. In addition, carbon materials have the advantage of being easily tuned through variation in their structure, for example, changing the surface area and porosity and adding functional groups or generating topological defects. Moreover, their stability in liquid phase reactions makes them auspicious candidates in catalytic processes.
For these reasons, the first part of this thesis is dedicated to the design of new catalytic materials with the aim to improve the catalytic behaviour compared to existing Pd-based catalysts for the selective decomposition of FA at mild reaction conditions. In particular, the effect of the metal-support interaction and the geometrical and electronic effect in alloyed catalysts play a fundamental role to enhance the catalytic performance (Chapter 3-5).
Chapter 3 is devoted to study the metal-support interaction by doping with O and P functionalities the carbonaceous support. In order to establish the presence of functional groups in the support and their effect on Pd nanoparticles, the obtained samples were then, characterised by Transmission Electron Microscopy (HR-TEM, STEM-HAADF and STEM-EDS) and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) simulations provided further insights in the interaction of Pd15 cluster with different support surfaces, i.e. pristine graphene (PG), carboxyl doped graphene (G_COOH), hydroxyl doped graphene (G_OH), carbonyl doped graphene (G_CO) and phosphate doped graphene (G_PO3H).
The effect of the addition of a second metal to Pd is considered (Rh in Chapter 4 and Au in Chapter 5). In particular, in Chapter 4 the synthesis of PdRh nanoparticles with different Pd:Rh molar ratios was studied. The obtained catalysts were characterised by Transmission Electron Microscopy (TEM) and Inductively coupled plasma optical emission spectroscopy (ICP-OES). For bimetallic catalysts, EDX-STEM analysis of individual nanoparticles was employed to investigate the presence of random-alloyed nanoparticles. Finally, PdRh catalysts were tested in the liquid-phase hydrogenation of muconic acid using formic acid as hydrogen donor.
Chapter 5 combines DFT and experimental data to disclose the role of gold in enhancing activity, selectivity and stability of palladium catalyst during the formic acid decomposition. PdAu bimetallic nanoparticles with different Pd:Au molar ratio were synthesised and the obtained catalysts were characterised by using Transmission Electron Microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP - OES). Finally, Density functional theory (DFT) calculations on Pd15, Au15 and Pd9Au6 clusters supported on a carbon sheet were then simulated to provide atomic level understanding to the beneficial effect of gold observed in the experimental results.
In addition, in order to decrease the cost and increase the environmental benignity of the catalyst, the application of metal-free carbon materials in the formic acid dehydrogenation is investigated (Chapter 6). Indeed, Commercial graphite (GP), graphite oxide (GO), and two carbon nanofibers (CNF-PR24-PS and CNF-PR24-LHT) were used as catalysts for the metal-free dehydrogenation reaction of formic acid (FA) in liquid phase. Raman and XPS spectroscopies were employed to characterize the materials and Density Functional Theory (DFT) calculations were utilized to study the role of defects in this reaction.
In the final results chapter (Chapter 7), the above reported metal-free carbocatalysts are employed for the hydrazine hydrate dehydrogenation reaction, in order to produce H2 without the presence of CO2. A combination of DFT and experimental studies were used to unravelling the hydrazine hydrate decomposition reaction on metal-free catalysts. The study focuses on commercial graphite and two different carbon nanofibers, Pyrolytically Stripped (CNF-PS) and High Heat-Treated (CNF-HHT), respectively treated at 700 and 3000 °C to increase their intrinsic defects.
Finally, Chapter 8 presents a summary of the main findings of this work and different possibilities to continue this research study.
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Kaur, Kuljeet. "Synthesis, evaluation, and applications of hydrogen sulfide-releasing supramolecular materials." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/104204.
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H2S is a biologically relevant signaling gas that is endogenously produced throughout the body. The (patho)physiological roles of H2S have led researchers to develop various compounds that decompose to release H2S (H2S donors) for exogenous H2S administration. However, many small molecule H2S donors suffer from poor solubility, low stability, and lack of control over H2S release rates. As a result, there has been an increasing interest in utilizing supramolecular materials for exogenous H2S delivery.
With growing potential applications of supramolecular H2S-releasing materials, it is important to explore their properties, e.g., solubility and stability under physiological conditions. We investigated the hydrolytic stability over a range of pH conditions of a series of peptides containing H2S-releasing S-aroylthiooximes (SATOs). The SATO-peptides showed structure–reactivity relationships with SATO ring substituents playing a crucial role in hydrolysis rates. Electron-donating substituents accelerate the rate of hydrolysis while electron-withdrawing substituents slows it down. We also explored their hydrolysis mechanisms at different pH values.
SATO-peptides were then used to form hydrogels at 1 wt.% triggered by Ca2+. Hydrogels can be applied directly at a site of interest, potentially improving the efficacy of H2S compared with small molecule donors that diffuse away. We developed a H2S-releasing hydrogel capable of slowly releasing H2S locally to test its efficacy on intimal hyperplasia. The hydrogel delivered H2S over the period of several hours and inhibited the proliferation of human vascular smooth muscle cells (VSMCs) significantly better than fast-releasing NaSH salts. This study shows a promising application of supramolecular H2S-releasing materials over widely used sulfide salts.
The macroscopic properties of peptide hydrogels could be further modulated to achieve additional control over the H2S release properties. We synthesized a series of peptide hydrogels incorporating different linker segments to study their effects on hydrogelation properties. Most peptides formed hydrogels but with significantly different rheological behavior. We found that peptides with flexible linkers such as ethyl, substituted O-methylene, and others, formed stronger hydrogels compared to those with more rigid linkers. Interestingly, we found that stiffer hydrogels released H2S over longer periods than softer ones by retarding the diffusion of a thiol trigger, likely due to bulk degradation of the soft gels but surface erosion of the stiff gels as they release H2S.<br>Doctor of Philosophy<br>H2S has long been known as a foul smelling gas until it was discovered that it is endogenously produced throughout the body and plays many (patho)physiological roles. Therapeutic benefits of H2S have led researchers to develop various compounds that release H2S (H2S donors) for exogenous H2S administration. However, many small molecule H2S donors suffer from poor solubility, low stability, and unregulated H2S release. As a result, there has been an increasing interest in utilizing materials for exogenous H2S delivery.
With growing potential applications of H2S-releasing materials, it is important to explore their properties, e.g., solubility and stability under physiological conditions. We investigated the stability of a series of peptides containing H2S-releasing S-aroylthiooximes (SATOs) over a range of pH conditions. The stability of SATO-peptides was dependent on chemical makeup of the SATO part of the peptides. We also explored their hydrolysis mechanisms at different pH values.
SATO-peptides were then used to form hydrogels triggered by Ca2+. Hydrogels can be applied directly at a site of interest, potentially improving the efficacy of H2S compared with small molecule donors that diffuse away. We developed a H2S-releasing hydrogel capable of slowly releasing H2S locally to test its efficacy on intimal hyperplasia. The hydrogel delivered H2S over the period of several hours and inhibited the proliferation of human vascular smooth muscle cells (VSMCs) significantly better than fast-releasing NaSH salts. This study shows a promising application of supramolecular H2S-releasing materials over widely used sulfide salts.
The macroscopic properties of peptide hydrogels could be further modulated to achieve additional control over the H2S release properties. We synthesized a series of peptide hydrogels incorporating different linker segments to study their effects on hydrogelation properties. Most peptides formed weak to strong hydrogels with calcium chloride.We found that peptides with flexible linkers formed stronger hydrogels compared to those with more rigid linkers. Interestingly, we found that stiffer hydrogels released H2S over longer periods than softer ones.