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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Crystal engineering with coordination, hydrogen- and halogen-bonds, and the construction of porous solids

Gunawardana, Chamara Abeywickramasinghe January 1900 (has links)
Doctor of Philosophy / Department of Chemistry / Christer B. Aakeröy / A set of multifunctional molecules [isomeric forms of 1-(pyridylmethyl)-2,2'-biimidazole] was synthesized and subjected to systematic co-crystallizations with selected hydrogen- and halogen-bond donors in order to explore the impact of interaction type, geometry and electrostatics on the resulting supramolecular architectures. The structural outcome with hydrogen-bond donors (carboxylic acids) is somewhat unpredictable because of the presence of the acid···biimidazole heterosynthon that can compete with biimidazole···biimidazole homosynthon. In contrast, the solid-state supramolecular behavior of those probe molecules is largely unchanged in halogen-bonded co-crystals. Only two types of primary interactions, the two-point hydrogen bonds responsible for pairing biimidazole moieties, and the single-point halogen bonds responsible for the co-crystal formation and structure extension, are present in these systems. The results highlight that, by incorporating geometric biases along with orthogonal interactions, one can effectively prevent synthon crossover which is of paramount importance in complex crystal engineering endeavors. Heterobifunctional ligands pave the way for elaborate metallo-supramolecular systems, and are also useful for combining metal-ligand bonding with other types of non-covalent interactions. Nine new acetylacetonate ligands featuring either pyridyl- or thiophenyl-heterocycles were successfully prepared, and their metal binding abilities were studied with selected di- and tri-valent transition metal ions. As expected, the acetylacetonate ligation to metal dications remains consistent. In each case, the metal is four-coordinate and resides in a square planar environment. Differences in the overall architectures arise from the role played by the terminal heterocycles and the solvent. In seven (out of nine) structures, the heterocyclic end is involved in a structure-directing interaction and it is more prevalent in ligands bearing 4-pyridinyl unit. Divergent molecules containing bulky substituents tend to produce porous materials via frustrated packing. Two rigid tetrahedral cores, tetraphenylmethane and 1,3,5,7-tetraphenyladamantane, grafted peripherally with four (trimethylsilyl)ethynyl moieties were found to have only isolated voids in their crystal structures. Hence, they were modified into tecton-like entities, tetrakis(4-(iodoethynyl)phenyl)methane [I₄TEPM] and 1,3,5,7-tetrakis(4-(iodoethynyl)phenyl)adamantane [I₄TEPA], and the effect of motif-forming characteristics of iodoethynyl units on molecular arrangement and crystal porosity was analyzed. I₄TEPM not only holds increased free volume compared to its precursor, but also forms one-dimensional channels. Furthermore, it readily co-crystallizes with Lewis basic solvents to afford two-component porous materials even though they suffer from stability issues. As the binding sites in I₄TEPM and I₄TEPA are tetrahedrally-predisposed, they can be further utilized for the modular assembly of highly symmetric, three-dimensional extended architectures. With that in mind, these two building blocks were subsequently allowed to react with various halide salts, and it was found that the reactions between I₄TEPM and tetraphenylphosphonium halides readily yield four-fold interpenetrated diamondoid networks sustained by C–I⋯X⁻ (X⁻ = chloride, bromide, iodide) halogen-bonding interactions. The halide anions exhibit mutual-induced fitting of their coordination and act as four-connecting tetrahedral nodes, while the tetraphenylphosphonium cations render essential templating information and structural support.
22

Multi-Scale Modeling of Mechanical Properties of Single Wall Carbon Nanotube (SWCNT) Networks

Gupta, Ankit 01 August 2017 (has links)
Single wall carbon nanotubes (SWCNTs) show a variety of unparalleled properties such as high electrical and thermal conductivity, high specific surface area (SSA) and a large stiffness under axial loads. One of the major challenges in tapping the vast potential of SWCNTs is to fabricate nanotube based macrostructures that retain the unique properties of nanotubes. Pristine SWCNT aerogels are highly porous, isotropic structures of nanotubes mediated via van der Waals (VDW) interactions at junctions. The mechanical behavior of such aerogels is examined in several experimental studies. However, it is necessary to supplement these studies with insights from simulations in order to develop a fundamental understanding of deformation behavior of SWCNT aerogels. In this study, the mechanical behavior of SWCNT networks is studied using a multi-scale modeling approach. The mechanics of an individual nanotube and interactions between few nanotubes are modeled using molecular dynamics (MD) simulations. The results from atomistic simulations are used to inform meso-scale and continuum scale finite element (FE) models. The deformation mechanism of pristine SWCNT networks under large compressive strain is deduced from insights offered by meso-scale simulations. It is found that the elasticity of such networks is governed by the bending deformation of nanotubes while the plastic deformation is governed by the VDW interactions between nanotubes. The stress response of the material in the elastic regime is dictated by the VDW stresses on nanotubes while in the plastic regime, both the VDW and axial deformation stresses on nanotubes drive the overall stress response. In this study, the elastic behavior of a random SWCNT network with any set of junction stiffness and network density is also investigated using FE simulations. It is found that the elastic deformation of such networks can be governed either by the deformation of the nanotubes (bending, axial compression) or deformation of the junctions. The junction stiffness and the network density determine the network deformation mode. The results of the FE study are also applicable to any stiff fiber network.
23

Application de l’analyse du cycle de vie lors de la conception de matériaux poreux à partir de la biomasse / Life cycle assessment approach for the eco-design of bio-based porous materials

Foulet, Amandine 09 October 2015 (has links)
La liqueur noire est produite en grande quantité dans les papeteries, en co-produit de la pâte à papier. Issue de la transformation du bois, elle représente une source importante de biopolymères non concurrentielle à l’industrie alimentaire. Par dispersion d’une phase organique dans la liqueur noire, des émulsions concentrées et stables ont été obtenues. Parmi les phases dispersées envisagées, l’huile de ricin et le 1,2-dichloroéthane ont été les plus adaptées. Par polymérisation de ces émulsions concentrées, la liqueur noire a permis d’obtenir des matériaux poreux appelés polyECs. L’analyse du cycle de vie a été appliquée tout au long de la préparation des polyECs et a montré que l’utilisation du 1,2-dichloroéthane, en tant que phase dispersée, serait moins néfaste pour l’environnement que l’utilisation de l’huile de ricin. Après pyrolyse, la matrice polymère des polyECs est devenue carbonée pour donner des carbones poreux, les carboECs. Grâce à leur structure microporeuse et mésoporeuse, ces carboECs biosourcés présentent un intérêt pour le stockage d’énergie, notamment les supercondensateurs. Des essais préliminaires ont montré que les performances électrochimiques des carboECs étaient comparables à la littérature. De par le choix d’un co-produit issu de la biomasse comme matière première, l’élaboration des carboECs de liqueur noire s’inscrit dans une démarche d’éco-conception. Afin de vérifier cette démarche, les carboECs issus de liqueur noire ont été comparés à des carboECs issus de poly(styrène-co-divinylbenzène), par l’analyse du cycle de vie. Cette étude comparative a montré que le procédé basé sur la liqueur noire aurait un profil écologique plus avantageux que le procédé dit pétrochimique. / Black liquor is a by-product of paper pulp production and is daily produced in large quantities. Non-competitive to the food industry, this wood-based by-product is an important source of biopolymers. Black-liquor based concentrated and stable emulsions were obtained by dispersing an organic phase into black liquor. Among the considered dispersed phases, castor oil and ethylene dichloride were the most suited. Similar materials were prepared by polymerising the concentrated emulsions containing those dispersed phases. The obtained porous monoliths, called polyECs, were compared by life cycle assessment. The results showed that using ethylene dichloride as the dispersed phase was more beneficial for the environment than using castor oil. Through pyrolysis, the polymeric matrix of the polyECs was processed into carbon to produce carboECs. The bio-based porous carbons presented a microporous and a mesoporous structure that is of interest for energy storage, in particularly supercapacitors. The exploratory tests showed that the carboECs efficiency as supercapacitors were similar to what found in literature. The choice of black liquor as the main raw material was made through an eco-design approach. To comfort that approach, the black-liquor-based carboECs were compared to a poly(styrene-co-divinylbenzene)-based carboECs using life cycle assessment. This study showed that using black liquor instead of styrene/divinylbenzene is beneficial.
24

Studium transportu látek v pórovitých materiálech metodou PFG NMR / Investigation of matter transport in porous materials by means of PFG NMR

Peksa, Mikuláš January 2011 (has links)
Title: Investigation of matter transport by means of PFG NMR Author: Mikuláš Peksa Department of low temperature physics Supervisor: doc. RNDr. Jan Lang, Ph.D. Assistant Supervisor: RNDr. Milan Kočiřík, CSc. (ÚFCH JH AV ČR) Abstract: Estimation of transport-structural parameters such as porosity, tortuosity and surface-to-volume ratio of pores in beds of glass beads is the main goal of this study. These parameters were estimated for 5 samples with different distributions of sizes. The second goal is to probe a possibility to use the same approach to describe the self-diffusion in water solution of LiCl confined in two porous materials based on Al2O3 and glass, respectively. The last goal is the measurement of self-diffusion of water molecules in mesoporous geopolymeric material. Its capability of water transport at long scales have been documented. The measurements of apparent self-diffusion coefficients by means of NMR spectroscopy with pulsed field gradients was major methodology of this work. Keywords: porous material, porosity, tortuosity, self-diffusion, NMR
25

NMR detection of liquid dynamics in porous matrices / NMR studier av vätskedynamik i porösa material

Pourmand, Payam January 2012 (has links)
Porous materials or a porous media can be encountered in our everyday life, both in industrial and household systems and in the nature. Generally speaking all solid and semisolid materials are porous to some degree e.g. different dense rock types, plastics etc. Porous materials are constantly finding more and more applications, both in industry and research. Many commercially important process in the industry utilize porous media e.g. flow of fluids through porous media for separation process and porous catalyst supports. This has strongly contributed to the development of porous media with controlled properties, which can be utilized for understanding the behavior of liquids confined in the material, and the morphology of these synthetic materials.This thesis work brings some insight and understanding of porous materials i.e. Controlled Pore Glass (CPG). Report also contains a brief explanation of Nuclear Magnetic Resonance (NMR) spectroscopy, diffusion NMR and other techniques such as Mercury porosimetry.The first part of the thesis is focused on determining the required amount of liquid i.e. octanol needed to achieve full pore saturation for different CPGs with varying pore sizes. This was achieved by taking into account that the transverse relaxation time T2 is sensitive in the ms-ns of motional correlation times, and that there are physical factors in porous material which affect the T2. Second part, diffusion NMR is used to study self-diffusion of octanol confined in CPG, thus bringing some insight on mass transfer limitations within porous systems. The report present results obtained from experiments with NMR and Diffusion NMR, discusses the issues that can arise when investigating porous materials and suggest solutions.
26

Micro-Structure Modelling of Acoustics of Open Porous Material

Lundberg, Eva January 2016 (has links)
Transportation is a large and growing part of the world’s energy consumption. This drives a need for reduced weight of rail vehicles, just as it does for road vehicles. In spite of weight reductions, the vehicle still has to provide the same level of acoustic comfort for the passengers. Porous materials, with more than 90% air, are often included in multi-layer vehicle panels, contributing to acoustic performance without adding much weight. Here the acoustic performance of open cell porous materials, with focus on flow resistivity, is evaluated based on simplified micro-structure models to investigate the effect of anisotropy on the performance In order to evaluate how the redistribution of material affects the flow resistivity, the porosity of the material is kept constant. Two micro-geometries are analysed and compared: the hexahedral model and the tetrakaidecahedron (Kelvin cell). For flow resistivity calculations the solid frame is assumed to be rigid. The models are elongated in one direction to study the influence of micro-structural anisotropy on the macro level flow resistivity. To keep porosity constant, two different approaches are investigated. The first approach is to let strut thickness be uniform and adjust the volume of the cell to a constant ratio compared to the isotropic case. The second approach is to let the strut volume, and cell volume, be constant. For an anisotropic hexahedral cell with uniform strut thickness, the flow resistivity increases substantially with increasing height to width ratio for the hexahedral model, while the flow resistivity for the tetrakaidecahedron model with uniform strut thickness decreases with increasing height to width ratio. For both geometries and constant strut volume, the average flow resistivity is close to the same constant value. For uniform strut thickness the relative volume of anisotropic to isotropic volume is very important. / <p>The work has been carried out within the Centre for ECO<sup>2</sup> Vehicle Design.</p><p></p><p>QC 20160523</p>
27

Mesoporous Silsesquioxanes with High Contents of Surface Amine Groups

Ojo, Kolade O., Golovko, Leonid V., Gomza, Yury P., Vasiliev, Aleksey N. 01 July 2012 (has links)
The objective of this work is the synthesis of highly functionalized hybrid organic/inorganic materials by the polycondensation of bis[3-(trimethoxysilyl) propyl]amine in the presence of surfactants. High contents of amine groups were achieved by carrying out the syntheses without an inorganic cross-linker. The silsesquioxanes obtained had a mesoporous structure. The stability of their porous system in the absence of an inorganic cross-linker was enhanced by the precursor's bridged structure. The material structures were studied by FT-IR spectroscopy, Porosimetry, X-Ray Diffraction and Small Angle X-Ray Scattering methods. A material prepared in the presence of dodecylamine as a template had a higher surface area and narrower pore size distribution while the use of sodium dodecyl sulfate resulted in the formation of mesopores with a wide size distribution. Surface amine groups in silsesquioxanes were accessible for adsorption of small molecules of acidic nature.
28

Studies on Functionalization of Porous Protein Crystals by Immobilizing Organometallic Complexes / 有機金属錯体導入による多孔性蛋白質結晶の機能化に関する研究

Tabe, Hiroyasu 25 May 2015 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19182号 / 工博第4059号 / 新制||工||1626(附属図書館) / 32174 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 北川 進, 教授 杉野目 道紀, 教授 濵地 格 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
29

Multi-physics Properties in Topologically Nanostructured Ferroelectrics / トポロジカルナノ構造を有する強誘電体におけるマルチフィジックス特性

Le, Van Lich 23 September 2016 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19991号 / 工博第4235号 / 新制||工||1655(附属図書館) / 33087 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 北村 隆行, 教授 田畑 修, 教授 鈴木 基史 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
30

NMR detection of liquid dynamics in porous matrices

Pourmand, Payam January 2012 (has links)
Porous materials or a porous media can be encountered in our everyday life, both in industrial and household systems and in the nature. Generally speaking all solid and semisolid materials are porous to some degree e.g. different dense rock types, plastics etc. Porous materials are constantly finding more and more applications, both in industry and research. Many commercially important process in the industry utilize porous media e.g. flow of fluids through porous media for separation process and porous catalyst supports. This has strongly contributed to the development of porous media with controlled properties, which can be utilized for understanding the behavior of liquids confined in the material, and the morphology of these synthetic materials. This thesis work brings some insight and understanding of porous materials i.e. Controlled Pore Glass (CPG). Report also contains a brief explanation of Nuclear Magnetic Resonance (NMR) spectroscopy, diffusion NMR and other techniques such as Mercury porosimetry. The first part of the thesis is focused on determining the required amount of liquid i.e. octanol needed to achieve full pore saturation for different CPGs with varying pore sizes. This was achieved by taking into account that the transverse relaxation time T2 is sensitive in the ms-ns of motional correlation times, and that there are physical factors in porous material which affect the T2. Second part, diffusion NMR is used to study self-diffusion of octanol confined in CPG, thus bringing some insight on mass transfer limitations within porous systems. The report present results obtained from experiments with NMR and Diffusion NMR, discusses the issues that can arise when investigating porous materials and suggest solutions

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