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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.
1

Confinement on Soft Materials: Systems Synthesis and Application

Almahdali, Sarah 10 1900 (has links)
Isolating chemically-reactive sites into nanosized compartments is an important mode of control used by Nature to perform chemical transformations with extremely high yields and selectivity. Biological systems are fundamentally organized as bounded and isolated nano- and micro-sized environments featuring distinct localized properties, such as steric crowding, polarity, hydrophobicity, potential for molecular recognition, or pH. Through this compartmentalization, reaction substrates are sequestered away from interfering factors and competing substrates, or are physically prevented from forming alternative products or favoring specific pathways. Inspired by Nature, chemists have explored the rational design and application of various nanocompartments. This work explores three types of nanoconfinement systems capable of catalysis and specific transport: surfactant micelles, block-copolymer micelles, and hollow inorganic nanoparticles. The surfactant micelles are designed as part of a system of self-replicating micelles and are used to show how the chirality of the confinement system effects reaction kinetics. Simple click chemistry between a hydrophilic chiral head and a hydrophobic tail is used to produce an amphiphile under biphasic conditions. Once the product achieves critical micelle concentration, stable micelles can form. These micelles subsequently compartmentalize and pre-concentrate hydrophobic substrates, increasing the reaction rate and resulting in the self-propagation of the micellar structures and their chiralities. The next system explores block-copolymer micelles that are made up of a hydrophobic saturated fluorocarbon block and a hydrophilic block. The amphiphilic copolymers can form aggregates in water and, because of properties unique to the hydrophobic block, this system also increases oxygen solubility in water. Different fluorocarbon monomers are discussed and it was found that the structure of the fluorinated monomer, temperature, and pH effect aggregation behavior and the concentration of dissolved oxygen. Additionally, varying the pH of the system could be used to trigger oxygen release. Similar to the block-copolymer micelles, the hollow inorganic nanoparticles were designed to transport oxygen. Here, hollow silica nanoparticles were designed with a fluorinated interior surface and a hydrophilic exterior. This design allows for highly dispersible nanoparticles in water and facilitates the uptake of saturated fluorocarbon liquids into their cores. Once the saturated fluorocarbon is incorporated, the system can les to increases in oxygen solubility.
2

La nouvelle approche hybride MAX-FEM pour la modélisation thermomécanique des couches minces / The new hybrid approach MAX-FEM for the thermomechanical modelling of thin layers

Ifis, Abderrazzaq 09 April 2014 (has links)
De cette thèse, une nouvelle méthode éléments finis hybride MAX-FEM dédiée à la modélisation thermomécanique des structures avec couches minces a été développée. Cette nouvelle approche se base sur un couplage analytique-numérique de deux méthodes : les Développements Asymptotiques Raccordés (MAE) et la Partition de l'Unité (PUM). Ce couplage consiste à construire l'enrichissement de la PUM par MAE est mène à une forme corrigée de la méthode des éléments finis classique (FEM). Cette correction est obtenue à travers des matrices de correction contenant les informations géométriques et caractéristiques du matériau de la couche mince. Les matrices introduites par l'approche MAX-FEM simplifient son implémentation numérique sous différents codes de calculs (MATLAB, ABAQUS, ...) et permettent l'obtention de la solution globale en un seul calcul. Les résultats obtenus par la MAX-FEM pour des applications 1D et 2D thermomécaniques montrent une très bonne précision avec un temps de calcul minimal et sans raffinement de maillage. De plus, la MAX-FEM surmonte les limitations de la MAE ainsi que celle de la PUM en termes de nombre de calculs, de la sensibilité aux propriétés des matériaux, des conditions aux limites ainsi que l'intégration numérique. Finalement, l'approche MAX-FEM est exploitée pour le développement d'un nouveau protocole expérimental dédié à la caractérisation thermique des couches minces. Ce protocole vise l'identification, de manière simple, de la conductivité thermique de la couche mince après son élaboration et sous les deux régimes transitoire et permanent. L'approche consiste à confronter la nature du transfert thermique d'une éprouvette homogène à une contenant une couche mince. La différence relevée est directement liée à la conductivité thermique de la couche mince. Les résultats obtenus, après réalisation du banc d'essais, montrent une bonne précision de l'approche avec une méthodologie de mesure simple à mettre en oeuvre / This work introduces a new simplified finite elements method MAX-FEM based on hybrid analytical-numerical coupling. This method is intended to the multi-scales analysis of transient thermomechanical behavior of mediums containing thin layers such as bounded and coated structures. The MAX-FEM consists in correcting the classical Finite Elements Method (FEM) by correction matrices taking into account the presence of thin layers without any mesh refinement. The proposed correction is based on the analytical approach of Matched Asymptotic Expansions (MAE) and the numerical method of Partition of Unity Method (PUM). The developed approach can easily implemented under different numerical codes (MATLAB, ABAQUS, ...) and can be used to perform mechanical, thermal and thermomechanical analyses of 1D and 2D bounded and coated structures. The obtained results show a good accuracy with short computation time, and without any required mesh refinement. Also, the developed method overcomes the limitation of the MAE and PUM methods by exploiting the advantages of their coupling. Finally, the MAX-FEM approach was also used to develop an experimental test bench intended to the thermal characterization of thin layers. Indeed, a simple confrontation between the heat transfer in an homogeneous structure and a second structure with thin layer allows identifying the thermal conductivity in both transient and stationary regimes. The test bench is simple to release and the obtained results for brazed structure show a good accuracy of the developed approach.

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