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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

Bi-metallic Catalyst for Hydrogen Sorption of Magnesium Hydride

Zahiri-Sabzevar, Beniamin Unknown Date
No description available.
2

Investigação de ablação a laser no regime de femtossegundo em materiais homogêneos e estruturados / Investigation of the femtosecond laser ablation on homogeneous and structured materials

Nicolodelli, Gustavo 31 March 2011 (has links)
Embora a ablação a laser venha sendo bastante utilizada em materiais em geral, pouco é entendido sobre o comportamento deste processo perto de uma interface separando dois materiais distintos. Neste contexto, o principal objetivo deste trabalho foi realizar um estudo macroscópico e microscópico dos processos que envolvem a ablação a laser em regime de femtossegundos em materiais homogêneos e estruturados. No caso de materiais estruturados, o estudo focou-se em uma situação de interface, na qual ocorrem mudanças nas propriedades de ablação. Baseado nos resultados, nós pretendemos obter subsídios científicos para entender as aplicações da ablação em regime de pulsos ultracurtos para estruturas estratificadas, tais como de dentes, ossos, interface resina-dente, dente-metal, e outras. Diferentes técnicas experimentais foram idealizadas para determinar a progressão da ablação dentro do material e obter dados extraídos da superfície. Utilizando luz espalhada de uma fonte externa, o processo de ablação foi temporalmente monitorado, permitindo determinar a velocidade de ablação em materiais transparentes, assim como perfis típicos de ablação nestes materiais. Em um segundo experimento, nosso estudo permitiu quantificar a variação da geometria de ablação perto de uma interface separando dois materiais distintos. Nossos dados foram suficientes para prever a ocorrência de uma descontinuidade no perfil da ablação entre dois meios: resina A e resina B, mostrando uma repentina descontinuidade do diâmetro da cavidade ablacionada. Adicionalmente, foi realizada uma análise dos aspectos morfológicos de diferentes tecidos biológicos irradiados e nosso estudo mostrou a eficiência da ablação utilizando laser de femtossegundos no processamento de tecidos duros e a possibilidade de utilizar esses sistemas sem causar danos térmicos e mecânicos nos tecidos remanescentes. Finalmente nós aplicamos a microperfuração a laser para produzir micro-poros na superfície de tecidos biológicos (fígados), melhorando a penetração do medicamento ALA e a aumentando a profundidade de tratamento. / Although laser ablation has been long used in general materials, little is known regarding the behavior of theses process near an interface separating two distinct materials. In this context, the main aim of this work was to perform a microscopic and macroscopic study of the processes that include femtosecond laser ablation in homogeneous and/or structured materials. In the case of structured materials, the study focused on an interface situation, in which sudden changes occurred in the properties. Based on the results, we aimed to obtain scientific subsidies to understand the application of ultrashort pulses to stratified structures, such as teeth, bones, resin-teeth or metal-teeth interface, and others. Distinct experimental techniques were used to determinate the ablation progression into the materials and to obtain data extracted from their surface. By using the scattered light from an external source, the ablation process was monitored temporally, allowing to determine the velocity of ablation in transparent materials, besides determining the typical profiles of ablated cavities in these materials. In a second experiment, our study allowed quantifying the overall variation in the ablation geometry that takes place on the interface of two different materials. Our data were sufficient to predict the occurrence of a discontinuity in the ablation profile on the interface between two media: resin A and resin B, showing a sudden discontinuity of the ablated cavity diameter. In addition, an analysis of the morphological aspects of different biological tissues irradiated by femtosecond laser pulses was performed and a comparative study showed the ablation efficiency of the femtosecond lasers in hard tissues processing and the possibility of using these systems with no thermal and mechanic damage. Finally, we applied a laser micromachining producing micro-pores on the tissue surface, improving the ALA penetration and increasing the treatment depth.
3

Investigação de ablação a laser no regime de femtossegundo em materiais homogêneos e estruturados / Investigation of the femtosecond laser ablation on homogeneous and structured materials

Gustavo Nicolodelli 31 March 2011 (has links)
Embora a ablação a laser venha sendo bastante utilizada em materiais em geral, pouco é entendido sobre o comportamento deste processo perto de uma interface separando dois materiais distintos. Neste contexto, o principal objetivo deste trabalho foi realizar um estudo macroscópico e microscópico dos processos que envolvem a ablação a laser em regime de femtossegundos em materiais homogêneos e estruturados. No caso de materiais estruturados, o estudo focou-se em uma situação de interface, na qual ocorrem mudanças nas propriedades de ablação. Baseado nos resultados, nós pretendemos obter subsídios científicos para entender as aplicações da ablação em regime de pulsos ultracurtos para estruturas estratificadas, tais como de dentes, ossos, interface resina-dente, dente-metal, e outras. Diferentes técnicas experimentais foram idealizadas para determinar a progressão da ablação dentro do material e obter dados extraídos da superfície. Utilizando luz espalhada de uma fonte externa, o processo de ablação foi temporalmente monitorado, permitindo determinar a velocidade de ablação em materiais transparentes, assim como perfis típicos de ablação nestes materiais. Em um segundo experimento, nosso estudo permitiu quantificar a variação da geometria de ablação perto de uma interface separando dois materiais distintos. Nossos dados foram suficientes para prever a ocorrência de uma descontinuidade no perfil da ablação entre dois meios: resina A e resina B, mostrando uma repentina descontinuidade do diâmetro da cavidade ablacionada. Adicionalmente, foi realizada uma análise dos aspectos morfológicos de diferentes tecidos biológicos irradiados e nosso estudo mostrou a eficiência da ablação utilizando laser de femtossegundos no processamento de tecidos duros e a possibilidade de utilizar esses sistemas sem causar danos térmicos e mecânicos nos tecidos remanescentes. Finalmente nós aplicamos a microperfuração a laser para produzir micro-poros na superfície de tecidos biológicos (fígados), melhorando a penetração do medicamento ALA e a aumentando a profundidade de tratamento. / Although laser ablation has been long used in general materials, little is known regarding the behavior of theses process near an interface separating two distinct materials. In this context, the main aim of this work was to perform a microscopic and macroscopic study of the processes that include femtosecond laser ablation in homogeneous and/or structured materials. In the case of structured materials, the study focused on an interface situation, in which sudden changes occurred in the properties. Based on the results, we aimed to obtain scientific subsidies to understand the application of ultrashort pulses to stratified structures, such as teeth, bones, resin-teeth or metal-teeth interface, and others. Distinct experimental techniques were used to determinate the ablation progression into the materials and to obtain data extracted from their surface. By using the scattered light from an external source, the ablation process was monitored temporally, allowing to determine the velocity of ablation in transparent materials, besides determining the typical profiles of ablated cavities in these materials. In a second experiment, our study allowed quantifying the overall variation in the ablation geometry that takes place on the interface of two different materials. Our data were sufficient to predict the occurrence of a discontinuity in the ablation profile on the interface between two media: resin A and resin B, showing a sudden discontinuity of the ablated cavity diameter. In addition, an analysis of the morphological aspects of different biological tissues irradiated by femtosecond laser pulses was performed and a comparative study showed the ablation efficiency of the femtosecond lasers in hard tissues processing and the possibility of using these systems with no thermal and mechanic damage. Finally, we applied a laser micromachining producing micro-pores on the tissue surface, improving the ALA penetration and increasing the treatment depth.
4

Shear stress distribution within narrowly constrained structured grains and granulated powder beds

Antony, S.J., Al-Sharabi, M., Rahmanian, Nejat, Barakat, T. 22 October 2015 (has links)
An experimental study is presented here to understand the stress transmission characteristics under different geometrical arrangements of particulates inside a narrow chamber subjected to axial compression loading. The multi-grain systems considered here are face-centred, simple cubic and poly-dispersed structures, as well as inclusions embedded inside seeded, unseeded and cohesive powder bed of Durcal (calcium carbonate). The distribution of the maximum shear stress, direction of the major principal stress and shear stress concentration factor were obtained using photo stress analysis tomography (PSAT). The results show that the maximum shear stress distribution in the simple cubic structure is chain-like and self-repetitive, i.e., a single grain behaviour is representative of the whole system. This is not the case in the case of other granular packing. In the case of the inclusion surrounded by powder media, the maximum shear stress distribution in the inclusion occurs through ring-like structures, which are different from those observed in the structured granular packing. This tendency increases for an increase in the cohesivity of the surrounding particulates. In the granular systems, the direction of the major principal stress is mostly orthogonal to the direction of loading except in some particles in the random granular packing. In the case of inclusion surrounded by Durcal particulates, the directional of the major principal stress acts along the direction of the axial loading except in the ring region where this tends to be oblique to the direction of axial loading. Estimates of the shear stress concentration factor (k) show that, k tends to be independent of the structural arrangement of granular packing at higher load levels. In the case of inclusion surrounded by powder bed, k for the seeded granulated particulate bed is mostly independent of the external load levels. In the case of unseeded particulate (granulated) bed, a fluctuation in k is observed with the loading level. This suggests that the seeded granules could distribute stresses in a stable manner without much change in the nature of shear stress-transmitting fabric of the particulate contacts under external loading. An increase in the cohesion of particulate bed results in more plastic deformation as shown by the differential shear stress concentration factor. The results reported in this study show the usefulness of optical stress analysis to shed some scientific lights on unravelling some of the complexities of particulate systems under different structural arrangements of grains and surrounding conditions of the inclusions in particulate media.
5

Conception et optimisation de piles enzymatiques glucose-O2 pour la gestion de puissance / Design and optimization of glucose-O2 enzymatic cells for power management

Abreu, Caroline 16 November 2017 (has links)
Ce mémoire est consacré à l’optimisation de la connexion enzymatique pour l’oxydation du glucose et la réduction du dioxygène dans une matrice de nanotubes de carbone (CNTs) sous forme de compression dans les biopiles à glucose, et à l’assemblage de biopiles dans un système à flux. Dans un premier temps, le transfert électronique indirect de la glucose oxydase (GOx) et de la glucose déshydrogénase FAD-dépendante (FADGDH) est optimisé dans une matrice nanostructurée de CNTs contenant différents médiateurs rédox. Ces bioanodes ont pu être combinées avec des biocathodes similaires à bases d’enzymes à cuivre, la laccase (Lac) et la bilirubine oxydase (BOD). La biopile GOx-NQ/Lac présente une puissance de l’ordre de 150 µW sous 150 mmol.L-1 de glucose et la biopile GOx-NQ/BOD orientée par la PP IX, quant à elle, possède une puissance de l’ordre de 0,5 mW sous 5 mmol.L-1 de glucose. Cette biopile présente une très bonne alternative à l’implantable ou à l’alimentation d’un appareil électronique à faible demande énergétique. La partie suivante concerne l’élaboration d’un design de biopile à flux optimisant la diffusion du substrat à l’intérieur de la bioélectrode. De ce fait, plusieurs systèmes de biopiles GOx-NQ/BOD à flux de substrat ont été étudiés. La configuration de flux traversant a permis d’obtenir une puissance de l’ordre de 1 mW sous 5 mmol.L-1 de glucose et oxygène dissous. La possibilité d’utiliser cette pile en décharge continue ou en cycle de charge/décharge a été étudiée. Ce système de biopile à flux de glucose a permis également d’associer plusieurs biopiles en série ou en parallèle. Ainsi, l’alimentation d’un minuteur et d’un test d’ovulation a pu être réalisée à l’aide de biopiles associées en série. D’autre part, l’utilisation d’un circuit de gestion de l’énergie a permis d’alimenter un capteur de température en stockant l’énergie produite par deux biopiles connectées en série. Cette partie se consacre également à une biopile basée sur l’association de la HRP à la cathode et la GOx-NQ à l’anode. Ce système est très intéressant puisque grâce à la maitrise du sens du flux de notre substrat, le peroxyde d’hydrogène formé par l’anode peut être alors consommé par la cathode. Cette pile s’est montrée parfaitement opérationnelle en condition physiologique et a abouti à l’obtention de puissances de l’ordre de 0,8 mW. / This work is devoted to the optimization of the enzymatic connection for the oxidation of glucose and the reduction of dioxygen in a matrix of carbon nanotubes (CNTs) in the form of compression in glucose biofuel cells, and the assembly of biofuel cells in a flow system.First, mediated electron transfer of glucose oxidase (GOx) and FAD-dependent glucose dehydrogenase (FADGDH) is optimized in a nanostructured CNTs matrix containing different redox mediators. These bioanodes could be combined with similar biocathodes with copper enzyme bases, laccase (Lac) and bilirubin oxidase (BOD). The GOx-NQ/Lac biofuel cell has a power of the order of 150 μW under 150 mmol L-1 of glucose and the biofuel cell GOx-NQ/BOD oriented by the PP IX, order of 0.5 mW under 5 mmol L-1 of glucose. This biofuel cell presents a very good alternative to the implantable or to the supply of an electronic device with low energy demand.The next part concerns the development of a biofuel cell design with flux optimizing the diffusion of the substrate inside the bioelectrode. As a result, several GOx-NQ/BOD flow systems have been studied. The flow-through configuration made it possible to obtain a power of the order of 1 mW under 5 mmol L-1 of glucose and dissolved oxygen. The possibility of using this battery in continuous discharge or in charge/discharge cycle has been studied. This biofuel cell system with a glucose flow has also made it possible to associate several biofuel cells in series or in parallel. Thus, the power supply of a timer and an ovulation test could be realised using associated biofuel cells in series. The use of an energy management circuit made it possible to supply a temperature sensor by storing the energy produced by two biofuel cells connected in series.Moreover, this part is about another biofuel cell based on the association of HRP with the cathode and the GOx-NQ at the anode. This system is very interesting because, thanks to the control of the flow direction of our substrate, the hydrogen peroxide formed by the anode can then be consumed by the cathode. This stack was perfectly operational in physiological condition and led to the achievement of powers of the order of 0.8 mW.
6

Projeto primeiro, aprender!: estudo de caso em quatro escolas públicas estaduais do Ceará

Brito, Márcio Pereira de 30 October 2012 (has links)
Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-04-06T11:57:32Z No. of bitstreams: 1 marciopereiradebrito.pdf: 851720 bytes, checksum: caad7711f165557a7dc6352a26b73cc4 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-04-24T04:13:02Z (GMT) No. of bitstreams: 1 marciopereiradebrito.pdf: 851720 bytes, checksum: caad7711f165557a7dc6352a26b73cc4 (MD5) / Made available in DSpace on 2016-04-24T04:13:02Z (GMT). No. of bitstreams: 1 marciopereiradebrito.pdf: 851720 bytes, checksum: caad7711f165557a7dc6352a26b73cc4 (MD5) Previous issue date: 2012-10-30 / O presente trabalho, intitulado Projeto Primeiro, Aprender!: estudo de caso em quatro escolas públicas estaduais do Ceará, foi desenvolvido no Programa de Pós Graduação Profissional em Gestão e Avaliação da Educação Pública do CAED/UFJF para obtenção do título de mestre. Este trabalho teve como objetivo analisar o processo de implementação e gerência do Projeto Primeiro, Aprender! pela gestão escolar, bem como a proposição de um Plano de Ação Educacional. O Primeiro, Aprender! é um projeto da Secretaria Estadual de Educação do Ceará, de intervenção pedagógica, direcionado para a superação de defasagens dos alunos que ingressam no ensino médio. Este estudo justifica-se, pois não há ainda estudos que apresentem os efeitos surtidos pela implementação do projeto no Estado. Para a realização deste estudo utilizamos como metodologia a análise documental, a pesquisa bibliográfica, aplicamos questionários com os professores envolvidos no projeto, bem como entrevistas semiestruturadas com os gestores escolares e da regional de ensino do Ceará com o objetivo de compreender como tem ocorrido a implementação do projeto em quatro escolas públicas estaduais. Para análise dos dados obtidos, nos apropriamos de referenciais teóricos para a discussão de programas de intervenção pedagógica (Lima, 2011), de implementação de políticas públicas educacionais (Mainardes, 2006), e, dentre outros temas, a formação e atuação do gestor escolar (Luck, 2000; 2009). Valemo-nos, ainda, de pesquisas desenvolvidas pela Fundação Lemann (2008) que faz análise dos usos de materiais estruturados no estado de São Paulo. Como principais resultados, identificamos a necessidade de uma revisão do material e de uma formação dos gestores para a implementação do projeto nas escolas. Neste sentido, o Plano de Ação Educacional apresentado propõe ações para a formação e melhor atuação do gestor escolar, tornando-o protagonista do processo de implementação do projeto e liderança da equipe escolar na execução da proposta. / This work, entitled First Draft, Learn!: Case study in four public schools of Ceará, was developed in the Graduate Program in Professional Management and Evaluation of Public Education CAEd / UFJF to obtain the title of Master. This study aimed to analyze the process of implementation and management of the Project First, Learn! by school management as well as the proposition of an Educational Action Plan. First, Learn! is a project of the State Department of Education of Ceará, for pedagogical intervention, aimed at overcoming lags of students who enter high school. This study is justified because there are no studies yet that show the effects assorted for project implementation in the State. For this study we used as a methodology to document analysis, bibliographic research, we apply questionnaires with teachers involved in the project, as well as semi-structured interviews with school managers and regional education Ceará with the aim of understanding as has been the implementation project in four public schools. For data analysis, we appropriate theoretical frameworks for discussion of pedagogical intervention programs (Lima, 2011), implementation of educational policies (Mainardes, 2006), and, among other things, the formation and performance of the school manager (Luck, 2000, 2009). We have used also research developed by the Lemann Foundation (2008) which makes analysis of the uses of structured materials in the state of São Paulo. As main results, we identified the necessity of a review of the material and training of managers for project implementation in schools. Accordingly, the Plan of Action Education presented proposes actions for training and better performance of the school manager, becoming the protagonist of the process of project implementation and leadership of the school staff in implementing the proposal.
7

Modelling stain rate sensitive nanomaterials' mechanical properties: the effects of varying definitions

Sob, Peter Baonhe 06 1900 (has links)
M. Tech. (Mechanical Engineering, Faculty of Engineering and Technology): Vaal University of Technology / Presently there exist a lot of controversies about the mechanical properties of nanomaterials. Several convincing reasons and justifications have been put forward for the controversies. Some of the reasons are varying processing routes, varying ways of defining equations, varying grain sizes, varying internal constituent structures, varying techniques of imposing strain on the specimen etc. It is therefore necessary for scientists, engineers and technologists to come up with a clearer way of defining and dealing with nanomaterials’ mechanical properties. The parameters of the internal constituent structures of nanomaterials are random in nature with random spatial patterns. So they can best be studied using random processes, specifically as stochastic processes. In this dissertation the tools of stochastic processes have been used as they offer a better approach to understand and analyse random processes. This research adopts the approach of ascertaining the correct mathematical models to be used for experimentation and modelling. After a thorough literature survey it was observed that size and temperature are two important parameters that must be considered in selecting the relevant mathematical definitions for nanomaterials’ mechanical properties. Temperature has a vital role to play during grain refinement since all severe plastic deformation involves thermomechanical processes. The second task performed in this research is to develop the mathematical formulations based on the experimental observation of 2-D grains and 3-D grains deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing. The experimental observations revealed that grains deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing are elongated when observed from the rolling direction, and transverse direction, and equiaxed when observed from the normal direction. In this dissertation, the different experimental observations for the grain size variants during grain refinement were established for 2-D and 3-D grains. This led to the development of a stochastic model of grain-elongation for 2-D and 3-D grains. The third task was experimentations and validation of proposed models. Accumulative Roll-Bonding, Equal Channel Angular Pressing and mechanical testing (tensile test) experiments were performed. The effect of size on elongation and material properties were studied to validate the developed models since size has a major effect on material’s properties. The fourth task was obtaining results and discussion of theoretical developed models and experimental results. The following facts were experimentally observed and also revealed by the models. Different approaches of measuring grain size reveal different strains that cannot be directly obtained from plots of the corresponding grain sizes. Grain elongation evolved as small values for larger grains, but became larger for smaller grains. Material properties increased with elongation reaching a maximum and started decreasing as is evident in the Hall-Petch to the Reverse Hall-Petch Relationship. This was alluded to the fact that extreme plastic straining led to distorted structures where grain boundaries and curvatures were in “non-equilibrium” states. Overall, this dissertation contributed new knowledge to the body of knowledge of nanomaterials’ mechanical properties in a number of ways. The major contributions to the body of knowledge by his study can be summarized as follows: (1) The study has contributed in developing a model of elongation for 2-D grain and 3-D grains. It has been generally reported by researchers that materials deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing are generally elongated but none of these researchers have developed a model of elongation. Elongation revealed more information about “size” during grain refinement. (2) The Transmission Electron Microscopy revealed the grain shape in three directions. The rolling direction or sliding direction, the normal direction and the transverse direction. Most developed models ignored the different approaches of measuring nanomaterials’ mechanical properties. Most existing models dealt only with the equivalent radius measurement during grain refinement. In this dissertation, the different approaches of measuring nanomaterials’ mechanical properties have been considered in the developed models. From this dissertation an accurate correlation can be made from microscopy results and theoretical results. (3) This research has shown that most of the published results on nanomaterials’ mechanical properties may be correct although controversies exist when comparing the different results. This research has also shown that researchers might have considered different approaches to measure nanomaterials’ mechanical properties. The reason for different results is due to different approaches of measuring nanomaterials’ mechanical properties as revealed in this research. Since different approaches of measuring nanomaterials’ mechanical properties led to different obtained results, this justify that most published results of nanomaterials’ mechanical properties may be correct. This dissertation revealed more properties of nanomaterials that are ignored by the models that considered only the equivalent length. (4) This research has contributed to the understanding of nanomaterials controversies when comparing results from different researchers.
8

Evolution and Environmental Degradation of Superhydrophobic Aspen and Black Locust Leaf Surfaces

Tranquada, George Christopher 17 July 2013 (has links)
The current study is focused on the characterization of four natural leaf species (quaking, bigtooth and columnar european aspen as well as black locust) possessing a unique dual-scale cuticle structure composed of micro- and nano-scale asperities, which are able to effectively resist wetting (superhydrophobic), characteristic of The Lotus Effect. Scanning Electron Microscopy (SEM) was used to track the growth and evolution of their distinctive nano-scale epicuticular wax (ECW) morphologies over one full growing season. In addition, the stability of their superhydrophobic property was tested in various environments. It was determined that the long-term stability of these surfaces is tentatively linked to various environmental stress factors. Specifically, a combination of high temperature and humidity caused the degradation of nano-scale asperities and loss of the superhydrophobic property. The dual-scale surface structure was found to provide a suitable template for the design of future superhydrophobic engineering materials.
9

Evolution and Environmental Degradation of Superhydrophobic Aspen and Black Locust Leaf Surfaces

Tranquada, George Christopher 17 July 2013 (has links)
The current study is focused on the characterization of four natural leaf species (quaking, bigtooth and columnar european aspen as well as black locust) possessing a unique dual-scale cuticle structure composed of micro- and nano-scale asperities, which are able to effectively resist wetting (superhydrophobic), characteristic of The Lotus Effect. Scanning Electron Microscopy (SEM) was used to track the growth and evolution of their distinctive nano-scale epicuticular wax (ECW) morphologies over one full growing season. In addition, the stability of their superhydrophobic property was tested in various environments. It was determined that the long-term stability of these surfaces is tentatively linked to various environmental stress factors. Specifically, a combination of high temperature and humidity caused the degradation of nano-scale asperities and loss of the superhydrophobic property. The dual-scale surface structure was found to provide a suitable template for the design of future superhydrophobic engineering materials.
10

Auto-assemblage de matériaux méso-structurés / Self-assembly of meso-structured materials

Schmitt, Julien 06 October 2014 (has links)
Les matériaux méso-structurés sont des matériaux à porosité contrôlée, issus de synthèses de chimie sol/gel entre micelles de tensioactifs et précurseur inorganique, le plus souvent de silice. Parmi ces matériaux, le SBA-15, formé en milieu super-acide à partir de P123 (un copolymère tribloc) comme tensioactif et de TEOS comme précurseur inorganique de silice, est un des plus étudiés. La synthèse de ce matériau a été étudiée par diffusion des rayons X à petits angles (SAXS) in situ, et a permis de décrire qualitativement et quantitativement les mécanismes d’auto-assemblages entre micelles de tensioactifs et particules silicatées. Spécifiquement, nos résultats ont montré que l’hydrolyse-condensation du TEOS en solution a permis la formation d’oligomères de silice, qui interagissent avec la couronne des micelles sphériques de P123, pour progressivement former des micelles hybrides cylindriques organiques/inorganiques, qui vont ensuite précipiter en une mésophase hybride 2D-hexagonale. Ce modèle de synthèse est appelé « transition sphères-cylindres ». De plus, afin de comprendre les mécanismes de formation du matériau à toutes les échelles, nous avons étudié l’influence des conditions de synthèse sur la morphologie des grains de matériau méso-structurés. En effet, nous avons montré que sans agitation pendant la synthèse, les grains de matériaux présentent une forme d’équilibre qui dépend fortement de la température de synthèse. En fonction de la température, il est donc possible de former des matériaux hybrides de forme grains de riz, bâtons (courts ou longs) ou mêmes sous forme de tores. Nous proposons un modèle théorique qui permet d’expliquer l’ensemble des morphologies observées, en fonction des tensions de surfaces et des énergies de courbures de cristal-liquide 2D-hexagonal lors de la précipitation de la mésophase hybride. Nous appuyons ce modèle théorique sur des études en diffusion des rayons X à très petits angles (USAXS), qui permettent d’étudier la croissance des grains. Grâce à ces études, nous proposons une description très complète de la formation du matériau SBA-15. Fort de ces connaissances, nous avons pu, grâce à de nouvelles études de SAXS in situ, appliquer le modèle de précipitation de type « transition sphères-cylindres » à d’autres matériaux, issus de tensioactifs non-ioniques fluorés, et ainsi expliquer la formation de matériaux dits « bimodaux », c’est-à-dire issus d’un mélange entre P123 et un tensioactif fluoré(Rf₈(EO)₉ et qui présentent deux ordres poreux bien définis. Enfin, nous avons cherché à utiliser nos connaissances pour la fabrication de matériaux innovants, en remplaçant la solution micellaire par des émulsions dopées en nanoparticules d’or (NPs), afin de fabriquer des matériaux hybrides dopés en NPs. / Meso-structured materials are materials with a well-controlled porosity, designed from sol/gel syntheses between surfactant micelles and an inorganic precursor, most often a silica precursor. Among them, the SBA-15 material, formed in super-acid solution from P123 (a tri-block copolymer) as surfactant and TEOS a silica precursor, is one of the most studied. Synthesis of this material has been studied by in situ Small Angle X-Ray Scattering (SAXS), which allowed to describe both qualitatively and quantitatively the self-assembly mechanisms between surfactant micelles and silica particles. In details, our results showed that TEOS hydrolysis-condensation allow the formation of silica oligomers that interact with the corona of the spherical micelles of P123, and progressively the micelles reshape in hybrid organic/inorganic cylindrical micelles. The hybrid micelles, first free in solution, eventually precipitate in a hybrid 2D-hexagonal mesophase. This model of synthesis is called “sphere-to-rod transition”. Moreover, in order to understand the material mechanisms of formation at every length scales, we studied the influence of the synthesis conditions on the morphology of the meso-structured material grains. Indeed, in agreement with a previous study, our results show that if the synthesis is made without stirring, the material grains has an equilibrium shape that strongly depends on the synthesis temperature. By changing the temperature, one can form hybrid materials with a “rice grain” shape, or a (short or long) rod shape, or even a torus shape. We propose a theoretical model to explain all the observed morphologies, model that takes into account surface tensions and curvature energy of the newly formed 2D-hexagonal liquid-crystal at the precipitation of the hybrid mesophase. We measured the nucleation and growth of the grains by Ultra Small Angle X-Ray Scattering (USAXS). Thanks to all these studies, we present a complete description of the formation of the SBA-15 material. Our knowledge were used to describe new in situ SAXS measurements of new materials: our “sphere-to-rod transition” model was able to describe the formation of two materials, form two fluorinated surfactants and allowed to explain the formation of a “bimodal” material, which means a material with two well-defined porous order, that is synthesized from a mix of two surfactant (P123 and (Rf₈(EO)₉). Finally, we tried to use our knowledge to form innovative materials, by replacing the micellar solution as template by an emulsion doped in gold nanoparticles (NPs) to form hybrid materials doped in NPs.

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