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Ce travail concerne le dopage par des ions actifs et/ou des nanoparticules (NPs) semi-conductrices de CdS et la caractérisation de xérogels de SiO2 poreux obtenus par voie sol-gel. Le but de cette étude est de contribuer à la compréhension de l'effet du dopage sur les propriétés structurales, texturales et optiques du matériau final. Nous avons montré par spectroscopie Raman et absorption-désorption d'azote que l'incorporation d'ions actifs, tels que Cd2+, Pb2+ ou Eu3+, modifie les cinétiques et les mécanismes de la gélification et la densification du réseau de SiO2. La nature même de ces modifications est fonction de la concentration en ions dopants. Dans le cas de l'ion Eu3+, l'analyse a été complétée par la spectroscopie d'émission utilisant cet ion comme sonde luminescente. Des xérogels de SiO2 ont aussi été post-dopés avec des NPs de CdS. La méthode consiste à diffuser dans la matrice poreuse une solution aqueuse contenant les précurseurs de cadmium et du soufre. Les NPs cristallisent ensuite in situ de manière homogène sous traitement thermique. Les spectroscopies d'absorption UV-visible, d'émission et d'excitation ont montré l'influence des niveaux pièges liés à des défauts de surface des NPs sur leurs propriétés optiques et ont mis en évidence un transfert d'énergie lors du co-dopage de SiO2 par CdS :Eu3+. Une deuxième technique de croissance cristalline a été utilisée. Elle consiste à irradier, par un faisceau laser pulsé, les matrices sol-gel contenant les précurseurs de CdS pour former localement des microstructures de NPs. Nous montrons notamment que l'absorption à deux photons permet d'envisager la structuration à l'échelle submicronique des NPs de CdS. / This work concerns the elaboration by sol-gel process and the characterization of porous SiO2 xerogels doped with active ions and/or with semiconducting nanoparticles of CdS. The aim of the study was to contribute to the comprehension of the doping effects on structural and optical properties of the final material. We showed by Raman spectroscopy and nitrogen absorption-desorption that the insertion of active ions, such as Cd2+, Pb2+ or Eu3+, changes the kinetics and the mechanisms of the gelation and densification of the network of SiO2. The choices of the pH and of the concentration of the doping ion have distinct effects on the kinetics. This study was completed by emission spectroscopy using Eu3+ ion as luminescent probe to describe the environment of this ion in the porous matrix. The SiO2 xerogels were post-doped with CdS nanoparticles. The post-doping technique consists in the diffusion of an aqueous solution containing cadmium and sulphur precursors in the porous matrix. The nanoparticles crystallize in situ by heat treatment. The nanoparticle size and their emission properties were determined by UVvisible absorption as well as emission and excitation spectroscopies. The results showed the influence on optical properties of trap levels introduced by the surface defects of nanoparticles and an enhancement of the Eu3+ emission in SiO2 xerogel co-doped with CdS :Eu3+. A second method for the formation of CdS nanoparticles was used. CdS microstructures were created locally by pulsed laser irradiation of sol-gel matrices containing the CdS precursors.

No description available.

L’environnement géostationnaire autour de la Terre présente des conditions complexes influençant les performances ainsi que la durée de vie des satellites. En vol et au cours du temps, les polydiméthylsiloxanes se dégradent ce qui se manifeste par une perte de souplesse, de transparence, ou encore une dégradation de l'état de la surface. Dans ce contexte, le but de cette thèse consiste à étudier l’évolution de la stabilité des polydiméthylsiloxanes en environnement géostationnaire simulé et d’autre part à proposer des solutions qui permettent de limiter la dégradation des propriétés d’intérêts technologiques, optiques en particulier. La stabilisation des polydiméthylsiloxanes soumises aux irradiations UV par l’incorporation de différentes structures d’additifs (Hindered Amine Light Stabilizers, absorbeurs UV, nanocristaux de cellulose) a été étudiée. Une autre approche pour augmenter la stabilité des polydiméthylsiloxanes aux rayonnements UV a été envisagée avec le remplacement du système catalytique actuellement utilisé (catalyseur de Karstedt) par l’emploi de dérivés organométalliques à base de Rhodium ou de Platine. Des solutions concernant la stabilisation de ces polydiméthylsiloxanes aux irradiations H+, comme l’ajout d’additifs tels que le polystyrène, les silsesquioxanes ont également été proposées. / The geostationary environment around Earth is complex which strongly influences the satellites performances and lifetime. In flight and over time, polydimethylsiloxanes exhibit degradations like a loss of flexibility and transparency, or a deterioration of the surface state. In this context, the aim of this work was to study the evolution of polydimethylsiloxanes stability in geostationary environment to find solutions to limit the degradation of interest technological properties, in particular the optical one. The stabilization of silicone resins under UV irradiation has been performed by the incorporation of different additives such as Hindered Amine Light Stabilizers, UV Absorbers and cellulose nanocrystals into the PDMS matrix. Generally, polydimethylsiloxanes networks are obtained by hydrosilylation with highly active Karstedt catalyst. Various organometallics derivatives based on Rhodium and Platinum were studied as alternative catalysts for the cross-linking of polydimethylsiloxane in order to improve the UV stability. Finally, different solutions concerning the stabilization of polydimethylsiloxane to proton irradiation, such as the addition of various additives like polystyrene or silsesquioxanes have been investigated.

M.Tech. / Low-intensity laser irradiation (LILI), also known as photo-biostimulation, is a type of phototherapy which is based on the application of low power monochromatic and coherent light mostly in the wavelength range of 600 to 1 000 nm to injuries and lesions to stimulate healing. LILI has been shown to increase adenosine triphosphate (ATP) synthesis, cell proliferation (Silveira et al., 2007 and 2009; Hawkins and Abrahamse, 2006a) and collagen synthesis, and release of growth factors from cells (Eells et al., 2004). LILI has not been fully embraced and is mainly due to the fact that the biochemical mechanisms underlying the positive effects are not completely understood (Hamblin and Demidova, 2006). Though the mechanisms of photo-biostimulation on a variety of mitochondrial enzymes have been proposed and studied by different researchers, most of the mechanisms are based on oxygen consumption studies and lack direct experimental support (Chen et al., 2008). This project was designed to study the enzyme activity and expression of the mitochondrial respiratory chain complexes (I to V) post-irradiation with a wavelength of 660 nm and a fluence of 5 or 15 J/cm2 in isolated human skin fibroblast cells. Diabetes mellitus (DM) is a group of diseases marked by high levels of blood glucose resulting from defects in insulin production, insulin action or both. It is found worldwide and is estimated to affect 1.1% of the world population (World Health Organization, WHO, 2002). Estimates from 2009 by the International Diabetes Federation suggest that the number of adults with diabetes in the world will expand by 54%, from 284.6 million in 2010 to 438.4 million in 2030. The projected growth for sub-Saharan Africa is 98%, from 12.1 million in 2010 to 23.9 million in 2030 (Mbanya et al., 2010). Though DM is more common in industrialized countries, the trend is changing.