Résumé
This PhD work concerns the understanding of the self-assembling mechanisms of organic-inorganic hybrid silicas obtained via sol-gel route. The molecular precursors consist of an inorganic substructure with triethoxysilyl groups associated to an organic substructure which provides the self-organization properties. Two precursors are studied in this work. The first one has a phenyl group as organic substructure between two urea groups which favour the selfassembly via intermolecular H-bonds during the synthesis of the material in solution. The second one is a monosilylated ureidopyrimidinone derivative that initially self-assembles in dimers in solution precluding its capacity to interact by intermolecular H-bonds during the sol-gel synthesis. A fundamental study of mid and far infrared vibrational dynamic together with ab initio calculations of the two precursors are carried out. The influence of H-bond on infrared vibrational dynamic is studied. These results are then used to monitor the competition between covalent and non covalent interactions during the self-organization process. An in situ experimental study which combines optical microscopy, light scattering and infrared spectroscopy gives a better insight into the self-assembling kinetics of the two precursors. We propose a structuring model in solution dominated by activation barriers governed by H-bonds. The structure of the hybrid material in solid phase is determined from a structural study based on X-Ray diffraction. The investigation under pressure of the hybrid materials obtained after heating and freeze-drying shows that both the short order arrangement (H-bonds, polycondensation rate) and the mesoscopic structure strongly depend on this step.