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Nouvelles études structurales de cristaux liquides par réflectivité et diffraction résonante des rayons X

Abstract : This memory presents three structural studies of smectic Liquid Crystals by reflectivity and resonant diffraction of X-rays. It is divided in five chapters. In the first a short introduction to Liquid Crystals is given. In particular, the smectic phases that are the object of this study are presented. The second chapter is consecrated to the X-ray experimental techniques that were used in this work. The three last chapters present the works on which this thesis can be divided. Chapter three demonstrates on free-standing films of MHPOBC (historic liquid crystal that possesses the antiferroelectric subphases) the possibility to extend the technique of resonant X-ray diffraction to liquid crystals without resonant element. In the fourth chapter the structure of the B2 liquid crystal phase of bent-core molecules (or banana molecules) is elucidated by using resonant X-ray diffraction combined with polarization analysis of the diffracted beam. A model of the polarization of the resonant beam diffracted by four different structures proposed for the B2 phase is developed in this chapter. In the fifth chapter a smectic binary mixture presenting a very original critical point of phase separation is studied by X-ray reflectivity and optical microscopy. A concentration gradient in the direction perpendicular to the plane of the film seems to be induced by the free-standing film geometry. The results of a simplified model of the system are compatible with this interpretation.
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Submitted on : Wednesday, March 19, 2008 - 10:31:59 AM
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Paulo Fernandes. Nouvelles études structurales de cristaux liquides par réflectivité et diffraction résonante des rayons X. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Sciences et Technologies - Bordeaux I, 2007. Français. ⟨tel-00265389⟩

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