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Microscopie à l'angle de Brewster : transitions de phases et défauts d'orientation dans des films monomoléculairess

Abstract : Microscopy at the Brewster angle is a new powerful technique for the study of monolayers at the free surface of water. Taking advantage of the reflectivity properties of an interface, it is sensitive to the thickness, density and anisotopy of the films. This technique was used to study the phase transitions that sometimes occur during the formation of films adsorbed at the surface of aqueous solutionsof amphiphiles. The number, nature and morphology of these phases depend on experimental conditions, including pH.We thus were able to follow the formation and evolution of structures in which the tilt of the molecules creates an observable optical anisotropy. The corresponding phases are "locked tilted mesophases", i.e.the molecular direction is fixed with respect to intermolecular directions. We observed several orientational defects morphologies, includind star structures, which were modeled by continuum elasticity theory developped for thin films of smectic liquid crystals. We also observed structures consisting of kinked defects lines, spirals or stripes of constant width. Layers of a polymer (PDMS) at the free surface of water were also studied. We observed a lateral separation into domains of different surface density, both in the monolayer and in multilayer regimes
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Submitted on : Tuesday, February 19, 2002 - 7:29:46 PM
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  • HAL Id : tel-00001113, version 1


Sylvie Hénon. Microscopie à l'angle de Brewster : transitions de phases et défauts d'orientation dans des films monomoléculairess. Analyse de données, Statistiques et Probabilités []. Université Pierre et Marie Curie - Paris VI, 1993. Français. ⟨tel-00001113⟩



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