Supervisors: Jean Daillant and Thierry Charitat
Prix de thèse de l’Université de Strasbourg
In this study we report a rigorous calculation of specular and off-specular X ray reflectivity of supported membranes. More precisely, we compute the correlation functions of the membranes only by approximating the interaction potentials as quadratic functions. Thanks to specular reflectivity, we determine the perpendicular structure of the samples, whereas off-specular reflectivity gives access to lateral inhomogeneities of the membranes. By performing simultaneous analysis, we characterize both structure and parameters of the fluctuation spectrum : tension, rigidity and interaction potentials. By studying single supported bilayers, we measure for the first time the effective microscopic tension related to protrusions inside the membrane (about 80 mN/m). Long range fluctuations are determined by moving the membrane away from the substrate by the addition of an adsorbed membrane. Therefore we precisely measure the interaction potential between neutral membranes in a state of equilibrium. Non equilibrium fluctuations are studied by applying an electric field. For the first time we show that the field induces a negative electrostatic tension on the order of 1 mN/m and a positive rigidity of about 100 kBT. We finally begin the study of more complex interactions by analysing the signal of charged membranes by X ray and neutron reflectivity.