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X-ray scattering studies of structure and dynamics of surfaces and interfaces of polymeric liquids


Thermally excited capillary waves are present and dominate the morphology and dynamics at the surfaces and interfaces of polymer films in a molten state. A statistical description of the capillary waves in terms of the temporal and lateral position dependent height-height correlation functions is directly related to the scattering structure factor. This can be calculated using surface scattering theories and measured by surface sensitive diffuse scattering techniques. A large part of this thesis is devoted to the investigation of the surface and interfacial dynamics of supported single layer polystyrene and bilayer polystyrene/poly(4-bromo styrene) films using x-ray photon correlation spectroscopy (XPCS), a recently developed time-resolved coherent scattering technique on high-brilliance third-generation synchrotron radiation facilities. The static properties, such as thickness, surface tension, and interfacial width, can be obtained by conventional reflectivity and static diffuse scattering experiments. Apart from the surface and interfacial capillary waves, inhomogeneities induced by thermal density fluctuations in the interior of the film also contribute to the total diffuse scattering. Therefore, a bulk scattering theory for thin film geometry is developed and compared with the experimental results from supported molten polystyrene films. We also present the first attempt to probe the structure and dynamics of single lipid bilayers consisting of phase-separated raft- like domains using x-ray and neutron scattering techniques

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