Ultra small angle X-ray scattering investigation of colloidal crystals in latex films

Films obtained from coagulated dispersions of core-shell particles with a rigid thermoplastic core (polystyrene) and a soft elastomeric shell (polymethyl methacrylate-polyethylacrylate) form partially ordered structures which behave like photonic crystals. This behaviour depends on the size of the particles. Samples with different particle size ranging from 200 nm to 300 nm have been characterized by means of Ultra Small Angle X-ray Scattering using synchrotron radiation at HASYLAB beamline BW4. In a layer near the film surface the particles form a regular fcc lattice with the (111) netplanes parallel to the surface. This ordering causes Bragg-like reflections in the scattering pattern. The material in-between the layers shows a scattering contribution caused by strong distance correlation without orientational ordering. From the scattering patterns obtained for different angles between the incoming X-ray beam and the film surface information about the degree of orientational ordering can be derived. (orig.)