SANS studies of polyelectrolyte multilayers on colloidal templates

Polyelectrolyte multilayers adsorbed on colloidal particles were investigated by means of small-angle neutron scattering at contrast matching conditions. Pronounced periodic oscillations related to the latex particle size and to the layer thickness were observed. The scattering data could be well described by assuming a step function density profile of the polyelectrolyte layer taking into account also the instrumental resolution and the polydispersity of the sample. Thus, the thickness of the polyelectrolyte multilayers coating on colloidal particles in an aqueous environment was determined directly. A mean thickness of about 16.6 Å per single polyelectrolyte layer was found for a system consisting of alternate layers of PSS and PAH. It was shown that the layers are rather dense with a water content of 42%. The layer thickness was independent of the curvature of the surface. With increasing number of adsorbed polyelectrolyte layers a slight decrease in the mean thickness per single layer was observed.