Preparation and characterization of titania-coated polystyrene spheres and hollow titania shells

A procedure has been developed to coat colloidal polystyrene spheres with a smooth and well-defined layer of amorphous titanium dioxide. The thickness of the coating can be easily varied from a few nanometers upward and can be increased further by seeded growth. The resulting composite particles are very monodisperse. The core-shell particles can be turned into spherical hollow titania shells by dissolution of the polystyrene cores in suspension or by calcination of the dried particles in a furnace. Calcination also crystallizes the titania into its anatase form. The coated particles were characterized with electrophoresis, thermogravimetric analysis, X-ray diffraction, electron microscopy, and light scattering. We find that the coating strongly densifies when the particles are dried but that it is not dense and about twice as thick when the particles are still in suspension. Calcination results in spherical shells composed of a dense arrangement of TiO2 (anatase) nanocrystals. This way, we obtained colloidal crystals consisting of hollow shells.