Preparation of core-shell structures by coating polystyrene microparticles with nanoparticles of TiO2 and Fe2O3

Polystyrene microparticles were coated with one, two and even three different shells of oxide nanoparticles. The coatings of two types of latex were compared. The first one consisted of sulfate-functionalized polystyrene (S-PS) particles of 1.0 μm, prepared by the procedure in [1]. The second type of latex was made up of 2 μm polystyrene carboxy-(C-PS) particles. Both types of latex present a polydispersity index PI < 0.05, the particles are hydrophobic and the latexes are electrostatically stabilized The density of the is ρPS = 1.054 g/cm3, the refractive index n = 1.59 and the surface charge density is σS-PS = 9 μC/cm2 and σC-PS = 15 μC/cm2.
Regarding the oxides, three different types of nanoparticles were synthesized: positive TiO2
[2], negative TiO2 [3-4] and positive Fe3O4 nanoparticles [5]. The size of the nanoparticles can be modified by controlling the time of reaction. While the charge of the TiO2 nanoparticles depends of the pH, negative Fe3O4 particles could not be prepared, due to their small stability. The oxide nanoparticles were characterized by thermogravimetry, Transmission Electron Microscopy (TEM) and electrophoretic mobility experiments.
Single, double and triple coatings [6] were performed by alternating positive and negative shells of nanoparticles. The strength of the coatings was checked by removing the excess of nanoparticles and isolating the stable core-shell microstructures. This step was developed by centrifugalizing the dispersions and redispersing the coated particles into pure solvent. These core-shell structures were visualized by T.E.M.