Encapsulation of inorganic particles via miniemulsion polymerization

The encapsulation of TiO2 particles via miniemulsion polymerization is stro ngly dependent on the size and stability of the inorganic particles in the monomer medium in which they are initially dispersed. It was found from XPS and FT-IR studies that both the hydrophilic and hydrophobic TiO2 particles , which were studied, have hydroxyl groups present on their surfaces, which can strongly interact with the amine end-groups of the polymeric stabilize r, OLOA370 (polybutene-succinimide diethyl triamine). It was found from the dispersion and adsorption studies that the amount of OLOA370 retained on t he TiO2 particles is strongly dependent on the area exposed by the sonifica tion that is applied to break up the aggregates in the dispersion process. The TiO2 dispersions in styrene monomer were themselves dispersed as miniem ulsion droplets and subsequently polymerized. It was concluded from the den sity gradient column (DGC) analysis of the latexes obtained from the encaps ulation polymerizations, that the stability of the inorganic particles in t he monomer, as well as their particle size, significantly influence the enc apsulation efficiencies. The use of the hydrophilic titanium dioxide partic les in combination with the stabilizer, OLOA370, resulted in a good dispers ibility, dispersion stability, and small TiO2 particle size. This lead to b etter encapsulation efficiencies compared to the hydrophobic particles. The poorer results obtained with the hydrophobic TiO2 particles were attribute d to their larger particle size, which resulted from the reduced adsorption of the OLOA370. Fewer hydroxyls and the presence of the trimethoxy octyl s ilane (TMOS) groups, which themselves are unable to provide sufficient ster ic stability, are proposed to explain these findings.