Encapsulation of inorganic particles via miniemulsion polymerization. III. Characterization of encapsulation

Abstract

The application of the miniemulsion polymerization technique to the encapsulation of titanium dioxide (TiO2) inside polystyrene latex particles was investigated. Complete encapsulation, meaning all of the polystyrene encapsulating all of the TiO2 in the colloidal particles, was not achieved. The most successful encapsulations were only achieved when the TiO2 particles, either hydrophilic or hydrophobic, were well dispersed in the styrene monomer prior to formation and polymerization of the miniemulsions. The TiO2 dispersions in styrene were prepared by sonification of the TiO2 in the presence of an adsorbing steric stabilizer OLOA 370 (polybutene–succinimide pentamine). Miniemulsions were prepared by dispersing the monomer phase (also containing hexadecane as a costabilizer and polystyrene to enhance the nucleation of the droplets) in water using sodium lauryl sulfate as surfactant. The latexes resulting from the subsequent polymerizations were characterized in terms of the encapsulation efficiencies (via density gradient column separations) and particle size. The maximum encapsulation efficiencies (83% TiO2 and 73% polystyrene) were achieved using hydrophilic TiO2 particles stabilized with 1.0 wt % OLOA 370. As the density of the particles collected from the density gradient column increased from zone to zone, both the average particle size and number of the TiO2 particles contained in each latex particle increased with the largest particle size (209 nm) containing an estimated 22 TiO2 particles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4441–4450, 2000