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

The application of the miniemulsion polymerization technique to the encapsu lation of titanium dioxide (TiO2) inside polystyrene latex particles was in vestigated. Complete encapsulation, meaning all of the polystyrene encapsul ating all of the TiO2 in the colloidal particles, was not achieved. The mos t successful encapsulations were only achieved when the TiO2 particles, eit her hydrophilic or hydrophobic, were well dispersed in the styrene monomer prior to formation and polymerization of the miniemulsions. The TiO2 disper sions in styrene were prepared by sonification of the TiO2 in the presence of an adsorbing steric stabilizer OLOA 370 (polybutene-succinimide pentamin e). Miniemulsions were prepared by dispersing the monomer phase (also conta ining hexadecane as a costabilizer and polystyrene to enhance the nucleatio n 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 separ ations) and particle size. The maximum encapsulation efficiencies (83% TiO2 and 73% polystyrene) were achieved using hydrophilic TiO2 particles stabil ized 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 part icle increased with the largest particle size (209 nm) containing an estima ted 22 TiO2 particles. (C) 2000 John Wiley & Sons, Inc.