The encapsulation of silica particles was carried out by emulsion polymerization of isoprene in aqueous solution.
Precipitated silica Zeosil 175 with a particle size of 0.05㎛, synthetic isoprene, cetyltrimethylammonium bromide(CTAB), and potassium persulfate(KPS) were used.
In order to encapsulate $SiO_2$ particles uniformly, polymerization should be occurred on the surface of $SiO_2$ particles, and suppressed in the bulk phase as much as possible. These will be attained both by increasing the adsorption of surfactants to enhance the portion of monomer solubilized into adsorbed layers of surfactant, and by localizing initiators on the surface of $SiO_2$ particles.
To achieve both conditions effectively, the adsorption behaviors and the polymer yields were investigated under various conditions.
The cationic surfactant adsorbed onto $SiO_2$ particles formed an oil-soluble salt with KPS, which was insoluble in water.
The deposition of the salt onto $SiO_2$ particles enhanced the adsorption amount of surfactant considerably, and induced the increase of solubilization of isoprene into the adsorbed layers of surfactant.
Under CMC, the polymerization of isoprene solubilized into adsorberd layers was found possible to encapsulate $SiO_2$ particles with little formation of the latex polymer.
As a result, the yield of capsulating polymer was upto 70 percent at the pH of 12.3.
Electron micrographs and IR spectra of the polyisoprene-encapsulated $SiO_2$ showed that silica particles were uniformly encapsulated with the resulting polymer.
