Toru Tagawa

Syntheses of composite polystyrene latices with silica particles in the core

Abstract A study of the synthesis of composite polystyrene latices with silica particles in the core has been performed under various conditions. It was apparent that the dense adsorption layer of hydroxyl propyl cellulose (HPC), which was formed on the silica particles at the lower critical solution temperature, plays a part in the preparation of the composite. When the bare particles of silica were used in the seeded emulsion polymerization, there was no tendency for encapsulation of the silica particles and, indeed, new polymer particles were formed in the aqueous phase. On the other hand, encapsulation of the seed particles proceeded preferentially when the HPC-coated silica particles were used as the seed and fairly monodisperse composite latices including silica particles were prepared. Furthermore, in the high concentration runs of the SDS, a new type of composite with a raspberry shape was generated with a high product yield. It is assumed that nucleation of new polymer particles would occur above the critical micelle concentration of the surfactant and that one portion of the new polymer particles would coagulate heterogeneously with the HPC-coated silica particles after some period of the seeded polymerization.

Polymer-oil microemulsions

Thermodynamically stable microemulsions are formed in a water(brine)/ionic surfactant/cosurfactant/polymer-oil(silicon oil having an NH2 group) system. The effect of added salt on the formation of microemulsions is remarkable. The cosurfactant/ionic surfactant ratio to give the maximum solubilization decreases with the increase in salinity. The minimum concentration of surfactant (ionic surfactant + cosurfactant) to make equal amounts of water and polymer oil a single phase is decreased upon addition of salt. The salt also has the effect of destroying lamellar liquid crystal which turns into isotropic microemulsions. The electrical conductivity data show that water-continuous, oil-continuous, and bicontinuous microemulsions are formed in this polymer-oil system. Microemulsions were not found in a polydimethylsiloxane system at a water/oil ratio of unity. Hence, the NH2 group in silicone oil is important to form microemulsions. The hydrophilic groups of silicone oils may penetrate to the palisade layers of ionic surfactant and cosurfactant to stabilize microemulsions.