PREPARATION AND APPLICATION OF INORGANIC MICROCAPSULES

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In the present study, we applied the carrier-mediated penetration of ions to the preparation of inorganic microcapsules with the interfacial reaction method originally proposed by Nakahara. Two kinds of ion-carrier, cation and anion exchanger, were employed in organic solvents. The effects of preparation conditions on the rates of encapsulation and the surface state of inorganic capsules were examined to establish the reaction mechanism and to find the optimum preparation conditions. Most of the experiments were carried out for calcium silicate capsules. Some of the silicate capsules were prepared by using the salts of transition metals.The rates of encapsulation were affected by the factors which controlled the penetration rates of ionic species through oil phase. The increase in the carrier concentration and the dispersion rate of W/O emulsion into outer aqueous phase solution accelerated the encapsulation, whereas the surfactant concentration and oil-phase viscosity showed the reverse effects. The encapsulation rates increased by raising the concentration of inorganic compounds dissolved in both aqueous solutions. Based on these findings, the rate-controlling step of encapsulation were suspected to be the penetration through oil-phase film at the outer periphery of W/O emulsion drops. With the progress of shell formation, however, the transfer through inorganic shell may control the encapsulation processes. The state of capsulation was also affected considerably by preparing conditions. The increase of surfactant and salt concentrations were especially effective to improve the formation state of spherical capsules. The experimental methods to prepare the capsules made of different metals were proposed.