Sol–gel microencapsulation of hydrophilic active compounds from the modified silicon alkoxides: The control of pore and particle size

The present paper has demonstrated one-pot preparation of the spherical silica microcapsules containing hydrophilic active compounds using a water-in-oil microemulsion process from the modified silicon alkoxides with 3-aminopropyl triethoxysilane (APTES) as a gelling agent. The H2O-to-TEOS molar ratio in the preparation of the encapsulation precursors played an important role on controlling the morphology and pore size of the microcapsules. The spherical microcapsules were obtained in the range of H2O/Si = 1.5–1.7. Outside this range no spherical microcapsules was observed because the precursors were not miscible with hydrophilic active compounds below the range and gelled too fast above the range. The average particle sizes of the microcapsules were controllable in the range of sub-micrometers to several tens of micrometers by adjusting agitation speeds, and the properties of the precursors. The pore size of the microcapsules can be also tuned by changing the H2O-to-TEOS molar ratio in the preparation of the encapsulation precursors.