Ceramic micro-particles synthesised using emulsion and sol-gel technology:: An investigation into the controlled release of encapsulants and the tailoring of micro-particle size

Controlled release technologies have many applications in such diverse fields as the pharmaceutical, agricultural, cosmetic and food industries, where tailored release rates and protection of the active molecule for delivery at a specific site or time are advantageous. Silica microspheres, with controlled diameters of 10-50 mu m and containing Orange II dye as a model encapsulant, have been synthesised by combining water-in-oil (w/o) emulsion technology with sol-gel chemistry. The average particle size may be controlled by the microemulsion parameters, including the surfactant and solvent concentrations, and by the sot-get processing parameters, particularly water-to-silicon alkoxide ratio, pH, temperature, ageing and mixing conditions. Physical properties of the SiO2 microspheres, which modulate the release rates of the encapsulated molecule (including pore size and tortuosity), are also controlled by the sol-gel process parameters. The effect of synthesis parameters, including surfactant concentration, sol-gel solution pH and drying temperature, on the morphology of the SiO2 microspheres produced will be discussed. The effect of such parameters on the corresponding release rates of the model encapsulants will also be presented.