(247b) Preparation of Uniform Microcapsules with Silicone Oil as Continuous Phase in a Microchannel Device

Microcapsules have very interesting characteristics and the technology of microcapsulation has been used in various fields such as medicine, agriculture, foods and the chemical industry. Solvent evaporation method is widely used in preparation of microcapsules. This technique neither requires special equipments nor phase separation-inducing agents. Controlled particle sizes in the nanometer to micrometer range can be achieved. But careful selection of encapsulation conditions and materials is needed to yield high encapsulation efficiencies. So far, most researchers use dichloromethane or chloroform as the evaporated solvent. As a result, only polymers which are soluble in the chlorohydrocarbons mentioned above can be used as a shell material. Because species of shell material greatly influence the mass transfer performance of microcapsules, it will be very helpful to produce perfect microcapsules if more shell materials can be used. Poly(dimethylsilicane) (PDMS), also named silicone oil when it is in liquid state. Silicone oil has very good chemical stability, thermal stability, and physiological safety. The solubility of polar compounds or macromolecular compounds in silicone oil is often very small. This paper presents an improved solvent evaporation method with silicone oil as the continuous phase to make more polymer solvents available. A T-shaped microchannel device was used to produce emulsions instead of mechanical stirring to prepare the mono-dispersed microcapsules. Lower evaporation temperature and shorter evaporation time were required in the new process. Uniform polyacrylonitrile (PAN) microcapsules containing Aliquat 336 (ALQ) have been successfully prepared. N,N-dimethylformamide (DMF), a widely used solvent with very good dissolution ability but lower evaporation ability, was applied as the polymer solvent. The prepared microcapsules have rough surfaces and homogeneously internal structures. Microcapsules' mean diameters and loading ratio were influenced by the composition of polymer solution and evaporation temperature. By changing the two-phase flow rate, the mean size of microcapsules can be easily controlled. When more ALQ was added in polymer solution, the loading ratio of microcapsules increased. The mass transfer performance and stability were determined by extraction of Cr2O72- ions from its aqueous solution. The mass transfer rate are enough fast. After three times of repeated extraction and stripping, the microcapsules kept almost the same extraction ability, which indicated that the microcapsules have very good stability.