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* Monodispersity ratio, U=Di/D2, where Di and D2 are weight- and number-mean diameters of water droplets, respectively.

$ Critical pressure for the penetration of sodium silicate solution or water through the SPG filter.

Figure 13. Scanning electron micrograph of silica microsphere(Courtesy of Nakashima and Shimizu^®)

3.3.2. Preparation of Uniform Polymer Microspheres

Spherical and monodispersed polymer latices have attracted a great deal of attention because it is widely used as a model for the study of colloidal stability in aqueous and nonaqueous media (38-45). Of course, because of its high specific surface area, these polymer microspheres may have the applications similar to silica gel cited in a previous section. Furthermore, from its unique feature of polymer microsphere, the flavor and aroma compounds and nutrients are not only adsorbed on the particle surface but also can be incorporated in the particles by encapsulation. Therefore, their efficiency will be maintained for a longer time.

Figure 14 shows the micrograph of polydivinyl benzene microspheres (PBM). PBM was formed in monodispersed oil droplets dispersed in water phase (O/W emulsion). This method utilized a suspension polymerization and can be applied to other oil-soluble monomers. On the contrary, in the case of water-soluble monomer such as acrylamide, one can prepare water-soluble polymer microspheres as water droplets dispersed in an oil phase by preparing monodispersed W/O emulsion. Such microspheres can also be applied to the preparation of microcapsule delivery system for flavor, aroma and nutrient.

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