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Preparation conditions

Oil phase:

Divinylbenzene (monomer)

Water phase:

Water containing 0.2 wt.% SDS

Stabilizer:

Polyvinyl alcohol

Catalyst:

Benzoylperoxide

Membrane:

Hydrophilic SPG; Dp=1.36 [im

Temperature:

Room temperature

Figure 14. Microphotograph of polydivinylbenzene microspheres (Courtesy of Nakashima and Shimizu^®)

3.3.3. Preparation of Uniform Multiple Emulsions

Multiple emulsion is an emulsion within an emulsion. Water-in-Oil-in-Water (W/O/W) type multiple emulsions are oil-in-water emulsions in which the dispersed oil drops in turn contain dispersed aqueous droplets. These systems were observed as long ago as 1890 (46), but there has been increased interest recently in the use of W/O emulsion in such diverse fields as the food emulsions(47-51), waste water treatment (52), immobilization of enzymes (53) and treatment of drug overdosage (54). It should be noted that the stability of the multiple emulsion depends greatly on the type and concentration of the surfactant. As for the structural characteristics, the single compartment globules of the W/O/W emulsions are morphologically similar to those of the one-lamellar liposome systems, although the size and shape are somewhat different. Multiple emulsion so far has been generally produced by two-step process.

Figure 15 shows a schematic diagram for the preparation of double emulsion by using a double SPG membrane module. The sizes of oil (water) droplet and inner water (oil) phase can be varied by changing Dp of the inner and outer SPG membranes, respectively.

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Figure 15. Schematic diagram of the preparation of double emulsion.

Figure 16 exhibits an example of W/O/W multiple emulsion prepared by the double SPG membrane module. First, the W/O emulsion was prepared by dispersing a water phase into a vegetable oil phase using lipophilic nonionic surfactants and then dispersing this W/O emulsion into a water phase containing a hydrophilic nonionic surfactant.

Furthermore, the W/O/W multiple emulsion can be utilized for preparing the monodispersed colloidal inorganic particles via interfacial reactions. Figure 17 displays a typical micrograph of precipitated microspheres. A lwt. % sodium alginate solution was dispersed in n-hexane solution containing 0.25 wt. % Span-85 and 0.25 wt. % of Tween 85 to prepare a primary emulsion. The W/O emulsion, thus obtained, was dispersed in 15 wt.% CaCl2 solution (secondary emulsification).

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