Introduction

Emulsification has been used in various industrial applications for processing food, cosmetics, medicine, paints, etc. Numerous studies have been reported on the preparation of both Oil-in- Water(0/W) and Water-in-0il(W/0) emulsions (1-7). Also, many emulsification equipments such as colloid mill, homogenizer, ultrasonication etc. are being used in various industrial fields (8). However, their emulsification conditions cannot be precisely controlled and the emulsion droplets are polydispersed. According to the DLVO theory (9), the monodispersity of emulsion droplets is necessary for forming a stable dispersion against aggregation. Therefore, a new emulsification technology for producing monodispersed emulsions became attractive. Incidentally, in many applications the monodispersity in droplet size can be regarded as a plus.

Recently, Nakashima and Shimizu developed a new type of porous glass, the pores of which are uniformly controlled in size, synthesized from Ca0-Al203-B203-Si02 type glass, and made from "Shirasu" which is available as volcanic ashes in the southern part of Kyushu, Japan. This was named Shirasu-Porous-Glass (SPG) (10,11). In 1988, they proposed a method for the preparation of emulsions using SPG and referred to as "SPG Membrane emulsification" (12). The monodispersed oil droplets were simply formed by pressing an oil into a water phase through the uniformly controlled pores of SPG membrane. Because of its simplicity and less energy consumption, this technique became attractive. In this chapter, the feature and application of this new membrane emulsification technique will be explained, specifically highlighting the methodology, on the basis of a pioneering work of Nakashima and Shimizu and the author's investigations (13-15). Applications of microporous glass membranes in emulsification to produce monodispersed droplets, production of uniform silica hydrogel particles, preparation of uniform polymer microspheres, preparation of uniform multiple emulsions, and ozonation of liquids are discussed.

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