ABSTRACT

I. INTRODUCTION An emulsion is an opaque, heterogeneous system of two or more immiscible liquids ("oil" and "water") generally stabilized by a third component, surfactant or other emulsifiers, where one of the liquids is dispersed as droplets of microscopic or colloidal size in the other [1]. High internal-phase volumeratio or highly concentrated emulsions are designed with the volume fraction of a dispersed phase, which exceeds Ostwald's critical volume fraction (0.74) for the closest packing spheres [2-4]. Due to their high viscosity and gellike consistency, they are also called gel emulsions. The gel emulsions have received particular interest for specific applications as formulations such as gelled fuels, emulsion explosives, cosmetics, pharmaceuticals, etc. and novel reaction media for polymerization reactions [5,6]. Highly concentrated emulsions have been studied earlier, usually consisting of two isotopic liquid phases, which are formed in either water-or oil-rich regions of watersurfactant-oil systems [7-16]. In the oil-rich region oil droplets are dispersed in a small amount of aqueous micellar solution phase (O(W or 0/W m emulsions), whereas in the water rich-region, water droplets are dispersed in the oil-swollen reverse micellar solutions (W/0 or W/Om emulsions). In both cases of emulsions, since a large amount of internal phase (maximum up to 99 + %) is dispersed in a very small amount of continuous phase, each droplet touches closely to another and cannot move, and hence they are often very viscous. However, since the droplets are covered by a flexible surfactant monolayer, these emulsions are rather fragile against coalescence, although the stability of W /0-type concentrated emulsions increases upon

addition of inorganic salt. Other types of emulsions are also known although their structures are not completely known [17,18].