Spontaneous formation of highly concentrated water-in-oil emulsions (gel-emulsions)

Water-in-oil-type gel-emulsions (or highly concentrated emulsions) are spontaneously formed from oil-swollen micellar solutions or oil-in-water (O/W) microemulsions in a water/tetraoxyethylene dodecyl ether/oil system with an abrupt increase in temperature. The phase change occurs from water-continuous microemulsion to water-in-oil (W/O) gel emulsion via a lamellar liquid crystal and a bicontinuous surfactant phase (L(3) phase). Hence, the spontaneous curvature of the surfactant layer is continuously changed with temperature change because the gel-emulsion consists of a reverse micellar solution and an excess water phase. In a narrow temperature range above the single L(3)-phase region, there is a two-phase region consisting of L(3) and an excess water phase (W) in which emulsions are extremely unstable. The electroconductivity curve as a function of temperature monotonically decreases with increasing temperature when the final temperature is high and the temperature change is fast. If the temperature change is very slow, the electroconductivity has a maximum at the temperature where the L(3) + W region is found because excess water is separated. In this case, the water droplet size in the final concentrated emulsion is very large. Therefore, it is important to change the temperature quickly to form fine gel-emulsions.