NOVEL PREPARATION METHODS FOR HIGHLY CONCENTRATED WATER-IN-OIL EMULSIONS

Kinetically stable water-in-oil (W/O) high-internal-phase-volume-ratio emulsions with gel-like appear ance have been formed in water/hydrogenated non-ionic surfactant/oil systems. Their visual aspect varies from transparent to translucent or white depending on composition variables and temperature. Systematic studies undertaken to characterize these emulsions, referred to as gel emulsions, have revealed that they form above the hydrophilic-lipophilic balance (HLB) temperature of the corresponding ternary system. They consist of two isotropic liquid phases; the dispersed phase is composed of aqueous droplets and the continuous phase is a W/O microemulsion. These emulsions can be prepared by gradual addition of the internal phase to the external phase while stirling, the most common method for preparing highly concentrated emulsions. In the ternary systems water/non-ionic surfactant/hydrocarbon we found two new procedures for preparing gel emulsions. (a) Mixing of the three components, at their final composition, with vigorous stirring, can lead, at the appropriate temperature, to gel emulsion formation. (b) Increasing the temperature of an isotropic phase, the composition of which is that of the final emulsion. These methods of preparation have been rationalized in terms of the evolution of system properties during the process.