THE INFLUENCE OF COEMULSIFIER TYPE ON THE STABILITY OF OIL-IN-WATER EMULSIONS

Oil-in-water emulsions containing ethoxylated non-ionic surfactants may undergo a phase inversion to water-in-oil emulsions on heating. This temperature-induced phase inversion is utilized in the so-called phase inversion temperature (PIT) method for the preparation of finely dispersed bluish oil-in-water emulsions. PIT emulsions with polar oil components were prepared by adding mixtures of fatty alcohol ethoxylates with or without the coemulsifier glyceryl monostearate. In the phase inversion temperature range, microemulsion or liquid crystalline phases are formed depending on the type of emulsifier mixture used. The formation of a bicontinuous or lamellar structure is essential in order to obtain finely dispersed oil-in-water emulsions. In both phases the hydrophilic-lipophilic properties are balanced, which results in minimum interfacial tensions between oil and water phases. Fine dispersity, however, is not the only criterion for stable oil-in-water emulsions. Studies of different parameters of the emulsions give hints to the stabilization mechanism of the emulsifier/coemulsifier system. According to these results, low viscous PIT emulsions exhibit long-term storage stability, if the oil droplets are shielded against coalescence by a lamellar gel phase, which is imparted by the coemulsifier glyceryl monostearate.