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

Oil-in-water emulsions containing ethoxylated non-ionic surfactants ma y undergo a phase inversion to water-in-oil emulsions on heating. This temperature-induced phase inversion is utilized in the so-called phas e inversion temperature (PIT) method for the preparation of finely dis persed bluish oil-in-water emulsions. PIT emulsions with polar oil com ponents were prepared by adding mixtures of fatty alcohol ethoxylates with or without the coemulsifier glyceryl monostearate. In the phase i nversion temperature range, microemulsion or liquid crystalline phases are formed depending on the type of emulsifier mixture used. The form ation of a bicontinuous or lamellar structure is essential in order to obtain finely dispersed oil-in-water emulsions. In both phases the hy drophilic-lipophilic properties are balanced, which results in minimum interfacial tensions between oil and water phases. Fine dispersity, h owever, is not the only criterion for stable oil-in-water emulsions. S tudies of different parameters of the emulsions give hints to the stab ilization mechanism of the emulsifier/coemulsifier system. According t o these results, low viscous PIT emulsions exhibit long-term storage s tability, if the oil droplets are shielded against coalescence by a la mellar gel phase, which is imparted by the coemulsifier glyceryl monos tearate.