Improvement of the stability of water-in-oil-in-water multiple emulsions by the addition of surfactants in the internal aqueous phase of the emulsions

Abstract

In order to improve the stability of w/o/w emulsions, an attempt was made to elucidate the influence of addition of hydrophilic surfactants into the internal aqueous compartment of the emulsion, on the breakdown of the suspending vesicular globules of w/o/w emulsion, the changes in diameter of the internal aqueous compartments and of the suspending vesicular globules of w/o/w emulsion, as compared with emulsions without additives and with addition of sodium chloride. It was also attempted to measure the effect of addition of hydrophilic surfactant to the three different phases on the stability of w/o/w emulsions. The stability of diluted w/o/w emulsions with a large difference in osmolarity between the internal aqueous compartments and the external aqueous phase was also tested, w/o/w emulsions were prepared by the two-step emulsification procedure. New coccine was employed as a marker to check the yield of formation and the breakdown of the w/o/w emulsions. Sodium octanesulfonate was used as an additive in the internal aqueous compartment of the w/o/w emulsions as well as sodium chloride. Polyoxyethylene (20) sorbitan monooleate was used as an additive to the three different phases of the emulsions. The stability of w/o/w emulsions, as determined by coalescence of internal aqueous compartments and their increase in size by the influx of water to the internal aqueous compartment from the external aqueous phase, was improved by the addition of hydrophilic surfactant in the internal aqueous compartments of the emulsions. This was observed even under the condition of a large difference in osmolarity between the internal aqueous compartments and the external aqueous phase, and was affected by the concentration of hydrophilic surfactant. The addition of sodium chloride to the internal aqueous compartments and of hydrophilic surfactant to the external aqueous phase did not improve the stability of w/o/w emulsions. Only the addition of hydrophilic surfactant into the internal aqueous compartments was demonstrated to inhibit both coalescence of internal aqueous compartments and influx of water to the internal aqueous compartment from the external aqueous phase. On the other hand, the addition of hydrophilic surfactant into the oil phase was observed not to inhibit coalescence but water influx.