Stabilization of Water/Oil/Water Multiple Emulsion with Hypertonic Inner Aqueous Phase.

Water/oil/water emulsion (w/o/w emulsion) was prepared with liquid paraffin, a hydrophobic surfactant (Span 80) and a hydrophilic surfactant (Tween 20) by a two-step emulsification procedure. The percentage of solute entrapped in the inner aqueous phase and the viscosity of the emulsion system increased with an increase in the concentration of solute (glucose of sodium chloride) initially added to the inner phase of the emulsion. The oil membrane of the w/o/w emulsion, which entrapped the hypertonic inner aqueous phase, was thick, and the release of the solute from the emulsion was slow. The viscosity of w/o/w emulsion entrapping a hypertonic inner aqueous phase was large, and consequently, separation of the aqueous phase was delayed. A decrease in the encapsulation efficiency of w/o/w emulsion during storage was considered to be the result of a rupture of the oil membrane. Destruction of the w/o/w emulsion followed first-order kinetics. The rate constant of destruction of w/o/w emulsion at room temperature could be predicted by meauring the destruction rate at a higher storage temperature.