EMULSION PHASE INVERSION 195 Z t•' IOO I I I I TRITON X-IO0- ARLACEL 83 i I I I 0 20 40 60 80 I00 Xh, WT.% TRITONX-IO0 INITIALLY INAQ. PHASE Figure 7. Effect of initial surfactant location on q, (mineral oil stabilized with Triton X-100 - Arlacel g3 at HLB g) Figure 7 shows the results obtained with mineral oil emulsions stabilized with Triton X-100 and Arlacel 83 at HLB 8. This S-shaped curve also indicates strong dependency of ½ on the initial surfactant location. Again, the trend to form an O/W emulsion with an increase of the hydrophilic surfactant in the aqueous phase is unmistakable. When a hydrophilic surfactant, such as Triton X-100, is mixed into mineral oil containing a lipophilic surfactant, Arlacel 80, it is reasonable to expect that a large portion of Triton X-100 will be solubilized in the Arlacel 80 micelies. When water is added to this mixture to form an emulsion, a substantial part of Triton X-100 and a small portion of Arlacel 83 will eventually migrate to the aqueous phase to establish an equilibrium. Con- ccivably, the transport process involved here may be relatively slow and,

196 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS [ ' ' ' ' 4 z TRITON x-moo- ARLACEL 83 80 IMMEDIATE '70 0 20 40 60 80 I00 Xh, Vl/I% TRITON X-IOOINITIALLY IN AQ. PHASE Figure 8. Effect of delayed emulsification on • (mineral oil stabilized with Triton X-100 - Arlacel 83 at HLB 8) hence, the effect of the initial surfactant location becomes important in determining the type of emulsion formed. To decide if the hypothesis presented here is a reasonable one, another series of experiments was carried out to determine the effect of time on 4. In Fig. 8, the solid line represents the usual • values obtained with emulsions stabilized with Triton X-100 and Arlacel 83 at HLB 8. However, unlike the previous experiments, the emulsions were prepared in half-gallon jars instead of the emulsification vessel. The second set of emulsions, represented by a broken line, was also prepared in half-gallon jars. Instead of emulsifying the oil immediately after the oil phase was placed on the aqueous phase, the system was left