STABILITY OF MULTIPLE EMULSIONS 221 Table IV Marker Retention in Multiple Emulsion, HLB = 6, 10 (n = 3) Mean % marker retained Time (days) a b c d e 1 98 96.8 99 100 96.6 7 78.6 68.6 94.4 94.3 62.7 14 56.7 49.6 87.9 84.2 42.9 28 38.1 35.8 78.2 71.3 31.4 See Table III for description of formulations. III). On the other hand, balancing osmotic pressure seems to result in a small increase in stability in the 6, 10 emulsions. At the higher ionic strength there is no statistically significant difference (b and e, Table IV) at the lower ionic strength, there is a statis- tical difference (p 0.05) in the values at i4 and 28 days (c and d, Table IV). An important conclusion based on these studies is that polyporphyre retention is a valid measure of oil film integrity since its migration by diffusion is insignificant. This is borne out by the high degree of retention in some of the emulsions. Thus, despite the existence of a concentration gradient, only 1% of the marker was transferred from the W 1 to the W2 phase is emulsions with an ionic strength of 0.01 and balanced osmotic pressure during a 27-day period (emulsion c, Table III). Furthermore, comparison of retention data for emulsions a and b in Tables III and IV shows that a difference in marker concentration has little effect on retention, suggesting that the presence of polymeric marker is not a significant determinant of emulsion properties. APPLICATION TO A TYPICAL MULTIPLE EMULSION SYSTEM Figure 3 illustrates marker retention (determined by Method 1) in duplicate emulsions (HLB = 4.3, 6) over a 51-day period. Reproducibility was relatively good. Based on linearity of the plot of the logarithm of marker retention versus time, oil film rupture in these systems is an apparent first-order process. Further experiments on the relationship between HLB and stability over time are in progress and will be reported subsequently. ACKNOWLEDGEMENTS The authors are grateful for fellowship support provided through a Society of Cosmetic Chemists Education Institution Award and project support from the Kelco Division of Merck and Company. REFERENCES (1) E. Sheppard and N. Tcheurekdjian, Comments on multiple phase emulsions, J. Colloid Interface Sci., 62, 564-565 (1977). (2) S. Matsumoto, Y. Kita, and D. Yonezawa, An attempt at preparing water-in-oil-in-water multiple phase emulsions, J. Colloid Interface Sd., 57, 353-361 (1976).

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