EFFECTS OF HUMECTANTS ON EMULSION OCCLUSIVITY 265 Table VI Occlusivity of Ternary Mixtures Prepared From Mineral Oil and Ester Surfactant Parameters HLB 8.5 9.5 10.5 11.5 Water NaL (10%) Nature I.O. I.O. I.O. N.I.O. Occlusivity (%) 29 + 3 36 +-- 2 20 + 2 0 I.O. (%) 3 1.8--6.9 2.4--•5.2 0 Nature I.O. I.O. I.O. N.I.O. Occlusivity (%) 30 + 3 65 + 3 32 ñ 1 12 ñ 3 I.O. (%) 2.5 1.5--•6.8 2.4--5.7 0 Same legend as Table V. An emulsion prepared from P.H.S. with ester linkage surfactant of HLB 9.25 left a continuous residual "film," whereas the emulsion prepared from HLB 11.5 surfactant left a porous film (Figures 4a and 4b). The same phenomena were also observed with ternary mixtures (Figures 4c and 4d). An emulsion prepared from mineral oil with ester surfactant of HLB 9.5 formed a more continuous film than one prepared with HLB 11.5 surfactant (Figures 5a and 5b). Comparable phenomena occurred with ternary mixtures prepared with HLB 9.5 and 11.5 surfactant (Figures 5c and 5d). DISCUSSION The occlusivity of emulsions has been described as dependent on the nature of their non-volatile components (4,14-16). Our previous results (8,10) showed that the oc- clusivity of emulsions depended mainly on their capacity to form an isotropic oily phase following dehydration on the surface of application. The HLB value of surfactant used to form the emulsion played a major role in determining the emulsion's occlusive properties. The physicochemical properties we have analyzed provide an explanation for the modification of the occlusive properties of emulsions by the presence of humectants. ISOTROPIC OILY PHASE FORMATION CAPACITY Emulsions having the highest isotropic oily phase formation capacity offered the greatest occlusivity, e.g., emulsions prepared from perhydrosqualene with ester surfactant of HLB 9.25. Emulsions having no isotropic oily phase formation capacity showed a weaker occlusivity, e.g., emulsions prepared from perhydrosqualene with ester surfac- tant of HLB 11.5. In most cases, the humectants diminished the occlusivity of emulsions. This can be explained by their ability to decrease isotropic oily phase formation capacity, e.g., emulsions containing sodium lactate which were prepared from P.H.S. with ester surfactant of HLB 8.5 or from mineral oil with ether surfactant of HLB 9.5. In exceptional cases, the presence of humectants enhanced the occlusivity of emulsions. This phenomenon corresponds well to their tendency to increase the isotropic oily phase formation capacity of emulsions, e.g., emulsions prepared from mineral oil using ester surfactant of HLB 9.5.

266 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS . ..-:,.-::.,.. :...:- " .. • ,,- .. ,•.:•' :..'•:.. ::...•- ,. •, -, s,• %. -, • - • -.• •-•..• ',? .,.... ,.--.• •.•.'•% ,-- ... ' •_-•5• '• '• - • • '- - •-' , •.•' ..• ...., .... ,•.,-.• .•.-.•'• Figure 4. Microscopic views of emulsions and ternary mixtures prepared from perhydrosqualene and ester surfactants of HLB 9.25 (a,c)and 11.5 (b,d). VISCOSITY Although increased viscosity was supposed to enhance the occlusive properties of prod- ucts (17), our experimental data showed that it did not have any effect. For example, in the case of non-volatile parts of emulsions prepared from perhydrosqualene and ester surfactant of HLB 8.5, sodium lactate increased their viscosity whereas it decreased their occlusivity. Similar results occurred in other cases. CONDUCTIVITY It was thought that products having greater conductivity would facilitate the diffusion of water and thereby be less occlusive. However, according to our results, there did not exist any relationship between the conductivity and the occlusivity of the product. In the light of above analysis, it is now clear that isotropic oily phase formation capacity of emulsions is one of the major factors in determining their occlusivity. These findings