162 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS oil/surfactant (O/S) ratio was the greatest. For example with perhydrosqualen occlusivity at HLB = 8.5 was 47 _+ 5% for O/S ratio -- 3 and 30 _+ 2% for O/S ratio = 2. The variations were in the same order with mineral oil, sweet almond oil and Miglyol 812 © at HLB values of 8.5 and 9.25. At HLB values of 11.75 this phenomena was not observable. COMPARISON OF OCCLUSIVITY OF OIL-SURFACTANT MIXTURES AND CORRESPONDING EMULSIONS Comparison of the occlusive capacity of oil-surfactant binary mixtures with emulsions containing the same oil/surfactant ratio at different HLB values showed that there exists an HLB value for which the occlusivity was maximum (Fig. 4). When comparing 100 _ © P.H.S. o MINERAL OIL ß SWEET ALMOND OIL IGLYOL 81 2 ,,/ H.L.e. 8,5 9,25 10,5 11,75 Figure 4. Occlusivity of oil/surfactant (Montane 80 © and Montanox 80 ©) binary mixtures: 15/5 at various HLB values corresponding to the water/oil/surfactant emulsions: 80/15/5 without water. occlusivity of binary mixtures and the corresponding emulsions (Fig. 5) a strong correlation was found (r = 0.95). Analysis of the diagrams constructed with the same materials for various HLB values in the zones for which the water content is low showed that for each oil a maximum isotropic oil phase formation was observed for a given HLB (Fig. 6 and 7). The facility of the formation of isotropic oil phase was related to the surface area occupied by this phase in the diagram. So it was shown that for each oil, the HLB value at which the occlusivity of the emulsions was the greatest corresponded to the maximal surface area of isotropic oil phase on the diagrams. This particular HLB is identical to that for which occlusivity of the corresponding emulsions is greatest (Fig. 8, 9, 10, 11).

OCCLUSIVITY OF AQUEOUS EMULSIONS 163 zlO0 o • 90 • 80 7O o 6O o5o 4O 3O 20 10 r= 0,94 I ! ! I I ! 10 20 30 40 0 60 70 0 90 1•)0 %0 OF BINARY MIXTURES (oil_ surfactant) Figure 5. Correlation between the occlusivity of emulsions and that of binary mixtures oil/surfactant (Montane 80 © and Montanox 80©). DISCUSSION Once an emulsion is applied to the surface of the skin, its structure modifies with time because the water evaporates rapidly and only a residue containing principally the non-volatile materials persists (10). Comparable phenomena occur in our experimental conditions on the surface of the gelatin film. Immediately after application of the emulsion, the water starts to evaporate and coalescence of oil droplets occurred forming finally a continuous occlusive film. The water evaporation kinetics measured under the same conditions of temperature and RH on an inert support, showed that the totality of water was evaporated in 10-15 minutes according to the nature of the oil or surfactants used and HLB values of the emulsions. The residual quantity of water which persists in the mixture was approximately 5 to 10%. The qualitative composition of this residue is comparable to that of an isotropic oil phase. As the results of occlusivity measurements carried out on the mixture