158 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS In this work an attempt has been made to explain some aspects of occlusivity of emulsions using a model of highly hydrated gelatin (7). Measurements of water loss were made with various emulsions prepared via ternary phase diagrams. Some of the experimental objectives were: 1) to assess the importance of the concentration of constituents of the emulsions 2) to evaluate the role of the nature of surfactants and oils and 3) to determine the role of the physical structure of emulsions made by the same procedure and of their oily phase. EXPERIMENTAL MATERIALS Four oils of different polarity were chosen. Their classification according to the dielectric constant was as follows: Perhydrosqualen (P.H.S.) mineral oil sweet almond oil Miglyol 812 ©* (Table I). Table I Occlusivity and Delectric Constant of Oils P.H.S. Mineral Oil Sweet Almond Oil Miglyol 812 © Occlusivity % 78 _+ 5 35 -+ 4 28 +_ 4 57 + 3 Dielectric Constant 2,08 2,18 3,09 3,78 Two main groups of nonionic surface active agents were used for this study. One, with ester bonds: Montanox 80 ©** a sorbitan monooleate ester with an average of 20 ethylene oxide residues and Montane 80 ©** a sorbitan monooleate ester the other with ether bonds: Simulso192 ©** an oleyl alcohol derivative with an average of two ethylene oxide residues and Simulsol 96 ©** with an average of 10 ethylene oxide residues. The following HLB values suggested by the manufacturers were used for computing the HLB of the surfactant mixtures: esters { Montane 80©: 4.3 Montanox 80©: 15 Ethers { 92©: 4.9 Simulsol 96©: 12.4 Simulsol The emulsions were prepared by emulsifying the oil phase in demineralized water, after which they were stabilized with a mixture of surfactants by phase inversion (8). Three common formulae of emulsions were prepared (Table II). The binary mixtures of oil surfactant having the same oil/surfactant (O/S) ratio as in the emulsions were also carried out for various HLB. *Fatty acids triglycerid (C8-C•2) **Seppic-Montanoir, Paris, France.

OCCLUSIVITY OF AQUEOUS EMULSIONS 159 Table II Formula of Emulsions Formulas Constituent Oil Surfactant Water Oil/Surfactant Ratio A 5 5 80 3 B 10 5 85 2 C 10 10 80 1 PROCEDURE A 10% (W/W) gelatin solution in water was cast at 70øC to a thickness of 1 cm in a glass tube with an inner diameter of 3 cm. Relative humidity under the gelatin was maintained at 100% (7). The upper surface was in contact with air. The water contained within the gel was thus made to migrate in the same way that insensitive perspiration moves across the stratum corneum. The amount of water loss through the gelatin was determined gravimetrically in standard experimental conditions: 25øC and 60% RH. Water loss was measured 15, 30, 45 min. before application and 15, 30 ... 240 min. after application. The dose applied was 3 mg.cm -2 CALCULATION OF OCCLUSIVITY In order to express the occlusivity (Oc) of the preparation as a measure of resistance to water loss, occlusivity was defined by the following equation: WLB -- WLA Occlusivity (Oc)% = WLB x 100 WLB -- Water loss of the gelatin cell in mg.cm -2 min. -1 before application WLA--Water loss of the gelatin cell in mg.cm -2 min. -1 after application of the preparation. DEHYDRATION OF EMULSIONS The kinetics of dehydration of the emulsions have been studied at the same temperature and RH already described. The gelatin layer has been replaced by a sheet of aluminium paper as inert support, the dose applied was 3 mg.cm -2. So the kinetic of water evaporation of the emulsions was studied as a function of the time. Phase Diagrams in Oil-Surfactant- IVater Systems Ternary phase diagrams were constructed with various oils, mixtures of surfactants and water. The experimental procedure and determination of the phase limits were published previously (8). The percentage of the surface area occupied by the isotropic oil phase was calculated in relation to the totality of the diagram's surface for the different HLB values. STATISTICAL ANALYSIS Statistical significances were calculated using one way analysis of variance (9).