196 JOURNAL OF COSMETIC SCIENCE SURFACTANT ASSOCIATION STRUCTURES AND PHASE CHANGES DURING EVAPORATION OF COSMETIC EMULSIONS •P. Aikens, 2S.E. Friberg, 2T. Huang, 2y. Yang, 2H. Yang •ICI Surfactants, Wilmington, DE 19850 2Dept. of Chemistry, Clarkson University, Potsdam, NY 13699 INTRODUCTION: The changes which occur due to evaporation in a cosmetic emulsion after application to the skin can have a signill- cant impact on the performance and efficacy of the product. In a straightforward water/non-volifile oil/surfactant system, the evaporation of water increases the relative concentrations of oil and surfactant, causing surfactant association structures such as hexagonal or lamellar liquid crystalline phases to appear. The path taken follows a straight line from the 100% water comer of the ternary phase diagram through the formulation point (Figure 1)' ff the oil has a high vapor pressure. ff the oil is volatile, a more complex curved path from the water corner results. Figure 2 shows the exact phase changes in the W/O emulsion at various points marked along the evaporation path. Implications from a skin-care point of view are that the formulation could pass through or end up in a 1,2 or 3-phase region during the evaporation process, depending on initial composition and also that chemical potential of actives can be controlled 2. The phase behavior of water, vegetable oil, nonionic surfactant and the sunscreen active octyl dimethyl p-amino benzoic acid (ODP) 3 is examined as well as that of the humectant polymer sodium hyaluronate in water and surfactant 4. EXPERIMENTAL METHODS: Phase Diagrams: Maximum solubility boundaries were determined visually at•er titration with oil or water. Liquid crystalline phases were identified and differentiated by patterns produced under mss-polarized optical microscopy and also by low angle X-ray diffraction. Emulsion Preparation: Water and polysorbate-80 are mixed and soy oil added with thorough mixing. Centrifugation of the W/O emulsion separated the oil and aqueous phases which were used as described below. Evaporation Studies: Samples of water, fragrance oil, surfactant were stirred in a Petrii dish at 22øC and weight monitored. At certain points along the evaporation path, determined by weight loss of water, samples were subjected to gc analysis to determine vapor pressure. For the microscopic observation studies of W/O emulsions, a small droplet of oil was placed on a microscope slide and aqueous solution introduced with a syringe and the changing phase behavior observed under crossed polarized microscopy and weight changes monitored. For O/W emulsions, the emulsion is applied to a confined area of a slide and visually observed under the microscope during evaporation. RESULTS AND DISCUSSION: Liquid crystalline phases can be formed in even simple systems such as sccn in Figure 1. Surfactant association structures are formed from water and surfactant. A miceIlar solution is formed up to 40% surfactant (in equilib- rium with oil) after which a hexagonal liquid crystalline phase appears. This is in equilibrium with oil and an aqueous solution with maximum surfactant. Another triangular 3-phase region is sccn with the hexagonal liquid crystal in equilibrium with the oil and a surfactant-oil (L2) solution. Evaporation paths for the W/O and O/W emulsions are traced with a dashed line. The W/O emulsion of water, soy oil and polysorbate-80 between crossed polarizers under the optical microscope is shown Figure 2. Initially, the view is black for the oil and aqueous isotropic liquid phases. Photo 1 shows a thin radiant band which appeared as the liquid hexagonal crystalline phase appears at point b on the phase diagram in Figure 1. This birefringent area grew (photo 2) to cover the entire droplet, seen in photo 3. Photo 4 shows the liquid crystalline phase diminishing as it is replaced by isotropic solution the droplet again appears black at the end (photo not shown).

PREPRINTS OF THE 1998 ANNUAL SCIENTIFIC SEMINAR 197 Figure 3 shows an example of the phase behavior of the sunscreen active ODP in water and laureth 4. The evapo- ration paths of an initial 2-phase (water and lameliar liquid crystal) and 3-phase (water, laureth 4-ODP solution and lameliar liquid crystal) formulation are traced by the dashed lines. Again, the various phases can be seen by polarized optical microscopy at paints along the water evaporation path. The location of ODP in the lameIlar liquid crystalline phase was determined by low angle X-ray diffraction and by UV spectroscopy to be in the B region of the bilayer, shown in Figure 4 while the vegetable oil was distributed between regions B and C. Another interesting system which was examined was that of the moisturizing polymer hyaluronic acid (in sodium salt) a and water in the presence of either polysorbate 80, (which gave a hexagonal liquid oTstal) or a phospholipidffatty acid emulsifier (giving lamellar liquid crystals). As water evaporated from the laureth 4 system, polarized light microscopy showed the appearance of lyotropic nematic liquid crystalline structures. This could not be reproduced by mixing/heating the components together in the ratio at which the structure appeared, it only could be formed during the slow evaporation process. o Figure •wp• a•rm orso• o• Po• •0 w• • a•rt=vap•alJmPaihsfcrW/OnndO/W -Enn• ' Figure 3. Ptmse Diagram of ODP, Lmm• 4, Water REFERENCES: Figure 2. Polarized •t Micro•eope • of Points i, 2, 3, 4 of W/O Formulation. Figure ! z 2'//././/. ' 1.) Friberg, S.E., Huan& T., Aikens, P. A., Colloids SurfacesA: Phys•ochem Eng. Aspects, 121, 1, (1977) 2.) Friberg, S. E., Brin, A-J., J. Soc.-Cosmet. Chem., 46, 255, (1995) 3.) Friberg S. E., Yang• J., Yang, I•, Aikens, P. •,J. Ar• Oil Chem. Soc., in press 4.) Friberg, S. E., Yang, tL, Aikens, P.A., submitted for publication