INFLUENCE OF OLEIC-ACID ON THE STRUCTURE OF A MIXTURE OF HYDRATED MODEL STRATUM-CORNEUM FATTY-ACIDS AND THEIR SOAPS

The phase behaviour of a hydrated (32% (w/w) water) mixture of saturat ed and unsaturated fatty acids and their soaps has been examined. By p rogressively increasing the proportion of oleic acid, it could be show n that this unsaturated component exists partly as a separate phase wi thin the others. The unsaturated fatty acids form an H(II) phase at 25 -degrees-C, whereas the saturated fatty acids form a fatty acid-soap c rystal under the conditions employed. The results help to explain the role played by the fatty acids (and also cholesterol) within the lipid fraction of human stratum corneum. A feature of this study is a compa rison of the results obtained by X-ray diffraction, differential scann ing calorimetry and Fourier transform infrared spectroscopy.