206 JOURNAL OF COSMETIC SCIENCE 95 ,' 5 Water 0 ø\ø 97.5 ½, III ! 2.5 5 % Laureth 4 -• Figure 2. The composition of emulsions a-j, Table I, marked on a triangular phase diagram. LIGHT SCATTERING Dynamic light-scattering (DLS) measurements were performed on a Brookhaven Instru- ments system. The light source was an Argon ion laser (Lexel Laser Model 85) operating at a wavelength of 514.5 nm, and scattering at 90 ø was collected. The samples for DLS were along the line pointing to the water corner, with a constant PEA/laureth 4 ratio at 3:7, and along the demixing line in the oil phase with maximum water content. The viscosity of the point with 15% water was chosen as the continuous-phase viscosity to convert the diffusion coefficient of the inverse micelies into a hydrodynamic size. The absolute magnitude of the size is subject to the limitations in the selection of the viscosity and the resolution of the instrument, and is no better than + 15%. RESULTS The complete phase diagram of the emulsion system has earlier been described (19), and the present description will be limited to those features that are essential for the report. In the emulsions, the phase equilibrium with the aqueous solution of the phenethyl alcohol changes (Figure 3) depending on the surfactant/phenethyl alcohol ratio. For

MODEL FRAGRANCE EMULSION SYSTEM 207 Phenethyl Alcohol L2 Water LLC Laureth 4 Figure 3. The phase diagram of water-laureth 4-phenethyl alcohol. L 2 = isotropic liquid (inverse micellar solution, W/O microemulsions) LLC = lameliar liquid crystal. Table II Diameters of Microemulsion Droplets in the Microemulsion Region From Light Scattering Laureth 4 (%) PEA (%) Water (%) Diameter (nm) 59.7 25.3 15 2.4 _+ 0.4 56.1 23.9 20 3.1 + 0.4 52.8 22.2 25 3.9 -+ 0.4 49.2 20.8 30 4.4 _+ 0.4 46 19 35 4.8 _+ 0.5 41.5 17.5 41 5.1 _+ 0.4 39.6 16.9 43.5 5.6 _+ 0.5 3 90 7 • 31 61 8 • 45 40 15 b 50 25 25 2.7 +_ 0.4 Scattering too weak. Some scattering, but cannot be resolved into reasonable size. aqueous solutions of phenethyl alcohol in the concentration range 2.2-1.5%, the equi- librium is with an oil liquid phase, a phenethyl alcohol/surfactant solution saturated with water. This oil phase does not contain any association structures for a surfactant/ (alcohol + surfactant) weight fraction less than 0.53 (Table II), while inverse micelies form in the solution for surfactant/alcohol ratios in the range 0.53-0.70 according to the