MODEL FRAGRANCE EMULSION SYSTEM 2 ! 5 Table III Separation Rates and Average Droplet Size, Both Measured and Calculated, of Emulsions 1-5 Average droplet radius (10 -5 m) Emulsion Separation rate (hr) Measured Calculated 1 2/3 2.5 2.9 2 10 1.5 1.4 3 12 1.2 • 4 1.5 2.0 2.1 5 15 min--2 layers __b __b 5 hr--3 layers • The error in measuring the density made the calculation of Ap, and hence the calculation of the average droplet radius, not possible. • No droplets could be observed microscopically after mixing. Water Figure 8. The oil phase in emulsion 4 consists of a W/O microemulsion, (W/O laem)/W.

216 JOURNAL OF COSMETIC SCIENCE Figure 9. Photograph of emulsions 1-10 between crossed polarizers viewed against a light source. This approach implies an assumption that the liquid crystal forms a fractal structure with a constant area perpendicular to its direction of extension, a reasonable assumption. Hence the characteristic length of the dispersion system becomes proportional to the liquid crystal fraction of the dispersed phases. Using equation 5 a linear curve is obtained from the double-logarithm plot of the percentage of stable emulsion versus the liquid crystal fraction of the dispersed phases (Figure 11). The slope of the line (Figure 11) gives an estimation of the order of dimension of the system, approximately 2.5, which is not unreasonable considering the structure of the lameliar liquid crystal. Final explanation of this result must await exact structural determinations of these emulsions, but it is obvious that "emulsions" 8-10 and "emulsions" i and j in Figure 4 are in fact vesicle dispersions (24). Laureth 4 has been shown readily to form stable vesicles (29), and the stability of the vesicular dispersion is expected. The fact that the tie-lines (Figure 3) emanate from aqueous solutions of low concentra- tions of the alcohol and the fact that the evaporation of alcohol is negligible compared to that of water means that the vapor pressure of the alcohol remains approximately constant one half hour after application. It has been found that most of the water in skin-care formulations is evaporated within 30 minutes after application (30) and that the values of vapor pressure in the used system (19) allow an estimation of the vapor pressure of the present emulsions. The vapor pressures are given in Table IV. It is highly noteworthy that the vapor pressures of emulsions 4-7 in Figure 4A remain at such a high level, only 32% lower