748 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (Type B Viscometer, Model BL, by Tokyo Keiki Seizosho, Tokyo, Japan) at 30 rpm using spindle No. 3. Viscosity measurements were taken after a l-rain rotation. All emulsifica- tion operations were done carefully to assure good reproducibility. All surfactants, oils and waxes used in the formulations were cosmetic grade materials without further purification, and &ionized water was used in all experiments. RESULTS AND DISCUSSIONS Although a great number of formulations representing a wide range of cosmetic emulsions and nonemulsions were tested by LEE in this series of investigations, because of the space limitation only the results from several representative formulations will be shown. These formulations are simplified prototype cosmetic emulsions including a cationic O/W emulsion, a nonionic W/O emulsion, a nonionic O/W emulsion and an anionic/nonionic O/W emulsion. The cationic O/W emulsion shown in Table I represents a prototype cationic hair rinse emulsion stabilized with a popular quaternary surfactant, stearyl dimethyl benzyl ammonium chloride. The results obtained with this cationic O/W emulsion are shown in Figure 2 where the arithmetic mean droplet diameters are plotted against c•H, the percentages of water withheld for second-stage dilution. The initial temperatures of first-stage emulsification, Te, are also indicated in the figure. It is clear from Figure 2 that the emulsion becomes coarser as the emulsification temperature, Te, is lowered. The mean droplet size also increases somewhat as c•H is increased beyond 50%. Below 50% c•H, the variation in the mean droplet sizes was within the experimental error. The result is not surprising since it is expected that as emulsification temperature is lowered, emulsification becomes less efficient due to a viscosity build-up. However, for this system, no significant increase in the mean emulsion droplet size is observed until c•H is well over 50%. This means that as much as 50% of the external phase (water) of this emulsion could be withheld for a later addition at room temperature to save a considerable amount of thermal energy without adversely affecting the emulsion quality. In general, it is easier to carry out LEE on O/W emulsions containing low solids such as a moisturizer with 70% or more external, aqueous phase. However the applicability of LEE is by no means restricted to O/W emulsions. It also works satisfactorily for W/O emulsions containing a large amount of mineral oil. An example of such a W/O emulsion is given in Table II. Table I Cationic O/W Emulsion Wt. % Stearyl Dimethyl Benzyl Ammonium Chloride (21% activep Light Mineral Oil Stearyl Alcohol Water 4.0 4.0 1.6 90.4 100.0 a Rohm & Haas Co., Philadelphia, Pennsylvania.

EMULSION QUALITY 749 • • I 1 CATIONIC O/W EMULSION 55- ß o ,.• z )øC 0 I0 20 :50 40 50 60 70 80 90 I00 % WATER WITHHELD, •1• Figure 2. Effect of o/H and emulsification temperature on droplet size of the cationic O/W emulsion The external phase of this W/O emulsion is mostly mineral oil. Varying amounts of pure mineral oil were withheld for later dilution at room temperature after completion of the first stage emulsification. It is clear from Figure 3 that LEE worked satisfactorily at an emulsification temperature of 80øC up to c• o = 70. A sharp increase in mean droplet size, indicating a degradation of the emulsion, was observed between c• o = 70 and c• o = 80. From conductivity measurements it was found that the emulsion inverted from a W/O type to an O/W type at c• o values above 70. Since the intended emulsion was a W/O type, the phase inversion resulted in the formation of coarse emulsions. The reason for the phase inversion at a high cr o value is r•adily understood from the illustration in Figure 4. The dashed line in the figure represents the boundary between the first portion of the external phase used for the emulsification and the second portion used for dilution. As cr o is increased, the boundary is lowered and the ratio of the first-stage Table II Nonionic W/O Emulsion Wt. % Water 30 Diethyleneglycol Distearate 1 Polyoxyethylene (20) Sorbitan Monostearate a 4 Sorbitan Sesquioleate a 8 Light Mineral Oil 57 100 a Kao-Atlas Co., Ltd., Tokyo, Japan.