AEROSOL EMULSION SYSTEMS 277 that stream with the standard actuator will spray with the mechanical break-up type. "FREON ©" * PROPELLENTS STUDIED The propellents involved in the study were "12" (dichlorodi- fluoromethane), "114" (dichlorotetrafluoroethane), "11" (trichloromono- fluoromethane), and "1 lY' (trichlorotrifluoroethane). Although "11" and "11Y' are not normally considered as propellents because of their relative low vapor pressures at room temperatures, they will be considered as such in the present paper for ease of discussion. EXPERIMENTAL RESULTS Emulsion Stability with the Individual Propellents (17) The relative stability of water-in-oil emulsions prepared with the individual propellent compounds is as follows, in decreasing order: "11" "113" "12, .... 114." In Table 1 are listed the separation times for the emulsions prepared with various propellent/water ratios. The relative stability of the emulsions prepared with the propellent compounds corresponds roughly to the solvent properties of the compounds. This is indicated by a comparison of the Kauri-butanol values (8) for the propellent compounds that are also listed in Table 1. Actually propellent "12" and propellent "114" are such limited solvents that the Eracol 14 used as the emulsifying agent was not sufficiently soluble to form good emulsions. TABLE 1--EMULSION STABILITY OF PROPELLENT-WATER SYSTEMS* Propellent/Water Emulsion Separation Time Ratio, Wt. % Propellent "12" Propellent "114" Propellent "11" Propellent "113" 90/10 1 min. 1 min. 15-30 min. 1-5 min. 80/20 1 min. 1 min. 15-30 min. 1-5 min. 60/40 1 min. 1 min. 1 hr. 1 hr. 40/60 1-5 min. 15-30 min. 1 hr. 1 hr. Kauri-Butanol values of propellents 18 11.8 60.1 32 * 4 parts of Emcol 14/104 parts of emulsion. PROPELLENT-WATER EMULSIONS Satisfactory water-in-oil emulsions with "12"/"114" solutions or "114" alone as the propellent have not yet been achieved. As previously men- tioned, these two propellents have limited solvent properties and the sur- face active agents in general were not sufficiently soluble in the propellents to form stable emulsions. * Referred to by number only in remainder of paper.

278 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Propellents "12" /"11" / l/Fater Emulsions Fairly satisfactory emulsions may be obtained by combining "11"• with its relatively good solvent powers, with "12." The spray charac- teristics of the emulsions may be varied from very fine to very wet by varying either the "12"/"11" ratio or the propellent/water ratio. The effect of varying the "12"/"11" ratio upon spray characteristics and emulsion separation times is shown in Table 2. The variations were tested at propellent/water ratios of 80/20 and 60/40, respectively. As the data in Table 2 indicate, increasing the proportion of"l l" in the propellent TABLE 2--EffECT or VARIATION IN PROPELLENT "12"/PRoPELLENT "11" RATIO UPON EMULSION AND SPRAY PROPERTIES Propellent Propellent 12"/11" Spray 12"/11" Spray Ratio, Sepal, ation Charac- Ratio, Separation Charac- Wt. % Times teristics Wt. % Times teristics 80/20 Propellent/Water Ratio 60/40 Propellent/Water Ratio 100/0 (1 min. 100/0 1 min. 70/30 1 min. Very't•e 70/30 30-60 min. Fine'" 50/50 1-5 min. Fine 50/50 30-60 min. Medium fine 30/70 15-30 min. Medium fine 30/70 30-60 min. Soft medium 0/100 15-30 min. No spray 0/100 1 hr. No spray 4 parts Emcol 14/104 parts final emulsion mixture increases the stability of the emulsions and also the wetness of the spray. Both of these effects would be predicted on the basis of the data in Table 1 and the fact that "11" lowers the vapor pressure of "12," thus giving propellent mixtures that produce coatset sprays. The effect of varying the propellent/water ratio upon emulsion stability and spray characteristics is given in Table 3. In these experiments the "12"/"11" ratio was held constant at 30/70. TABLE 3--EffECT or VARIATIONS IN PROPELLENT*/WATER RATIO UPON CREAMING AND SPRAY CHARACTERISTICS Propellent/Water Separation Ratio, Wt. % Times Spray Characteristics 90/10 1-5 min. Very fine 80/20 5-15 min. Fine 60/40 30-60 min. Medium 40/60 1 hr. Very coarse--almost foams 20/80 1 min. Stream--foams Emulsions prepared with 4 parts Emcol 14/104 parts of finished emulsion * Propellent is "12"/"11" (30/70). In this series, increased emulsion stability and increased wetness of sprays result with a decrease in the propellent/water ratio. The increase in stability probably results primarily from the increase in viscosity of the