AEROSOL EMULSIONS AND FOAMS 631 smaller droplet size ranges and better stability. The foams have better sta- bility and lower drainage. Photomicrographs (300x) of the emulsions are illustrated in Fig. 2. The superio•'ity of the excess triethanolamine aerosol emulsions from the best con- centrate are readily discernible by the smaller drop!et diameters. The drop- lets in the aerosol emulsions from the excess myristic acid system are not suf- ficiently clear to draw any definite conclusions. The emulsions were too opaque to allow sufficient light transmission for a satisfactory photomicro- graph. •.• •. ? , • ... lip . •' .. ..•: :. ... .. , ß .... :. •.. ,. .. .:% •. ..,.::• .•.' ¾'•7P2:'•'•.., •..•:.'•.'.. •'* "•' '. ...... -. '_ ..•..•...:..•:'.•... :".•:' • t%. •:..... Figure 2. Photomicrographs of aerosol emulsions (300X) of aqueous triethanolamine myristate/mineral oil / Freon 12 / Freon114 (40 / 60) aerosol emulsions Top. Excess myristic acid. Left, aerosol emulsion from best mineral oil conc. Right, aerosol emulsion from poorest mineral oil conc. I•ottom. Excess triethanolamine. Left, aerosol emulsion from best mineral off conc. Right, aerosol emulsion from poorest mineral oil conc. Increase in Foam Bubble Size With Age The diameter range of the emulsified droplets in the concentrate, aerosol emulsions, and bubbles in the foams are listed in Table V. The data show that concentrates and aerosol emulsions with the smallest droplet size range also produce foams with the smallest bubble size range. The increase in bubble diameter in foams with age has been reported pre- viously (1). The data in Table V show that the range of bubble diameters in the foams from the best concentrates are smaller initially and remain smaller as the foam ages. Photomicrographs of one of the foams for periods up to 10 min after dis- charge are shown in Fig. 3.

632 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table V Increase in Bubble Size Range with Age of Foams from Aqueous Triethanolamine Myristate/Mineral Oil/Freon Propellant Systems Aqueous Concentrate Method of preparation TEA/MA ratio Diameter range of emulsified droplets (t•) Aerosol Emulsion Diameter range of emulsified droplets Aerosol Foams Dianaeter range of bubbles with age (t•) 1 rain 2 rain 5 rain 10 rain I 14 I 14 Excess Excess Excess Excess MA MA TEA TEA 2--5 • 2--35 • 2--70 15--190 ( 2-40) ( 2-40) (Rough (Rough estimate) estimate) 2-8O • 2-120 10-80 10-115 15-140 20-175 20-140 25-170 25-215 20--245 30-205 35-220 65-360 50-410 55-265 50-275 110-600 95-• 700 Figure 3. Increase in bubble size xvith age of foams from the best aqueous triethanolamine myristate/mineral oil/Freon propellant aerosol enmlsion xvith excess myristic acid Top left. I min right, 2 min Bottom left. 5 rain right, 10 rain Effect of Discharge of the Aerosol Emulsion The rango of droplet sizes of the dispersed propellant in an aerosol emul- sion has been shown to decrease as the product is discharged (1). This also occurs when the propellant/mincral oil emulsions are discharged as shown by the data in Table VI and the photomicrographs in Fig. 4. The change is