COMPLEX FORMATION IN AEROSOLS 825 associated with complex formation, this would be considered evidence for the formation of the complexes. The data obtained with lauric, myristic, and palmitic acids in com- bination with triethanolmine are given in Table XIV. In the triethanol- amine laurate system, the addition of excess lauric acid had essentially no effect upon the properties of the system. There also was little effect upon foam stability. Foams from both mixtures wetted paper almost immediately after discharge and started to collapse. These results indi- cated that molecular complex formation was negligible in the triethanol- amine laurate systems. The addition of excess myristic acid to the triethanolamine myristate system had a noticeable effect upon the properties, however. Emulsion viscosity, emulsion stability, and foam stiffness increased, and the rate of drainage decreased. Foam stability was affected similarly. The foam with an excess of triethanolamine started to wet paper within 10 minutes, became very thin, and started to collapse. The foam with an excess of myristic acid showed little change after an hour. This effect of myristic acid upon the properties of the triethanolamine myristate system are typical of complex formation. In the triethanolamine palmkate system, excess fatty acid resulted in an increase in emulsion stability and in loam stiffness. The rate of drainage was low regardless of the acid/base ratio, and the foam stability was high. Foams with both acid/base ratios showed little change after two hours. It seems likely that strong molecular complexes between palmitic acid and triethanolamine palmitate were formed, regardless of the acid/base ratio. Table XIV Variation in Fatty Acid/Triethanolamine Ratio Foam Properties c, a Emulsion Properties Acid/Base Drainage Stiffness Acid Ratio (Mols) Viscosity Stability (60 min) (g) Lauric 1:1 •/• Low 1 rain 85 9 1:1•/• b Low 1 min 86 10 Myristic 1:1•/• (* Low 1 min 71 21 1 •/•:1 • Low to medium 1 hr 5 37 Pahnitic 1:1•/• a Low to medium 15-30 min 0 23 1 •/•: i v Low to medium 1 hr 0 42 1:1• ratio = 0.10 M acid/0.15 M base. 1•/•: 1 ratio = 0.15 M acid/0.10 M base. All discharges are quiet. All densities range from 0.060 to 0.069 g/cc.

826 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS DISCUSSION OF RESULTS The addition of many of the long-chain alcohols to aerosol emulsions based either on sodium lauryl sulfate or the triethanolamine salts of the fatty acids has a pronounced effect upon such properties as emulsion viscosity and stability and foam drainage, stiffness, and stability. These effects are similar to those observed previously in nonaerosol sys- tems and indicate that complex formation occurs between the surfac- rants and the alcohols in the aerosol systems. The aerosol systems used for the study were relatively simple. In aerosol products, where there may be many more ingredients, the effects of the added alcohols might be modified by the other components present, particularly if they were surface active. The molecular complexes generally had an observable effect on the properties of both the aerosol emulsions and the resulting foams. Com- plex formation, therefore, occurred initially at the propellant/water interface in the aerosol emulsions and subsequently influenced the properties of the foams when the emulsion was discharged. Complex formation probably occurred in the bulk phase of the emulsion by solubilization of some of the alcohol molecules in the surfactant micelles as well as at the propellant/water interface. The wetting properties of the foams on paper correlated well with the drainage rates and, in many cases, with foam persistence. The effect of the complexes in decreasing foam drainage was very marked and was consistent with the results reported on the effect of molecular complexes in nonaerosol foams. The effect of the complexes in decreas- ing foam drainage is considered to result from an increase in surface viscosity. In the present work, there were many cases in which an obvious decrease in foam drainage and an increase in foam stiffness could be interpreted on the basis of complex formation. In other cases, a decrease in foam drainage occurred, but there was no apparent increase in foam stiffness. It is probable that the foam stiffness measurements are much less sensitive than drainage tests and do not show increases in foam viscosity unless the increase is fairly large. Cholesterol had little effect upon the properties of sodium lauryl sulfate systems and apparently did not form strong complexes with sodium lauryl sulfate in aerosol systems. Previous work indicated that cholesterol did form complexes with sodium alkyl sulfates in nonaerosol systems. In triethanolamine palmitate and stearate systems, cholesterol in- creased foam drainage slightly and decreased foam stiffness. It also