220 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table IV Effect of Various Amines at 1.1 X 10-aM on Emulsion Stability Expressed as Per Cent Oil Released at 13,000 rpm for 30 Minutes No 2- pH Amine n-Hexyl Ethylhexyl n-Octyl n-Decyl n-Dodecyl 8 9 9 9 10 10 11 70 74 78 8 2 6 0 4 8 2 6 0 100 .... No emulsion ... No emulsion 100 .... 100 No emulsion No emulsion ... I 10 99 No emulsion No emulsion ... 1 8 96 No emulsion 100 ... 1 6 92 No emulsion 95 ß.. 1 4 87 100 93 ... 1 3 82 95 87 ß.. 1 3 72 86 79 ß.. 2 3 20 57 65 ß.. 2 2 5 17 10 ... 2 2 ... 3 3 Tablc V Lowest pH Required to Produce "Stable" Emulsions (• 50-/o Oil Separated on Centrifugation) Concentration Neutralizing Amine X 10-aM n-Hexyl 2-Ethylhexyl Octyl Decyl Dodecyl 0.5 .............. 5.8 1.0 .............. 6.2 2.7 6.6 7.0 7.4 7.8 7.8 5.4 6.6 6.2 7.8 8.6 9.0 8.1 a b 10.2 10.2 10.6 11.0 c 9.0 10.6 11.0 11.0 aStable at pH 6.6. No lower pH value could be obtained at this concentration. bStable at pH 6.2. No lower pH value could be obtained at this concentration. •Stable at pH 7.2. No lower pH value could be obtained at this concentration. As the chain length of the neutralizing amine was increased, the pH at which "stable" emulsions could be produced generally increased. This was [urther verified by noting the effect of lower concentrations of dodecylamine. Whereas, at a concentration of 2.7 X 10-•M, a pH of 7.8 was required to produce "stable" emulsions, at levels of 0.5 and 1.0 X 10-•M dodecylamine only a pH of 5.8 and 6.2, respectively, was required (Tables V and VI). Furthermore, as the concentration of the amines was increased, higher pH values were needed to produce "stable" emulsions. Thus, as the hydro- phobic properties of the polymer-amine salt were increased either by react- ing more amine with the polymer or increasing the chain length of the neutralizing amine, a corresponding increase in hydrophilic properties was

STABILITY OF EMULSIONS 221 Table VI Effect of Lmv Concentrations of Dodecylamine on Emulsion Stability Expressed as Per Cent Oil Rdeased at 18,000 rpm for 30 Minutes Concentration X 10-3M pH 0.5 1.0 1.5 2.0 2.7 5.0 5.4 5.8 6.2 9 46 No emulsion No emulsion No emulsion 50 67 69 No emulsion 100 4 54 82 82 96 3 5 26 47 94 Table VII Effect of Mixtures of Hexylamine and Dodecylamine at Total Amine Concentration of 2.7 X 10-aM on Emulsion Stability Expressed as Per Cent Oil Released at 13,000 rpm for 30 Minutes Mole Fraction of Hexylamine pH 1.0 0.75 0.50 0.25 0 5.0 62 ...... 84 Noe•nulsion 5.4 66 69 79 ... 100 5.8 55 79 76 79 96 6.2 23 94 92 91 94 6.6 3 87 82 ... 82 7.0 3 8 11 10 42 7.4 4 3 3 3 7.8 4 4 4 ... 4 8.2 5 4 ..... 4 8.6 5 ... 4 6 6 required to maintain the polymer-amine salt at the oil-water interface (Table V). The n-hexylamine, however, produced "stable" emulsions independent of concentration in the range studied, while the 2-ethylhexylamine showed no definite trend as a function of increasing amine concentration. The reason why these two amincs behaved differently from the longer chain length amincs is not clear from this study. It should be noted also that once this level of stability was reached, further increases in pH by the addition of NaOH had no influence on emulsion stability. Thus, it appears that the amine salt is not dissociated even at pH values of 11.0, nor are the amphiphilic properties of the polymer significantly modified by the addition of the NaOH once this level of stability is achieved. The addition of the butylamincs (n-, ism, see-, and tert-butylamines) does not improve emulsion stability at concentrations up to 1.1 X 10-'-'M. Apparently the hydrophobic l•ropcrtics of these short-chain, water-soluble amincs are not sufficient to influence the polymer-oil interaction.