含エステル基界面活性剤の研究エタノール-水混合溶液中でのミセル形成

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The critical micelle concentration (cmc) values of seven sodium sulfoalkyl alkanoates, CnH2n+1 COO (CH2) mSO3Na, with the number of carbon atoms n=9, 10 and 11; m=2, 3 and 4 in the ethanol-water mixture were measured by the spectral change of pinacyanol chloride. The cmc values of n=9 derivative series decreased linearly with the increase of ethanol concentration. While the cmc values of n=10 and 11 derivative series showed a minimum and then increased markedly with the ethanol concentration. These phenomena suggest that the decrease of cmc is due to partly solubilized ethanol in the micelle of the surfactant, and that the increase of cmc is due to the increased solvent power of ethanol-water mixture solvent. The results indicated that the effect of ethanol-water mixture solvent on the cmc value is greatly dependent on the position of the ester group in the alkyl chain of the surfactant. Namely, the cmc decreasing-power of the methylene unit situated between the ester and sulfonate group is more than that of the methylene unit in the fatty acid portion. On the other hand, the effect of variation of alkyl chain length in the fatty acid portion was more than that of alkyl chain length situated between the ester and sulfonate group on the cmc increasing-power.
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