The critical micellization temperature and its dependence on the position and geometry of the double bond in a series of sodium octadecenoates

Abstract

The temperature-induced changes in the infrared spectra of a series of sodium octadecenoates have been used to investigate the temperature-induced micelle formation in deuterium oxide, and to compare the effect of the configuration and position of the double bond on this phenomenon. The critical micellization temperatures were determined from typical frequency versus temperature plots. For any given pair of geometrical isomers the difference between the cis and trans configuration is 29°C, the trans isomers having the higher critical micellization temperature. The relationship between the position of the double bond and the critical micellization temperatures of the sodium soaps on one hand, and the melting points of the fatty acids on the other hand, is different. Among the cis octadecenoates, sodium oleate has the highest critical micellization temperature while oleic acid had the lowest melting point among the cis octadecenoic acids.