Abstract
Critical micelle concentration (cmc) of three kinds of sodium sulfoalkyl alkanoates, having linear alkyl chain with total of 14 carbon atoms, has been measured by electrical conductance of each aqueous solution at temperature ranging from 15° to 50°C. Variation of the cmc with the temperature exhibited a minimum for all the surfactants. The positions of minima in the cmc shifted toward lower temperature side with change of position of the ester group away from terminal to the center of hydrocarbon chain of the surfactant.
The percentage deviation of the cmc values, obtained in different temperatures, from the value of the cmc at 30°C was plotted as a function of temperature for these surfactants. In the temperature range below the cmc minimum, the deviation of these surfactants decreased in accordance with the ester group position moved farther away from the terminal sulfonate group. But in the temperature range above the cmc minimum, the difference among the three deviation values became smaller and their magnitude were not in order. This phenomenon suggests that the hydration of the ester group is effected by a change in water structure with temperature and by the position of ester group in the alkyl chain of the surfactant. Also this proposal could be confirmed from the enthalpies and entropies of micelle formation.
