New Interpretation of Small System Thermodynamics Applied to Ionic Micelles in Solution and Corrin-Harkins Equation

Abstract

Surfactant micelle should typically be regarded as a small system characterized by non linear homogeneity of the thermodynamic functions. Aqueous micellar solutions of single component ionic surfactant with an electrolyte added have been treated by the small system thermodynamics. The functional form of chemical potential μM of interacting micelles in solution has been determined. The aggregation number distribution and the mean degree of counterion binding β of ionic micelles are discussed in detail, in which the condition to make β constant at given T and P is obtained. Corrin-Harkins equation and its linearity have theoretically been discussed in relation to the definitions of critical micelle concentration. The gradient of linear Corrin-Harkins plot can to good approximation presume the value of β of micelles in solutions at concentrations higher than CMC as well as at CMC. © 2004, Japan Oil Chemists' Society. All rights reserved.