Osmotic pressure of micellar sodium dodecyl sulfate solutions in the presence of NaCl

The concentration dependence of osmotic pressure π_s of micellar solutions of an ionic surfactant in the presence of a background electrolyte is theoretically considered in terms of the Debye-Hückel theory with due regard for the premicellar association and interaction of micelles. On the basis of the quasi-chemical theory of micellization, the system composition is determined and the thickness of the electrical double layer of micelles is calculated. Within the framework of a cell model and the ideas of the molecular and ion-electrostatic interaction of micelles, which varies in relation to the degree of micellization, osmotic pressure in a sodium dodecyl sulfate-0.01 M NaCl system is calculated during variations in the overall surfactant concentrations. The results obtained are in good qualitative and quantitative agreement with available experimental data. At the same time, the results of calculating π_s values in terms of the Debye-Hückel theory without consideration for the interaction of micelles do not allow explanation of the experimental regularities.