The electrical double layer of micelles in ionic surfactant solutions in the presence of a background electrolyte: 2. Moderately concentrated micellar solutions of sodium dodecyl sulfate

To continue previous studies [1], a model is developed for calculating electrostatic potentials (1)psi(0) and (1)psi(d) corresponding to the surface of micelle core and the Stern layer, respectively, and the degree (1)beta of binding of counterions in moderately concentrated micellar solutions of ionic surfactants. By the example of sodium dodecyl sulfate micellar solutions, dependences of (1)psi(0) and (1)psi(d) on overall concentration n varying over the range from 0.1 to 0.9 M are determined at different NaCl concentrations in the system. The absolute values of (1)psi(0) and (1)psi(d) potentials are found to grow with a rise in the degree of micellization and a reduction in the average intermicellar distances. This growth is greatly pronounced at a low content of the background electrolyte, whereas, in concentrated NaCl solutions (of approximately 0.1 M), potentials (1)psi(0) and (1)psi(d) remain practically constant. Dependence 1 - (1)beta(n) is monotonically decreasing function.