Effective interaction between reverse micelles: A study from the potential of mean force at infinite dilution

The effective interaction potential between reverse micelles is computed by adding the potential of mean force at infinite dilution to the direct interaction between micelles. The former is computed from an integral equations approach and the latter is modeled by van der Waals and electrostatic contributions. This model is used to discuss the characteristics of the effective interaction—range, strength, and temperature dependence—deduced in previous work from the effective one-component approach. From a detailed analysis of the various contributions to the effective interaction, it is concluded in agreement with other studies, that the relative long range of the interaction is attributed to electrostatic contributions. The moderate interaction strength is found to result from strong cancellations between direct interactions (short range repulsion plus van der Waals attraction between surfactant films) and indirect ones (“depletion” plus “solvation” effects). In contrast with previous studies which attributed the increase with temperature of the interaction strength only to the extension of surfactant chains (direct interaction), the variation with temperature of the potential of mean force is found to be equally important.