The Gibbs-Helmholtz equation and the enthalpy–entropy compensation (EEC) phenomenon in the formation of micelles in an aqueous solution of surfactants and the cloud point effect

Abstract

Here, the hidden thermodynamic processes in the micellization of an aqueous surfactant solution are analyzed analytically. Based on the hidden processes, an equation for the self-association process was obtained, which represents the Gibbs-Helmholtz equation. For the existence of the enthalpy–entropy compensation (EEC) effect, the temperature dependence of the Gibbs free energy of micellization is necessary. In order to compare the EEC parameters of the clouding point effect with the EEC parameters of micellization, it is necessary to observe the clouding process in the direction of the surfactant transfer from the aqueous solution to the crystalline phase (opposite to what is usual in the literature). EEC parameter b (enthalpy change when entropy changes have the zero value) in the micellization process always has a negative value. In contrast, in the clouding point effect process, it can have both positive and negative values.