THERMODYNAMIC STUDY IN AQUEOUS MICELLAR SOLUTIONS AT 298.15 K - COMPARISON OF THE INTERACTIONS BETWEEN IONIC SURFACTANTS (SDS AND CTAB) AND 1-ALCOHOLS OR PHENOL

Densities and heat capacities of the ternary systems water + surfactants (SDS or CTAB) + alcohols (C-4-C-6) or phenol have been measured in the aqueous domain at 298.15 K. Transfer molar volumes and transfer molar heat capacities of alcohols or phenol from water to water + SDS or water + CTAB were deduced therefrom. In both surfactants, the variations of the transfer quantities of alcohols are typical of the partition of an amphiphilic solute between aqueous and micellar phases, depending on its hydrophobicity, and moreover, they reveal postmicellar transitions. In contrast, phenol behaves differently. In SDS solutions, the variations of transfer properties are similar to what is observed with alcohols, but in CTAB solutions, particularly large variations are observed for a phenol/CTAB ratio of between 1 and 2. At the same time, the viscosity of these solutions increases, and viscoelasticity appears. The formation of a strong complex between the positive quaternary ammonium polar heads of the surfactant and phenol resulting from the weak acidic character of phenol, is certainly responsible for the evolution of the transfer properties and for the viscosity of CTAB solutions in the presence of phenol.