Thermodynamic Parameters of Anionic Surfactant−Additive Systems at the Cloud Point

Abstract

The thermodynamic parameters of an aqueous anionic surfactant, tetrabutylammonium dodecyl sulfate (TBADS), are calculated in the presence of various additives (viz., quaternary bromides, alcohols, and amines) at the cloud point (CP) of the TBADS−additive system. As the clouding components release their solvated water, they separate out from the solution. Therefore, the CP of an amphiphile can be considered the limit of its solubility. The standard Gibbs energy change of solubilization (ΔsG°) for all of the additives is found to be negative. The standard enthalpy change (ΔsH°) and the standard entropy change (TΔsS°) values are found to be negative as well as positive depending upon the type and nature of the additive. The results are explained on the basis of their nature, effect on the water structure, and solubilization of these additives either in the micellar or aqueous phase.