Thermodynamics of Mixed Micellization of Isomeric Hexanediols in Sodium Dodecyl Sulfate

Abstract

The thermodynamic parameters of mixed micelle formation (Δ mic G°, Δ mic H°, Δ mic S°) have been determined for a series of mixed micelles consisting of two isomeric hexanediols (1,2-hexanediol and 1,6-hexanediol) in sodium dodecylsulfate micellar solutions. The enthalpies of micellization were determined directly from isoperibol solution calorimetry. Gibbs energies and entropies of micelle formation were obtained from the application of the charged pseudo-phase model of micelle formation to the calorimetric critical micelle concentration values. The location of the alcohols in the micellar palisade layer has been determined from two-dimensional nuclear Overhauser enhancement spectroscopy (NOESY) experiments. The calorimetric titration data indicates that the placement of the hydroxyl groups on the six carbon backbone greatly affects the energetics of the micelle formation process. From the NMR data, the location of the cosurfactant in the micelle has been determined. These results indicate that the locus of solubilization affects the subtle balance of forces responsible for the formation of the mixed aggregates.