Properties of Micellar Solutions of Sodium Decyl Sulfate at Relatively High Concentrations

Heat capacities of aqueous solutions of anionic surfactant sodium decyl sulfate in the 0.28–0.42 mol kg −1 range of molar concentrations and the 278–363 K range of temperatures are studied via precision adiabatic differential scanning microcalorimetry. Specific and apparent heat capacities of solutions at intervals of 0.01 mol kg −1 , partial molar heat capacities of the solute and the solvent, and excess partial molar heat capacities are plotted as functions of concentration and temperature. The Kraft boundary is determined. Analysis of the characteristic changes in the above properties reveals structural changes in sodium decyl sulfate micelles that correspond to their shape transforming from cylindrical to plate-like in the region of the third critical micelle concentration.