A conductometric study of dimethylsulfoxide effect on micellization of sodium dodecyl sulfate in dilute aqueous electrolyte solutions

Critical micelle concentrations (CMCs) of sodium dodecyl sulfate (SDS) have been determined in aqueous mixtures of dimethylsulfoxide (DMSO) between 25 and 45 °C and at very low NaBr concentration range (0.0025–0.03 mol dm−3). The ability of NaBr to lower the CMC in water is inhibited by DMSO below ∼0.014 mol dm−3 of NaBr. However, the contribution of DMSO in regard to its effect upon micellization process of SDS in aqueous electrolyte solutions have been discussed in terms of the observed behavior of thermodynamic properties, such as entropy (ΔSm°), free energy (ΔGm°) and enthalpy (ΔHm°). In particular, we discuss counterion binding as revealed by different experimental conditions. The data suggest mass action effect and salt-induced increase in micelle size with concomitant reduction in charge density of Stern-layer. These observations point to the counterion solvation effect of DMSO in addition to the loss of hydrophobic interactions due to strong intermolecular interactions.