Influence of solvent permittivity and divalent salt on micellization behavior of sodium dodecyl sulfate: Conductivity measurements and simulation study

Precise conductivity measurements of sodium dodecyl sulfate (SDS) solutions with and without manganese sulfate in water and ethanol–water mixture containing (10, 20 and 30) volume % ethanol is carried out at 298.15 K. The conductance decreased on the addition of ethanol with and without salt. From the pre-micellar and post-micellar slopes, the degree of dissociation (α) of SDS was calculated. On increasing the ethanol content, the α and critical micelle concentration (CMC) increased whereas they decreased with the addition of salt. Utilizing these CMC and α values, the standard free energy of micellization  was assessed. The negative values of  decreased when ethanol whereas increased with salt were added. Micellization of SDS was tested for several solvent parameters and solvophobic parameter. The free energy of surfactant tail transfer  was also evaluated. Conductivity data were also estimated with molecular dynamics simulations from GROMACS-5 software and the results showed good agreement with the experimental values.