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

Abstract 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 ( Δ G m ° ) was assessed. The negative values of Δ G m ° 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 ( Δ G trans ° ) 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.