Micellar Properties and Related Thermodynamic Parameters of Aqueous Anionic Surfactants in the Presence of Monohydric Alcohols

Abstract

The effect of monohydric alcohols, (C7–C10), on the micellar behavior of anionic surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS), was investigated using experimentally measured densities, ρ, speeds of sound, u, and specific conductivities, κ, at various temperatures and atmospheric pressure. A number of thermodynamic parameters, like apparent molar volumes, Φv, partial molar volumes, Φov, isentropic compressibility, κs, and various thermodynamic parameters of micellization were calculated to elucidate the interactions prevailing in the studied aqueous surfactant–alcohol systems. The decrease in critical micelle concentration (cmc) on addition of an additive may be seen in terms of establishment of additional hydrophobic interactions between the hydrophobic part of the surfactant and additive molecules. It can be seen that ΔG°m < 0 is weakly dependent on alcohol concentrations in aqueous surfactant solutions. Further, 1H and 13C NMR chemical shift measurements in micelle solutions containing above-mentioned alcohols have also been carried out. From 1H and 13C NMR spectra, it was concluded that the site for preferential solubilization of alcohol is close to the headgroup of the micelle. The trend observed in carbon chemical shifts may be attributed to the chain length of the added alcohols due to the strong ion–dipole interaction between the negatively charged SDS headgroup and the hydroxyl group of the alcohol.