Effects of 1-propanol (1P) addition on the micellar and thermodynamic parameters of aqueous solutions of anionic surfactants sodium dodecyl sulfate (SDS) and sodium dodecyl sulfonate (SDSn) was investigated by experimentally measured electrical conductivities, densities and sound velocities at 298.15 K. The values of the critical micelle concentration (CMC) of both surfactants in the investigated mixed aquo-1P solvents (wt% 1P 2.5, 5, 7.5 and 10) are smaller than those in pure water and the CMC decreases with increasing 1P concentration in solution to a minimum at (w/w) % 1P = 5 and then increases. However the values of the counterion condensation on the micelle decrease with an increment in the amount of 1P. Furthermore the values of the apparent molar volume and isentropic compressibility of the monomeric and micellar forms of the investigated surfactants were obtained from the experimental density and sound velocity data. It was found that, although the values of the apparent molar properties of micellar form of surfactants increase by increasing the organic solvent content, the values of the apparent molar volume of the monomeric form of the surfactants decrease with increasing concentration of 1P.
