Volumetric properties of sodium dodecylsulfate and Triton X-100 mixture with short-chain alcohol in aqueous solution

Abstract

Measurements of the surface tension, density, dynamic viscosity and specific conductivity of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (Triton X-100 or TX-100) and sodium dodecylsulfate (SDDS) mixture with a short-chain alcohol (methanol, ethanol or propanol) were carried out. The obtained results indicate that surfactants can aggregate in the presence of alcohol and vice versa. The concentration at which alcohol starts to form aggregates (CAC) depends only slightly on the surfactant mixture composition and concentration and it is close to that obtained for the aqueous solutions of a given alcohol. On the other hand, surfactant mixture can form micelles only in the range of alcohol concentration in which it is present in the monomeric form in the bulk phase. At very low concentration of ethanol and propanol, the CMC decrease of the surfactant mixture takes place. The obtained results indicate also that the apparent and partial molar volumes of water practically do not depend on the composition and concentration of the surfactant mixture and they are similar to those obtained in the aqueous solution of alcohol. However, the volumetric properties of alcohols depend somewhat on the composition and concentration of the surfactant mixture. Similarly to the aqueous solution of a single alcohol, the apparent molar volume isotherm of methanol in the studied solutions does not have any extremum contrary to ethanol and propanol. The apparent molar volumes of the surfactant mixture in the micellar state are higher than in the monomeric form. The composition of the mixed micelles reflects the tendency of TX-100 and SDDS to the micelle formation in their aqueous solutions in the presence of alcohol.