Influence of short chain alcohols on adsorption of sodium dodecylsulfate and Triton X-100 mixture at solution–air interface

Abstract

Measurements of the surface tension of the aqueous solutions of sodium dodecylsulfate (SDDS) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (Triton X-100 or TX-100) mixture with methanol, ethanol or propanol were carried out in the whole range of alcohol concentration and in the range of the surfactant mixture concentration from 1×10−5 to 5×10−3M. On the basis of the obtained results the surface excess concentration of the surfactant mixture and alcohol was determined and compared to the surface excess concentration of the particular components of the solution. Taking into account the values of the surface excess concentration of the surfactant mixture and alcohol obtained on the basis of the surface tension values of the aqueous solutions of the TX-100 and SDDS mixture with alcohol as well as the surface excess concentration of individual TX-100, SDDS and alcohol from their aqueous solutions, the mutual influence of the surfactant mixture and alcohol on their adsorption at the solution–air interface was considered. Therefore the alcohol activity at the solution–air interface was calculated by using the Sprow and Prausnitz equation. The mutual behavior of TX-100 and SDDS in the presence of alcohol was determined on the basis of Rosen's theory of regular solutions. The influence of the particular components of the water+alcohol solutions of the TX-100 and SDDS mixture was discussed in the light of the Gibbs surface free energy of adsorption of these components at the solution–air interface. This energy was determined by different methods and it appeared that the equation of Gu and Zhu proposed for the surfactant adsorption at the solid–solution interface was also useful for determination of the standard free energy of adsorption of alcohols at the solution–air interface.