The Study of the Adsorption of Detergents at a Solution-Air Interface by Radiotracer Method. III. The Effect of Inorganic Electrolytes on the Adsorption of Sodium Dodecyl Sulfate

Abstract

Abstract The direct measurement of the adsorption of 35S labelled dodecyl sulfate ion at the solution surface and the measurement of the surface tension were carried out on the aqueous solutions of sodium dodecyl sulfate containing a given concentration of an excess salt. The salt concentrations studied were 0.01, 0.1, 0.3, 0.5 and 1n for sodium chloride, and 0.1 n for potassium-magnesium, manganous and aluminum chlorides. 1. The adsorption of dodecyl sulfate ion reaches equilibrium within one minute for all the systems under investigation. 2. The presence of excess of salt gives rise to the remarkable increase in the adsorption of dodecyl sulfate ion, but at the concentrations of excessive salts of about 0.1 n or more, the effects of the concentration and nature of the salts on the adsorption of dodecyl sulfate ion are not so appreciable. 3. The adsorption of dodecyl sulfate ion was well expressed by the Gibbs adsorption equation of n=1 for the systems under investigation.