Thermodynamic studies on adsorption at interfaces. III. Sodium dodecyl sulfate at water/hexane interface

The thermodynamic treatment of adsorption developed in Part I has been extended so as to include the case of strong electrolytes. By applying the thermodynamic relations to experimental results obtained for the system consisting of aqueous solution of sodium dodecyl sulfate (SDS) and hexane, the thermodynamic quantities of interface formation and partial molar quantities of the adsorption have been evaluated. Their values have been compared with the corresponding ones of tetradecanol described in Part II. It has been observed that SDS has a negative entropy of interface formation which is smaller than tetradecanol, while it has a larger interfacial concentration. This value is closely related to a larger positive value of the volume of interface formation. The above view has been confirmed by changes in the mean partial molar entropy and volume at adsorption. It has also been found from the energy of interface formation and partial molar energy of the adsorption that the adsorption of SDS from aqueous solution is inferior energetically to that of tetradecanol from hexane solution.