The surface tension of the aqueous solution of 1-octanol and 2-(octylsulfinyl)ethanol (OSE) mixture was measured as a function of the total molality of surfactants and the composition of OSE in the total surfactants at 298.15 K under atmospheric pressure. It was observed that 1-octanol molecules form mixed micelles with OSE molecules in the composition range above 0.850. The corresponding composition in the mixed adsorbed film was evaluated numerically by applying the thermodynamic relations developed previously. It was found that the surfactant molecules mix with each other in all proportions in the adsorbed film and the composition in the adsorbed film is smaller than that in the solution. Further, the adsorbed film was found to be richer in 1-octanol than the micelle at the critical micelle concentration (cmc). This behavior was attributed to the fact that 1-octanol is more surface active than OSE though it does not form the micelle.
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