The surface tension of the aqueous solution of 2-(octylsulfinyl)ethanol (OSE) and decylammonium chloride (DeAC) mixture was measured as a function of total molality and composition of surfactants at 298.15 K under atmospheric pressure. The total surface density and compositions in the adsorbed film and micelle of the mixture were evaluated by applying thermodynamic relations to experimental results. It was found that the phase diagrams obtained for the adsorption and micelle formation of the mixture are different in shape from those of 2-(decylsulfinyl)ethanol (DeSE)-OSE and dodecylammonium chloride (DAC)-DeAC mixtures which are assumed to mix ideally in the adsorbed film and micelle. Such a nonideal behavior was attributed to the attractive interaction between OSE and DeAC molecules. Further, the interaction is concluded to be more attractive in the micelle than in the adsorbed film.
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