Mixed Adsorbed Film of 2-(Octylsulfinyl)ethanol with Decylammonium Chloride at Water/Air Interface

Abstract

Abstract The surface tension of the aqueous solution of 2-(octylsulfinyl)ethanol and decylammonium chloride mixture has been measured by changing the total molality and composition of surfactants at 298.15 K under atmospheric pressure. It has been observed that the surface tension decreases with increasing the total molality at a constant composition and with decreasing the composition of decylammonium chloride at a constant total molality. Further the surface tension vs. total molality curve has been found to have a break point at a relatively low concentration. The thermodynamic equations have been developed so as to be applicable to the adsorption of nonionic–ionic mixture and used to calculate the surface density and the surface composition. It has been shown that the surface density vs. molality curve has the discontinuous change caused by the transition from a gaseous to an expanded film. By drawing the two-dimensional phase diagram and comparing it with the diagrams of the ionic–ionic surfactant mixtures, it has been proved that the shape of the phase diagram is affected greatly by the difference in the surface activity between the two surfactants.