Miscibility of 1-hexanol and 2-(octylsulfinyl) ethanol in the adsorbed film and micelle

The surface tension of the aqueous solution of a 1-hexanol and 2-(octylsulfinyl)ethanol (OSE) mixture was measured as a function of the total concentration of 1-hexanol and OSE and the mole fraction of OSE in the total surfactant, The total surface density of 1-hexanol and OSE and the compositions in the adsorbed film and micelle were obtained by applying the thermodynamic equations, The phase diagrams analogous to those of binary mixtures were drawn for the adsorption and micelle formation. 1-Hexanol and OSE molecules were found to be miscible with each other in all proportions in the adsorbed film and partially in the micelle, Both the adsorbed film and micelle were richer in OSE than the solution, A great discrepancy in composition was observed between the adsorbed film and micelle coexisting in equilibrium at the critical micelle concentration, The discrepancy was ascribed to the large difference in size and property of head group, Further, a negative deviation from the ideal mixing was found in the adsorbed film, The large negative value of the excess Gibbs free energy was observed over the whole range of composition of the adsorbed film, which was attributed to a large attractive interaction between 1-hexanol and OSE molecules in the adsorbed film. (C) 1996 academic Press, Inc.