Abstract:The surface tension of the mixtures of cationic-anionic hydrogenated-fluorinated surfactants composed of octyltriethylammonium bromide (C8H17N(CH2CH3)3Br, C8NE) and sodium tetrafluoroethylene pentamer-oxylbenzenesulfonate (C10F19OC6H4SO3Na, 6201) with different molar ratios was measured. The critical micelle concentration (cmc), the minimum surface tension (γcmc), total amount adsorbed, the composition of surface adsorbed layer at different surface tension values and the micelle composition at cmc calculated by Gibbs-Duhem equation were obtained. The molecular interaction parameter βm and the micelle composition after cmc were estimated by the regular solution theory. It showed that, the cmc of C8NE-6201 mixtures was significantly smaller than that of individual component, which was also consistent with the large negative value of βm and thus the strong molecular interactions in micelles. However, the γcmc of C8NE-6201 mixtures were changed very small compared with single 6201, which might be attributed to the long hydrophobic chain of 6201 and the solubility was decreased when C8NE coexisted. Because of its strong hydrophobicity, 6201 primarily comprised the surface adsorbed layer and the micelle that were initially formed, while oppositely-charged C8NE offered the effect of synergism. The micelle composition after cmc, x6201m (the molar fraction of 6201 in micelle), however, maintained approximately in the range 0.6~0.7, indicating that cationic-anionic electrostatic interaction was the major role in micelle formation after cmc.
