Abstract:

The surface tension of the mixtures of cationic-anionic hydrocarbonfluorocarbon surfactants composed of octyltriethylammonium bromide(C8H17N(CH2CH3)3Br, C8NE) and sodium perfluorobutane sulfonate(C4F9SO3Na, C4F) with different molar ratios was measured. The cmc, γcmc, total adsorption amount, the compositions of surface adsorption layers at different surface tension values and the micell composition at cmc calculated by means of Gibbs-Duhem equation were obtained. The molecular interaction parameter βm and the micell composition after cmc were estimated via the regular solution theory. It shows that the cmc of each of C8NE-C4F mixtures was far smaller than that of individual component, which is consistent with the large negative value of βm and thus there are strong molecular interactions in micelle. However, the γcmc values of C8NE-C4F mixtures were not changed greatly as expected when compared with single C4F(γcmc was decreased by 2~4 mN/m), which might be attributed to the asymmetry between C8NE-C4F chains and some C8NE chains partially bending and covering the terminal CF3 group of C4F on the surface. In the surface adsorption layer, the fluorocarbon surfactant was rich-collected compared with the bulk solution. Even for those systems with C8NE in greatly excess, the composition of surface adsorption layer was just around equimolar; while for those systems with C4F in excess, the content of C4F in the surface adsorption layer was a little larger than that in solution. The composition of surface adsorption layer moved further to the C4F side with the decrease of surface tension. The micell composition at cmc was favorable to the formation of C4F-richer micelle with the increase of C4F content in bulk systems. For those systems with C8NE in great excess, the micell composition at cmc was around equimolar. The micell composition after cmc was approximately equimolar, which might be due to the predominant electrostatic interactions. It is consistent with the phenomenon that the mixture tended to precipitate when the concentration exceeded a certain amount after cmc.

Key words: Interactions between Sodium Perfluorobutane Sulfonate and Octyltriethylammonium Bromide