全氟丁基磺酸钠与辛基三乙基溴化铵的相互作用

通过测定辛基三乙基溴化铵(C8H17N(CH2CH3)3Br,C8NE)与全氟丁基磺酸钠(C4F9SO3Na,C4F)组成的不同混合比的碳氢-碳氟正负离子表面活性剂混合体系的表面张力,得到不同摩尔比时C8NE-C4F体系的临界胶束浓度(cmc)、cmc处的表面张力(γcmc)、总饱和吸附量、不同表面张力时表面吸附层的组成,利用Gibbs-Duhem方程求得cmc处的胶团组成。采用规则溶液理论计算了胶团中分子间相互作用参数(βm),并求得cmc以上的胶团组成。实验表明,C8NE-C4F复配体系的cmc远远小于单体系的cmc,这也体现在该体系的βm负值很大,胶团内分子相互作用很强。但是C4F与C8NE复配后γcmc较C4F单体系的变化幅度不是特别大(γcmc降低2～4mN/m),这是由于C8NE-C4F碳链的不对称性导致部分C8NE的碳链在溶液表面弯曲而覆盖了C4F端基CF3基团。表面吸附层中氟表面活性剂相对于本体溶液是富集的,即使对于C8NE大大过量的体系,表面吸附层组成也在等摩尔附近;对于C4F过量的体系,C4F在表面吸附层中的比例比溶液中的略高。随着表面张力的降低,表面吸附层的组成相对更偏向于氟表面活性剂。cmc处的胶团组成随着体系中C4F含量的增大偏向于形成显著富含C4F的胶团,对于C8NE大大过量的体系,胶团组成接近等摩尔。cmc之后的胶团组成接近等摩尔,主要归因于此时静电相互作用占主导,这和溶液配制过程中发现复配体系超过cmc一定浓度后就易生成沉淀的现象是相符的。

Interactions between Sodium Perfluorobutane Sulfonate and Octyltriethylammonium Bromide

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.