反离子对氟表面活性剂的影响1. 表面活性及胶团化作用

通过表面张力和荧光探针法研究了全氟辛酸钠、全氟辛酸铵以及全氟辛酸四烷基铵[C₇F₁₅COON(C_nH_2n+1)₄, n＝1, 2, 3, 4]的表面活性以及胶团化作用, 系统地讨论了各种反离子, 特别是反离子大小的影响. 结果表明, 与普通碳氢表面活性剂不同, 反离子对这类氟表面活性剂的表面活性以及胶团化作用有很大影响. 表面活性剂的临界胶束浓度(cmc)随反离子的增大而下降; 饱和吸附层中平均每个分子所占的面积则大致随反离子的增大而增大. 而表面张力的变化则较为复杂. cmc时的表面张力随反离子的增大先上升(从全氟辛酸铵到全氟辛酸四乙铵)后下降(从全氟辛酸四乙铵到全氟辛酸四丁铵). 通过反离子的空间位阻、疏水性、插入以及电荷屏蔽效应对上述结果做了解释.

Effect of Counterions on Fluorinated Surfactants

The surface activity and micellization of sodium perfluorooctanoate, ammounium perfluoro- octanoate and tetraalkylammonium perfluorooctanoate [C7F15COON(CnH2 +) ,n=1,2,3,4] have been studied by n 1 4 surface tension and fluorescence methods. The effects of counterions, especially counterion size, on those fluorinated surfactants have been discussed. It is shown that, different from the nature of common hydrocarbon surfactants, the counterions has a striking effect on these fluorinated surfactants. The cmc of the fluorinated surfactants decreased with the increase of the counterion size, while the surface area per surfactant molecule in the air-water interface increased generally with the counterion size. However, the surface tension is more complicated. The surface tension at cmc first increases from C7F15COONH4 to C7F15COON(C2H5)4 and then decreases with the increase of counterion size. It was considered that the steric hindrance, hydrophobicity, electric screen, and penetration of the counterions may be responsible for the results.