表面活性剂和四烷基溴化铵的复配 Ⅱ.四乙基溴化铵对离子型表面活性剂在气/液表面吸附行为的影响

Mixing of Surfactant and Tetraalkylammonium Bromide .Effect of Tetraethylammonium Bromide on the Adsorption ofJZ Ionic Surfactants at Air/Water Interface

用表面张力法研究了有机电解质四乙基溴化铵（（Ｅｔ）４ＮＢｒ）对离子型表面活性剂十二烷基硫酸钠（ＳＤＳ）和十二烷基三甲基溴化铵（ＤＴＡＢ）在气／液表面吸附行为的影响。表明（Ｅｔ）４ＮＢｒ提高了ＳＤＳ和ＤＴＡＢ降低水溶液表面张力的效率。但（Ｅｔ）４ＮＢｒ仅提高ＤＴＡＢ降低水溶液表面张力的能力，却反而削弱了ＳＤＳ降低水溶液表面张力的能力。通常电解质对离子表面活性剂表面吸附层的影响主要来自与表面活性离子电性相反的反离子，它们屏蔽了表面活性剂离子头基间的电荷，致使表面活性剂在气／液表面层排列紧密。有机电解质离子（Ｅｔ）４Ｎ＋作为反离子时，除了具有电解质离子的通常性能外，其乙基和表面活性剂碳氢链间还有一定程度的弱疏水相互作用，使部分（Ｅｔ）４Ｎ＋离子嵌入ＳＤＳ吸附层的离子头基区中，较大（Ｅｔ）４Ｎ＋离子的嵌入使周围的ＳＤＳ碳氢链排列疏松，改变了朝向空气面的表面碳氢链覆盖层结构，从而削弱了其降低表面张力的能力。

The effects of tetraethylammonium bromide (Et)4NBr on the adsorption of ionic surfactants (sodium dodecyl sulfate,SDS;and dodecyltrimethylammonium bromide,DTAB) at air/water interface have been examined using surface tension measurements.The results showed that (Et)4NBr enhanced the surface tension reduction efficiency of both SDS and DTAB,however,only enhanced DTAB but weakened SDS in the surface tension reduction effectiveness.In general,the electrolyte counterions corresponding to the surfactant are a main factor affecting the adsorption of ionic surfactant at air/water interface.These electrolyte counterions screen the ionic groups of surfactant,leading to their close packing at air/water interface.When (Et)4N+ as the counterions,besides electrostatic attraction with the oppositelycharged headgroups of surfactant,there is to a certain extent hydrophobic interaction between the ethyl groups of (Et)4N+ ions and the hydrocarbon chains of SDS.This leads some (Et)4N+ ions embedding into SDS adsorpti