物理化学学报 >> 2009, Vol. 25 >> Issue (10): 2020-2025.doi: 10.3866/PKU.WHXB20091003

研究论文 上一篇    下一篇

光敏季铵盐Gemini表面活性剂a4-6-m在气/液界面的吸附

宋冰蕾, 赵剑曦   

  1. 福州大学化学化工学院应用化学系, 福州 350108
  • 收稿日期:2009-05-26 修回日期:2009-07-02 发布日期:2009-09-29
  • 通讯作者: 赵剑曦 E-mail:jxzhao.colloid@fzu.edu.cn

Adsorption of Photosensitive Quaternary Ammonium Gemini Surfactant a4-6-m at the Air/Water Interface

SONG Bing-Lei, ZHAO Jian-Xi   

  1. Department of Applied Chemistry, College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou 350108, P. R. China
  • Received:2009-05-26 Revised:2009-07-02 Published:2009-09-29
  • Contact: ZHAO Jian-Xi E-mail:jxzhao.colloid@fzu.edu.cn

摘要:

合成了3种不对称结构的季铵盐Gemini表面活性剂a4-6-m, 分子的一根疏水链是偶氮苯为端基的4个亚甲基链, 另一根是不同长度的脂肪链(m=12, 14, 16). 研究结果表明, 反式偶氮苯封端的a4-6-m在气/液界面上以直立方式排列, 偶氮苯端基间的π-π相互作用导致吸附分子较为紧密地排列, 但吸附层外表面含有偶氮苯成分使临界胶束浓度(cmc)时的表面张力(γcmc)较大. 紫外光激发使反式结构偶氮苯变为顺式结构, 这些极性较强的顺式偶氮苯夹杂在直立的烷烃链间, 增强的偶极-偶极相互作用促进了分子紧密排列, 使分子占据面积(Amin)略微减小. 增长脂肪链长度有助于降低临界胶团浓度和C20(使水的表面张力降低20 mN·m-1时所需的表面活性剂浓度), 但对γcmc影响不大.

关键词: 表面张力, 不对称光敏Gemini表面活性剂, 偶氮苯封端, 气/液界面吸附, 顺反异构

Abstract:

Three dissymmetric quaternary ammonium Gemini surfactants (referred to as a4-6-m) were synthesized. One of the two hydrophobic chains of a4-6-m was a butyl chain terminated by an azobenzene group and the other was a conventional aliphatic chain of different length (m=12, 14, 16). The results showed that the trans-a4-6-m molecules adsorbed at the air/water interface with a vertical orientation of the two hydrophobic chains. The π-π interaction between azobenzene groups resulted in a denser arrangement of the surfactants. The azobenzene groups toward the air-side in the adsorption layer yielded a higher γcmc (surface tension value corresponding to the critical micelle concentration (cmc)) by comparison to 12-6-12. After UV-light irradiation, the trans-azobenzene groups converted into twisted cis-forms with a large dipole moment. These cis-azobenzene groups lay among the vertically oriented aliphatic chains and their relatively free location enhanced their dipole-dipole interactions, which promoted the tight packing of adsorbed molecules and slightly reduced the minimummolecular occupation area (Amin). The increase in aliphatic chain length led to a reduction of the cmc and the C20 (concentration of surfactant required to reduce 20 mN·m-1 surface tension of water), but had little effect on the γcmc.

Key words: Surface tension, Dissymmetric photosensitive Gemini surfactant, Terminal azobenzene, Adsorption at air/water interface, trans-cis isomerization

MSC2000: 

  • O647