文献类型：期刊文献

英文题名：Influence of Spacer of Gemini on the Interactions between Cationic Gemini Surfactant and Stearic Acid in Mixed Monolayers

作者：Li, Rong;Chen, Qibin[1];Liu, Honglai;Hu, Ying

机构：[1]E China Univ Sci & Technol, Adv Mat Lab, Shanghai 200237, Peoples R China; E China Univ Sci & Technol, Dept Chem, Shanghai 200237, Peoples R China

年份：2010

卷号：26

期号：12

起止页码：9342

外文期刊名：LANGMUIR

收录：;EI(收录号：20111913964596);WOS:【SCI-EXPANDED(收录号:WOS:000278427600028)】；

基金：This work is supported by the National Natural Science Foundation of China (No. 20736002, 20806025), Program for Changjiang Scholars and Innovative Research Team in University of China (No. IRT0721) and the 111 Project of China (No. B08021).

语种：英文

外文关键词：Isotherms - Phase separation - Gibbs free energy - Langmuir Blodgett films - Stearic acid - Monolayers

摘要：Mixed Langmuir-Blodgett (LB) films composed of a cationic gemini surfactant, [C18H37(CH3)(2)N+-(CH2)(s)-N+(CH3)(2)C18H37],2Br(-) (18-s-18 with s = 3, 6, 8, 10 and 12), and a fatty acid of stearic acid (SA) were studied by the pi-A isotherm measurement, as well as by AFM and FT-IR. The analysis of the mean molecular area, the excess area and the excess Gibbs free energy from pi-A isotherms suggests the existence of attractive interactions between 18-s-18 and SA molecules in the mixed monolayers. The spacer group of 18-s-18 plays a very important role in the surface properties of 18-s-18/SA mixed monolayers. When s <= 8, 18-s-18 and SA are completely miscible, while partially miscible mixed monolayers are presented when s > 8. Especially, in the latter case, when s = 12, phase separation appears in two composition regions of X-SA = 0.4-0.75 and X-SA = 0.75-0.85, respectively. This miscible phenomenon is confirmed by AFM observation. The result of FT-IR indicates that when X-SA <= 0.67, SA could ionize completely and form a "cationic-anionic surfactant" with 18-s-18 owing to the electrostatic interaction between the head groups, while when X-SA > 0.67, SA only partially ionizes, -COO- and -COOH coexist in mixed monolayers.