NMR Investigation of the Exchange Kinetics of Quaternary Ammonium Dimeric Surfactants C14-s-C14·2Br

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• 作者：Xiaohong Cui ; Xiaoyan Yang ; Hong Chen ; Ai-hong Liu ; Shizhen Mao ; Maili Liu ; Hanzhen Yuan ; Pingya Luo ; Youru Du
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：March 13, 2008
• 年：2008
• 卷：112
• 期：10
• 页码：2874 - 2879
• 全文大小：127K
• 年卷期：v.112,no.10(March 13, 2008)
• ISSN：1520-5207

文摘

The exchange kinetics of cationic gemini surfactants of the alkanediyl---bis(tetradecyldimethylammoniumbromide) type, with alkanediyl being 1,2-ethylene, 1,3-propylene, and 1,4-butylene, were investigated by ¹HNMR, 2D COSY, and 2D EXSY experiments. In contrast to the conventional surfactants, a second set ofwell-resolved resonance peaks appeared in the ¹H NMR spectra of these surfactants when their concentrationsreached their critical concentrations. These two sets of resonance peaks originate from their monomers andmicelles, which are proved by the correlation in the 2D COSY experiments and the cross polarization in the2D NOESY spectra. Therefore, exchanges between monomers in the bulk solution and in the micelles orother aggregates of this series of surfactants occur slowly on the NMR time scale. The exchange rate constantswere obtained by both NMR line shape analysis and 2D EXSY experiments, which are very consistent witheach other. The exchange rate constants for the gemini surfactants were found to be orders of magnitude lessthan those for the conventional single surfactants, and for geminis 14-s-14, the shorter the spacer, the slowerthe exchange dynamic. It still has been found that the fast exchange between monomers in the bulk solutionand in the micelles for gemini surfactant 12-2-12 at 25 C occurs slowly at 5 C on the NMR time scale.