Micellar Exchange Kinetics of Quaternary Ammonium Type Gemini Surfactants Monitored by Nuclear Magnetic Resonance |
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| Authors: | Jun Liu You-ru Du Shi-zhen Mao Mai-li Liu |
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| Affiliation: | a.State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, Chinab.National Engineering Laboratory of Wheat & Corn Further Processing, Henan University of Technology, Zhengzhou 450000, China |
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| Abstract: | The dynamic NMR (DNMR) method was used to detect kinetic parameters of the molecular exchange process between monomers in bulk solution and those in the micelle for Gemini surfactants, 12-s-12 and 14-s-14(s=2, 3 and 4).The escape rate constant, k-, was derived based on the simplified equations of DNMR theory, and the apparent activation energy of escape, Ea-, was obtained based on the Arrhenius equation through temperature variation experiments.Results show that the orders of magnitude of k- for 14-s-14 and 12-s-12 are respectively 10 and 103 s-1, Ea- of 14-s-14 and 12-s-12 are respectively 54.04-73.64 and 33.42-47.09 kJ/mol.Furthermore, increases and Ea- decreases with the spacer length growing.In combination with the micro-polarity measurements, it was revealed that molecules of 14-s-14 and 12-s-12 have to experience conformation changes when escaping from the micelles.The two-step molecular exchange mechanism for Gemini surfactants was therefore supported. |
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| Keywords: | Gemini surfactants Dynamic nuclear magnetic resonance Molecular exchange Exchange rate constant Apparent activation energy Two-step exchange mechanism |
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