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Micellar Exchange Kinetics of Quaternary Ammonium Type Gemini Surfactants Monitored by NMR
maosz@wipm.ac.cn
Author NameAffiliationE-mail
maosz@wipm.ac.cn State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China maosz@wipm.ac.cn 
Abstract:
Dynamic NMR (DNMR) method was used to detect kinetic parameters of the micelle/monomer molecular exchange in aqueous solution 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 the escape rate constant (k-) for 14-s-14 and 12-s-12 are respectively 101 and 103 s-1, the apparent activation energies of escape of 14-s-14 and 12-s-12 are respectively 54.04-73.64 KJ/mol and 33.42-47.09 KJ/mol. Furthermore, the escape rate constant (k-) increased and the apparent activation energy of escape decreased with the spacer length growing. In combination with the micro-polarity measurements by the fluorescence probe experiment the involved two-step exchange mechanism of 14-s-14 and 12-s-12 are revealed.
Key words:  Gemini surfactants  dynamic NMR  molecular exchange  exchange rate constant  apparent activation energy  two-step exchange mechanism
FundProject:
Micellar Exchange Kinetics of Quaternary Ammonium Type Gemini Surfactants Monitored by NMR
maosz@wipm.ac.cn
摘要:
Dynamic NMR (DNMR) method was used to detect kinetic parameters of the micelle/monomer molecular exchange in aqueous solution 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 the escape rate constant (k-) for 14-s-14 and 12-s-12 are respectively 101 and 103 s-1, the apparent activation energies of escape of 14-s-14 and 12-s-12 are respectively 54.04-73.64 KJ/mol and 33.42-47.09 KJ/mol. Furthermore, the escape rate constant (k-) increased and the apparent activation energy of escape decreased with the spacer length growing. In combination with the micro-polarity measurements by the fluorescence probe experiment the involved two-step exchange mechanism of 14-s-14 and 12-s-12 are revealed.
关键词:  Gemini surfactants  dynamic NMR  molecular exchange  exchange rate constant  apparent activation energy  two-step exchange mechanism
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