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Probing Dynamics and Mechanism of Exchange Process of Quaternary Ammonium Dimeric Surfactants, 14-s-14, in the Presence of Conventional Surfactants B
- Liu, Jun, Jiang, Yan, Chen, Hong, Mao, Shi Zhen, Du, You Ru, Liu, Mai Li
- The Journal of physical chemistry 2012 v.116 no.51 pp. 14859-14868
- ammonium, cationic surfactants, electrostatic interactions, fluorescence, hydrophobic bonding, micelles, nonionic surfactants, nuclear magnetic resonance spectroscopy, octoxynol, sodium dodecyl sulfate
- In this Article, we investigated effects of different types of conventional surfactants on exchange dynamics of quaternary ammonium dimeric surfactants, with chemical formula C₁₄H₂₉N⁺(CH₃)₂– (CH₂)ₛ–N⁺(CH₃)₂C₁₄H₂₉·2Br–, or 14-s-14 for short. Two nonionic surfactants, TritonX-100 (TX-100) and polyethylene glycol (23) laurylether (Brij-35), and one cationic surfactant, n-tetradecyltrimethyl ammonium bromide (TTAB), and one ionic surfactant, sodium dodecyl sulfate (SDS) were chosen as typical conventional surfactants. Exchange rates of 14-s-14 (s = 2, 3, and 4) between the micelle form and monomer in solution were detected by two NMR methods: one-dimensional (1D) line shape analysis and two-dimensional (2D) exchange spectroscopy (EXSY). Results show that the nonionic surfactants (TX-100 and Brij-35), the cationic surfactant (TTAB), and the ionic surfactant (SDS) respectively accelerated, barely influenced, and slowed the exchange rate of 14-s-14. The effect mechanism was investigated by the self-diffusion experiment, relaxation time measurements (T₂/T₁), the fluorescence experiment (I₁/I₃) and observed chemical shift variations. Results reveal that, nonionic conventional surfactants (TX-100 and Brij-35) loosened the molecule arrangement and decreased hydrophobic interactions in the micelle, and thus accelerated the exchange rate of 14-s-14. The cationic conventional surfactant (TTAB) barely changed the molecule arrangement and thus barely influenced the exchange rate of 14-s-14. The ionic conventional surfactant (SDS) introduced the electrostatic attraction effect, tightened the molecule arrangement, and increased hydrophobic interactions in the micelle, and thus slowed down the exchange rate of 14-s-14. Additionally, the two-step exchange mechanism of 14-s-14 in the mixed solution was revealed through interesting variation tendencies of exchange rates of 14-s-14.