Multiple Responsive Fluids Based on Vesicle to Wormlike Micelle Transitions by Single-Tailed Pyrrolidone Surfactants

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• 作者：Zan Jiang ; Kangle Jia ; Xiong Liu ; Jinfeng Dong ; Xuefeng Li
• 刊名：Langmuir
• 出版年：2015
• 出版时间：November 3, 2015
• 年：2015
• 卷：31
• 期：43
• 页码：11760-11768
• 全文大小：607K
• ISSN：1520-5827

文摘

We report a new family of multiple responsive fluids based on the single-tailed pyrrolidone surfactants, N-ethyl-2-pyrrolidone N-alkyl amine (C_mNP, where m = 10, 12, 14, 16, and 18). These surfactants are highly sensitive to solution pH as a result of the presence of the N-amino group in the molecules. Equilibrium surface tension results indicate that both the surface activity and micellization ability of C_mNPs decrease with the increase of the protonation degree; i.e., they exhibit a higher critical micelle concentration (cmc) and higher surface tension at the cmc (纬_cmc) at the acidic conditions than those at the basic conditions. The cmc values of C_mNPs follow the well-known Klevens equation, which decrease linearly with the increase of the hydrocarbon chain length m at a given pH. More importantly, the self-assemblies of C_mNPs are highly sensitive to pH, CO₂, and CuCl₂, as identified by turbidity and viscosity. The transitions between vesicles and wormlike micelles are further confirmed by rheology, static and dynamic light scattering (SLS and DLS), cryogenic transmission electron microscopy (cryo-TEM), and nuclear magnetic resonance (NMR) techniques systematically. Although the aggregate transitions induced by different factors are similar, however, the mechanisms are different. The pH- and CO₂-induced transitions are attributed to variation in the protonation degree of the N-amino group; however, CuCl₂-induced transitions are a result of the formation of C_mNP and CuCl₂ coordination complexes as revealed by two-dimensional (2D) nuclear Overhauser effect spectrometry (NOESY) NMR and ultraviolet鈥搗isible (UV鈥搗is) spectra.