Self-Aggregation of New Alkylcarboxylate-Based Anionic Surface Active Ionic Liquids: Experimental and Theoretical Investigations

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• 作者：Ni Cheng ; Pengming Yu ; Tao Wang ; Xiang Sheng ; Yanhui Bi ; Yanjun Gong ; Li Yu
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：March 13, 2014
• 年：2014
• 卷：118
• 期：10
• 页码：2758-2768
• 全文大小：587K
• 年卷期：v.118,no.10(March 13, 2014)
• ISSN：1520-5207

文摘

Halogen-free and low-cost alkylcarboxylate-based anionic surface active ionic liquids (SAILs), namely, 1-butyl-3-methylimidazolium alkylcarboxylates ([C₄mim][C_nH_2n鈥?O₂], n = 8, 10, 12), were first synthesized through the neutralization of imidazolium hydroxide by alkylcarboxylic acids. A systematic study of their self-aggregation behavior in water was investigated by surface tension, electrical conductivity, steady-state fluorescence quenching, and ¹H NMR. The micellar properties of this series of SAILs in ethylammonium nitrate (EAN) were also studied by surface tensiometry for comparison. A set of surface active parameters and thermodynamic parameters of these compounds in water and EAN was obtained. Surface tension results show that the surface activity of [C₄mim][C_nH_2n鈥?O₂] in EAN is inferior to that in water. They exhibit a higher ability to aggregate in water than the traditional anionic surfactants, sodium alkylcarboxylates (SAC), and anionic SAILs, 1-butyl-3-methylimidazolium alkylsulfates ([C₄mim][C_nH_2n+1SO₄]) with the same hydrocarbon chain length. This demonstrates that the incorporation of carboxylate group and [C₄mim]⁺ cation favors micelle formation. To understand the discrepancy in the surface activity of alkylsulfate- and alkylcarboxylate-based SAILs, theoretical calculations were performed to give electrostatic potential of the corresponding anions. The higher surface activity of [C₄mim][C₁₂H₂₃O₂] mainly originates from the lower electronegativity of its anion. Density functional theory (DFT) calculations manifest that the interaction energy of binary combination SAILs鈥揈AN is larger than that of SAILs鈥揌₂O, implying the stronger interaction of the former. Consequently, it is more difficult for [C₄mim][C_nH_2n鈥?O₂] to self-aggregate in EAN than in H₂O. This work is expected to be of practical value for the environmentally friendly alkylcarboxylate-based SAILs in some potential applications, including nanomaterials synthesis and phase separation, among others.