Aggregation Behavior of Long-Chain N-Aryl Imidazolium Bromide in Aqueous Solution

The aggregation behavior of three long-chain N-aryl imidazolium ionic liquids (ILs), 1-(2,4,6-trimethylphenyl)-3-alkylimidazolium bromide [C n pim]Br (n = 10, 12, and 14), in aqueous solutions was systematically explored by surface tension, electrical conductivity, and 1H NMR. A lower critical micel...

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Bibliographic Details
Published in:Langmuir 2011-03, Vol.27 (5), p.1618-1625
Main Authors: Shi, Lijuan, Li, Na, Yan, Han, Gao, Yan’an, Zheng, Liqiang
Format: Article
Language:English
Subjects:
Chemistry
Colloidal state and disperse state
Colloids: Surfactants and Self-Assembly, Dispersions, Emulsions, Foams
Exact sciences and technology
General and physical chemistry
Micelles. Thin films
Photochemistry
Physical chemistry of induced reactions (with radiations, particles and ultrasonics)
Surface physical chemistry
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Summary:The aggregation behavior of three long-chain N-aryl imidazolium ionic liquids (ILs), 1-(2,4,6-trimethylphenyl)-3-alkylimidazolium bromide [C n pim]Br (n = 10, 12, and 14), in aqueous solutions was systematically explored by surface tension, electrical conductivity, and 1H NMR. A lower critical micelle concentration (cmc) for the N-aryl imidazolium ILs is observed compared with that for 1,3-dialkylimidazolium ILs [C n mim]Br, indicating that the incorporation of the 2,4,6-trimethylphenyl group into a headgroup favors micellization. The enhanced π−π interactions among the adjacent 2,4,6-trimethylphenyl groups weaken the steric hindrance of headgroups and thus lead to a dense arrangement of [C n pim]Br molecules at the air−water interface. An analysis of the 1H NMR spectra revealed that the introduced 2,4,6-trimethylphenyl group may slightly bend into the hydrophobic regions upon micellization. The micelle formation process for [C n pim]Br (n = 10, 12, and 14) was found to be enthalpy-driven in the investigated temperature range, which is attributed to the strong electrostatic self-repulsion of the headgroups and the counterions as well as the π−π interactions among headgroups. Strong, stable fluorescence properties are presented by the new N-aryl imidazolium ILs, indicating their potential application in the field of photochemistry.
ISSN:0743-7463
1520-5827
DOI:10.1021/la104719v