On the Self-Aggregation and Fluorescence Quenching Aptitude of Surfactant Ionic Liquids

Instituto de Tecnologia Quimica e Biologica, ITQB 2, Universidade Nova de Lisboa, Apartado 127, 2780-901 Oeiras, Portugal.
The Journal of Physical Chemistry B (Impact Factor: 3.3). 08/2008; 112(29):8645-50. DOI: 10.1021/jp802179j
Source: PubMed


The aggregation behavior in aqueous solution of a number of ionic liquids was investigated at ambient conditions by using three techniques: fluorescence, interfacial tension, and (1)H NMR spectroscopy. For the first time, the fluorescence quenching effect has been used for the determination of critical micelle concentrations. This study focuses on the following ionic liquids: [Cnmpy]Cl (1-alkyl-3-methylpyridinium chlorides) with different linear alkyl chain lengths (n=4, 10, 12, 14, 16, or 18), [C12mpip]Br (1-dodecyl-1-methylpiperidinium bromide), [C12mpy]Br (1-dodecyl-3-methylpyridinium bromide), and [C12mpyrr]Br (1-dodecyl-1-methylpyrrolidinium bromide). Both the influence of the alkyl side-chain length and the type of ring in the cation (head) on the CMC were investigated. A comparison of the self-aggregation behavior of ionic liquids based on 1-alkyl-3-methylpyridinium and 1-alkyl-3-methylpyridinium cations is provided. It was observed that 1-alkyl-3-methylpyridinium ionic liquids could be used as quenchers for some fluorescence probes (fluorophores). As a consequence, a simple and convenient method to probe early evidence of aggregate formation was established.

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Available from: Jose Nuno A Canongia Lopes
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    • "In recent years, SAILs with diverse cation, such as imidazolium, pyridinium, and piperidinium, have been widely researched [14] [15] [16] [17]. "
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    ABSTRACT: Specific effects of m- and p-hydroxybenzoate anions (m-HB and p-HB) as counterion on the aggregation process of surface active ionic liquids based on 1-dodecyl-3-methylimidazolium were investigated by surface tension, conductivity and steady state fluorescence measurements. Compared to that for 1-dodecyl-3-methylimidazolium bromide (C12mimBr), lower critical micelle concentration (cmc) and larger Πcmc and pC20 values for these SAILs indicate that the introduction of aromatous counterions favors micellization and reduction of surface tension. The most incorporated salicylate anion can effectively screen electrostatic repulsion, promoting a closer arrangement of C12mimSal at air–solution interface. Thus m- and p-C12mimHB have smaller Γmax and larger Amin values than C12mimSal. From the results of conductivity measurements, the cmc values of these SAILs increase slightly with increasing temperature, which has similar trend with cationic SAIL, 1-alkyl-3-methylimidazolium bromide, [Cnmim]Br. The negative ΔGmθ values, mainly result from more negative-T ΔSmθ, reveal that the micellization process is spontaneous and entropy-driven in the whole studied temperature range. The data also show that ΔHmθ values of all systems are negative, which implies that the micellization process is exothermic. This work suggests that small changes, such as position of the substitute on aromatic ring of counterion, can considerably influence the micellization behavior of SAILs.
    Full-text · Article · Apr 2015 · Journal of Molecular Liquids
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    • "Aggregationinduced conformational changes in different ILs were shown to depend on the aromatic ring, alkyl chain, counterions, and their interactions with water. Fluorescence quenching method in which pyridinium ILs acted as quenchers was firstly used to detect the aggregation behavior of surfactant ILs (Blesic et al., 2008). "

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    ABSTRACT: This paper deals with the synthesis and self-aggregation of a hydroxyl-functionalized imidazolium-based ionic liquid (IL) surfactant, namely 1-hydroxyethyl-3-dodecylimidazolium chloride ([C2OHC12im]Cl). The molecular structure was confirmed by means of electrospray ionization mass spectrometry (ESI–MS), 1H nuclear magnetic resonance (1H NMR) and elemental analysis. Many important physicochemical parameters, such as the critical micelle concentration (CMC), the surface tension at CMC (γCMC), the adsorption efficiency (pC 20), the surface pressure at CMC (ΠCMC), the maximum surface excess (Γ m ), the minimum molecular cross-sectional area (A min), the value of CMC/C 20, the average number of aggregation (N m ) and the micellar microenvironment polarity were determined by surface tension-concentration curves, fluorescence spectra, and electrical conductivity. The phenomena of the second CMC, the concentration dependence of N m , and the critical average aggregation number (N m,c) of imidazolium-based IL surfactants are reported for the first time in this paper. KeywordsHydroxyl-functionalized–Imidazolium-based–Ionic liquid surfactant–The second CMC–The critical aggregation number
    No preview · Article · Apr 2010 · Journal of Surfactants and Detergents
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