Micelle formation of 1-alkyl-3-methylimidazolium bromide ionic liquids in aqueous solution (original) (raw)
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Aggregation and micelle formation of ionic liquids in aqueous solution
Chemical Physics Letters, 2004
Association of ionic liquids possessing n-octyl moiety either in the cation or in the anion has been studied in aqueous solution with conductivity and turbidity measurements as well as using 2-hydroxy-substituted Nile Red solvatochromic probe. 1-Butyl-3methylimidazolium octyl sulfate was found to act as a surfactant above 0.031 M critical micelle concentration. In contrast, 1-methyl-3-octylimidazolium chloride produced inhomogeneous solution of larger aggregates, which were dissolved on the addition of more than 2:1 molar excess of sodium dodecyl sulfate (SDS) due to mixed micelle formation. Even small amount (<10 mM) of ionic liquids could markedly reduce the polarity of the Stern layer of SDS micelle.
Micelle formation of imidazolium ionic liquids in aqueous solution
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2008
Ionic liquids (ILs) form a new class of compounds with a much varied industrial and technological application. Some research has been conducted in ecotoxicity of these compounds, but very little is known about their structure in aqueous solutions. It is known that some ionic liquids can form aggregates in aqueous solution. To determine how such structures influence the use, distribution and toxicity of ILs, first the critical micelle concentrations of the ILs need to be determined. Therefore the critical micelle concentration (CMC) for a number of imidazolium ionic liquids was determined in aqueous solution. The expected dependency of the CMC on the length of the alkyl chain of the investigated 1-alkyl-3-methylimidazolium ILs was shown. The degree of ionization and the energy of aggregation were calculated and related to the alkyl chain length of the imidazolium. A significant correlation between retention times in reversed phase gradient HPLC, and the pCMC was observed. It was also shown that the CMC is directly related to the lipophilicity of the cation.
Journal of Colloid and Interface Science, 2011
The impetus for the increasing interest in studying surface active ionic liquids (SAILs; ionic liquids with long-chain ''tails'') is the enormous potential for their applications, e.g., in nanotechnology and biomedicine. The progress in these fields rests on understanding the relationship between surfactant structure and solution properties, hence applications. This need has prompted us to extend our previous study on 1-(1-hexadecyl)-3-methylimidazolium chloride to 1-(1-alkyl)-3-methylimidazolium chlorides, with alkyl chains containing 10, 12, and 14 carbons. In addition to investigating relevant micellar properties, we have compared the solution properties of the imidazolium-based surfactants with: 1-(1-alkyl)pyridinium chlorides, and benzyl (2-acylaminoethyl)dimethylammonium chlorides. The former series carries a heterocyclic ring head-group, but does not possess a hydrogen that is as acidic as H2 of the imidazolium ring. The latter series carries an aromatic ring, a quaternary nitrogen and (a hydrogen-bond forming) amide group. The properties of the imidazolium and pyridinium surfactants were determined in the temperature range from 15 to 75°C. The techniques employed were conductivity, isothermal titration calorimetry, and static light scattering. The results showed the important effects of the interactions in the interfacial region on the micellar properties over the temperature range studied.
Journal of Colloid and Interface Science, 2007
A series of surface-active ionic liquids, RMeImCl, has been synthesized by the reaction of purified 1-methylimidazole and 1-chloroalkanes, RCl, R = C 10 , C 12 , C 14 , and C 16 , respectively. Adsorption and aggregation of these surfactants in water have been studied by surface tension measurement. Additionally, solution conductivity, electromotive force, fluorescence quenching of micelle-solubilized pyrene, and static light scattering have been employed to investigate micelle formation. The following changes resulted from an increase in the length of R: an increase of micelle aggregation number; a decrease of: minimum area/surfactant molecule at solution/air interface; critical micelle concentration, and degree of counter-ion dissociation. Theoretically-calculated aggregation numbers and those based on quenching of pyrene are in good agreement. Gibbs free energies of adsorption at solution/air interface, G 0 ads , and micelle formation in water, G 0 mic , were calculated, and compared to those of three surfactant series, alkylpyridinium chlorides, RPyCl, alkylbenzyldimethylammonium chlorides, RBzMe 2 Cl, and benzyl(3-acylaminoethyl)dimethylammonium chlorides, R AEtBzMe 2 Cl, respectively. Contributions to the above-mentioned Gibbs free energies from surfactant methylene groups (in the hydrophobic tail) and the head-group were calculated. For RMeImCl, the former energy is similar to that of other cationic surfactants. The corresponding free energy contribution of the head-group to G 0 mic showed the following order: RPyCl ≈ RBzMe 2 Cl > RMeImCl > R AEtBzMe 2 Cl. The head-groups of the first two surfactant series are more hydrophobic than the imidazolium ring of RMeImCl, this should favor their aggregation. Micellization of RMeImCl, however, is driven by a relatively strong hydrogen-bonding between the chloride ion and the hydrogens in the imidazolium ring, in particular the relatively acidic H2. This interaction more than compensates for the relative hydrophilic character of the diazolium ring. As indicated by the corresponding G 0 mic , micellization of R AEtBzMe 2 Cl is more favorable than that of RMeImCl because the-CONH-group of the former surfactant series forms hydrogen bonds to both the counter-ion and the neighboring molecules in the micelle.
Thermodynamics of micellization of imidazolium ionic liquids in aqueous solutions
Journal of Colloid and Interface Science, 2009
The structural similarity between some ionic liquids (ILs) and ionic surfactants, indicates that ILs are expected to exhibit surface adsorption and aggregation properties. The Krafft temperature and the temperature dependence of the critical micelle concentration (CMC) were determined for four imidazolium ionic liquids with varying chain length by measuring concentration dependence of electrical conductivity at different temperatures. The magnitude of the thermodynamic parameters of the micelle formation provide valuable information about the driving force of micellization of these compounds, therefore, the parameters of these chemicals were estimated from the degree of ionization, and the CMC. The thermodynamic parameters were correlated to directly measured values using isothermal titration calorimetry (ITC). It was found that the long-chained imidazolium ILs show similar thermodynamic characteristics as traditional cationic surfactants, whereas the Krafft temperature was shown to be lower than that of traditional cationic surfactants of similar chain length.
Journal of Colloid and Interface Science, 2010
The complex formation between anionic polyelectrolyte poly(acrylic acid sodium salt) [NaPAA] and surface active ionic liquid (SAIL) lauryl isoquinolinium bromide [C 12 iQuin][Br] in aqueous media has been investigated by surface tension, isothermal titration calorimetry (ITC), and conductance. The self-assembled structures have been characterized using dynamic light scattering (DLS) and turbidity measurements. A range of surface parameters have been calculated from tensiometric measurements including critical micelle concentration (CMC), surface excess concentration (Γ cmc), surface pressure at the interface (Π cmc), minimum area occupied at air-solvent interface (A min), adsorption efficiency (pC 20), and surface tension at the CMC (γ cmc). The thermodynamic parameters, i.e., standard enthalpy of micellization ΔH m À Á , standard free energy of micellization (ΔG m), and standard entropy of micellization (ΔS m) have also been evaluated. Four different stages of transitions, corresponding to the progressive formation of NaPAA-[C 12 iQuin][Br] complex (C 1) , critical aggregation concentration (CAC), critical saturation concentration (C 3) and CMC have been observed owing to strong electrostatic and hydrophobic interactions. The results obtained from DLS and turbidity measurements show that size of the aggregates first decreases and then increases in the presence of polyelectrolyte. The binding isotherms obtained using isothermal titration calorimetry (ITC) show the concentration dependence as well as the highly cooperative nature of interactions corresponding to formation of polyelectrolyte-SAIL complexes.
Journal of Dispersion Science and Technology, 2019
Two surface active ionic liquids (ILs) having 1-alkyl-3-methylimidazolium cationic moiety and dodecylbenzenesulfonate based anionic moiety i.e. [C 5 mim][DBS] and [C 7 mim][DBS], have been synthesized. 1 H-NMR, thin layer chromatography were done for their characterization. These DBS-ILs have lower critical micelle concentration (CMC) in comparison with their conventional sodium dodecylbenzenesulfonate [Na][DBS] surfactants and hence are highly surface active. The conductance, surface tension, absorption (UV-visible) and emission (Fluorescence) techniques were used to determine the CMC values. DBS-ILs showed a remarkable absorption and emission spectra where intensity changes with variation in concentration of IL. Micelle self-assembly formation was also predicted by dynamic light scattering (DLS) technique. Conductance and surface tension techniques were employed to study the aggregation behavior in aqueous conditions. Various surface active parameters were evaluated at 298.15 K employing surface tension techniques. Conductance measurements were performed at three rising temperatures (288.15, 298.15, and 308.15) K and their thermodynamic parameters were calculated. From the above studies, the present synthesized ionic liquids found to have remarkable surface activity.