Ionic liquids micellization

Blesic, M., Marques, M.H., Plechkova, N.V., Seddon, K.R., Rebelo, L.RN., and Lopes, A., Self-aggregation of ionic liquids Micelle formation in aqueous solution. Green Chem., 9, 481-490, 2007. 

Self-aggregation of ionic liquids micelle formation in aqueous solution. Green Chem., 9,481-490. 

Adhikari A, Dey S, Das DK, Mandal U, Ghosh S, Bhattacharyya K (2008) Solvation dynamics in ionic liquid swollen P123 triblock copolymer micelle a femtosecond excitation wavelength dependence study. J Phys Chem B 112(20) 6350-6357... 

Free energy of micellization, 24 130 Free enzyme-catalyzed reactions ionic liquids in, 26 897-898 Free fatty acids, 70 802-804, 825-826 removal of, 70 807 as soap bar additives, 22 742-743 Free-flow agents, in sodium chloride (salt), 22 808... 

Anderson, J.L. et al.. Surfactant solvation effects and micelle formation in ionic liquids, Chem. Comm., 2444, 2003. 

Beyaz, A., Oh, W.S., and Reddy, V.R, Ionic liquids as modulators of the critical micelle concentration of sodium dodecyl sulfate. Colloids Surf. B, 35,119, 2004. 

In contrast to singlet oxygen, charged intermediates cannot penetrate ionic liquid-liquid interphases (ionic micelles or microemulsions) owing to charge repulsion or attraction [23]. Sensitizer and substrate solubilization in different phases may therefore be of interest for an improvement of chemical yield. 

For ionic surfactants micellization is surprisingly little affected by temperature considering that it is an aggregation process later we see that salt has a much stronger influence. Only if the solution is cooled below a certain temperature does the surfactant precipitate as hydrated crystals or a liquid crystalline phase (Fig. 12.4). This leads us to the Krafft temperature1 also called Krafft point [526]. The Krafft temperature is the point at which surfactant solubility equals the critical micelle concentration. Below the Krafft temperature the solubility is quite low and the solution appears to contain no micelles. Surfactants are usually significantly less effective in most applications below the Krafft temperature. Above the Krafft temperature, micelle formation becomes possible and the solubility increases rapidly. 

A schematic two-dimensional representation of an ionic spherical micelle is shown in Pig. 2. Typically such micelles have average radii of 12-30 A and contain 20-100 monomers. The hydrophobic part of the aggregate forms the core of the micelle which is liquid-paralRn-like in... 

FORMATION OF MICELLES AND LIQUID CRYSTALS IN IONIC LIQUIDS... 

Evans et al. also showed that the 1 1 mixture of BAN and (3, y-distearoyl-phos-photidylcholine (DSPC) gives a smectic A texture in the temperature range of 57.3 to 100°C [21]. This is the first notice of lyotropic lamellar liquid crystals formed in the ionic medium. Additionally, Seddon et al. [28] and Neve et al. [29] have described the long-chained A-alkylpyridinium or l-methyl-3-alkylimidazolium ions to display smectic liquid-crystalline phases above their melting points, when Cl or tetrachloro-metal anions like CoCl " and CuCl " are used as the counter ions. Lin et al. have also noted the liquid crystal behavior of 1-alkylimidazolium salts and the effect on the stereoselectivity of Diels-Alder reactions [30]. However, liquid crystals are classified as ionic liquid crystals (ILCs), and they are distinguished from liquid crystals that are dispersed in ionic liquids. Although the formation of micelles and liquid crystal phases in ionic liquids have been thus reported, there has been no mention of the self-assembly of developed nano-assemblies that are stably dispersed in ionic liquids. In the next section the formation of bilayer membranes and vesicles in ionic liquids is discussed. 

In this study we restrict our consideration by a class of ionic liquids that can be properly described based on the classical multicomponent models of charged and neutral particles. The simplest nontrivial example is a binary mixture of positive and negative particles disposed in a medium with dielectric constant e that is widely used for the description of molten salts [4-6], More complicated cases can be related to ionic solutions being neutral multicomponent systems formed by a solute of positive and negative ions immersed in a neutral solvent. This kind of systems widely varies in complexity [7], ranging from electrolyte solutions where cations and anions have a comparable size and charge, to highly asymmetric macromolecular ionic liquids in which macroions (polymers, micelles, proteins, etc) and microscopic counterions coexist. Thus, the importance of this system in many theoretical and applied fields is out of any doubt. 

Studies of fluorescence of probe molecules [30] in ionic liquids revealed red shifts which are characteristic of organized media with long-lived structures (micelles). The fluorescence of the ionic liquids themselves shows the same signs [31], This can also be an indication of glassy dynamics. 

Figure 4.34 Solubilisation of cellulose, (a) By Cd-tren (b) A -methylmorpholine A -oxide (c) fringe micelles formed in apparently simple solutions (d) ionic liquids capable of solubilising cellulose and other polysaccharides.

Due to the d3mamic nature and to the small micellization enthalpies (25), micelles and other aggregates of amphiphilic molecules are sensitive in shape and size to various additives. It has been known for a long time that the addition of salt to solutions of ionic spherical micelles induces the formation of rodlike aggregates (144), but also the solubilization of alcohols, alkanes, and aromatic liquids (36,145-147) has consequences on aggregation numbers and on shapes of micelles. 

Imidazolium ILs easily form micro-emulsions using different surfactants such as long-chain alcohols and the properties of the new micelle-ionic liquid soluhons can be explored in inverse gas chromatography processes [124]. Moreover, ILs have been used as run buffer additives in capillary electrophoresis [125] and as ultra-low-volatility liquid matrixes for matrix-assisted laser desorption/ionizahon mass spectrometry [126]. 

This book reviews reactions in which ionic liquids, fluorous media and supercritical CO2 are used, as these solvents are the most promising new types of green reaction media. Sufficient details are provided to allow researchers to explore the use of these solvents in specific reactions. Typical examples of reaction conditions and workup procedures are included at the end of each chapter to allow chemists to utilize these new technologies with confidence, and extensive references to the literature are listed. Other standard green reaction media such as water, ethanol, aqueous surfactant micelles and polymers, as well as solvent-free conditions, are outside the scope of this book. 

Ammonium salts are well-known cationic surfactants. These amphiphilic molecules aggregate in aqueous solution to micelles and at higher concentrations to lyotropic (typical member is CTAB, eetyltimethylammonium bromide) (or thermotropie) mesophases. Beside this ammonium salts are used as phase transfer catalysts and as ionic liquids (ILs) in synthesis of nanopartickle catalysts [70-74],... 

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