Ionic micelle

The main peculiarity of solutions of reversed micelles is their ability to solubilize a wide class of ionic, polar, apolar, and amphiphilic substances. This is because in these systems a multiplicity of domains coexist apolar bulk solvent, the oriented alkyl chains of the surfactant, and the hydrophilic head group region of the reversed micelles. Ionic and polar substances are hosted in the micellar core, apolar substances are solubilized in the bulk apolar solvent, whereas amphiphilic substances are partitioned between the bulk apolar solvent and the domain comprising the alkyl chains and the surfactant polar heads, i.e., the so-called palisade layer [24],... 

From Eq. (13.3), it is clear that neutral molecules will have a net velocity. In normal electrophoresis, cations will migrate faster than neutrals, and neutrals will migrate faster than anions. Anions are electrophoretically migrating in a direction opposite to EOF. Separations of neutral molecules, such as organic explosives, can only be achieved by using buffer additives, such as micelles, ionic cyclodextrins, and bile salts. The interaction of neutral analytes with these ionic buffer additives results in a modified mobility that enables separation. 

An indirect indication of the presence of interactions between micellar phase and drugs is given by molecular and dynamic parameters of the drug and the micelles (ionic mobility, diffusion coefficient, hydrodynamic radius, apparent molecular mass), which are altered by the solubilization of lipophilic substances in a significant manner. 

The size of micelles. Ionic micelles suitable to solubilize natural hydrocarbons would have median diameters of about 60 A. 

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]. 

Small amounts of nonpolar compounds can dissolve in die nonpolar core of the micelle, ionic compounds are located in bulk water, and polar compounds can partition between the polar layer (Stem layer in ionic micelles. Figure 2.4) of the micelle and bulk water. The polar layer of the micelles formed by nonionic surfactants is larger than the Stem layer of the ionic micelles (Figure 2.12), In nonpolar solvents, water and polar solutes are located in the core of reverse micelles, and nonpolar solutes are dissolved in the nonpolar solvent (Figure 2.8). 

Second-order rate constant for hydrolysis in the absence of micelles, ionic strength I = 0.05 M Apparent sccond-ordcr rate constant for hydrolysis in the presence of CTAB micelles, 0.05M-NaOH and 2 x 10 M penicillin Apparent binding constant of penicillin derivative to micelle... 

For polar or charged solute components, reversed micelles, ionic interior with entrapped water molecules and a non-polar exterior, in an organic solvent mobile phase against a normal phase solid support is used. In this case, the solute molecules, such as nucleosides and amino acids, which normally would not be transported by an organic solvent, are mobilized by partitioning into the interior of the reversed micelle (12). 

Toullec, J., Couderc, S. Aqueous hexadecyltrimethylammonium acetate solutions pH and critical micelle concentration evidence for dependence of the degree of micelle ionic dissociation on acetate ion concentration. Langmuir 1997, 13(1), 1918-1924. 

The examples in the preceding section, of the flotation of lead and copper ores by xanthates, was one in which chemical forces predominated in the adsorption of the collector. Flotation processes have been applied to a number of other minerals that are either ionic in type, such as potassium chloride, or are insoluble oxides such as quartz and iron oxide, or ink pigments [needed to be removed in waste paper processing [92]]. In the case of quartz, surfactants such as alkyl amines are used, and the situation is complicated by micelle formation (see next section), which can also occur in the adsorbed layer [93, 94]. 

The ernes of ionic surfactants are usually depressed by tire addition of inert salts. Electrostatic repulsion between headgroups is screened by tire added electrolyte. This screening effectively makes tire surfactants more hydrophobic and tliis increased hydrophobicity induces micellization at lower concentrations. A linear free energy relationship expressing such a salt effect is given by ... 

The Kraft point (T ) is the temperature at which the erne of a surfactant equals the solubility. This is an important point in a temperature-solubility phase diagram. Below the surfactant cannot fonn micelles. Above the solubility increases with increasing temperature due to micelle fonnation. has been shown to follow linear empirical relationships for ionic and nonionic surfactants. One found [25] to apply for various ionic surfactants is ... 

Micelles can solubilize gases. It has been demonstrated [49] that the Laplace model gives a good description of such solubilization for the case of ionic micelles ... 

Surfactants are long-chain compounds containing a hydrophobic tail and an ionic head. In polar solvents the surfactants arrange themselves in a spherical structure known as a micelle in which the hydrophobic tails form the... 

Silicates in Solutions. The distribution of sdicate species in aqueous sodium sdicate solutions has long been of interest because of the wide variations in properties that these solutions exhibit with different moduli (23—25). Early work led to a dual-nature description of sdicates as solutions composed of hydroxide ions, sodium ions, coUoidal sdicic acid, and so-called crystaHoidal sdica (26). CrystaHoidal sdica was assumed to be analogous to the simple species then thought to be the components of crystalline sdicate compounds. These include charged aggregates of unit sdicate stmctures and sdica (ionic micelles), and weU-defined sdicate anions. 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

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