Distribution coefficient micelle

The bile salts and their ability to form mixed micelles is discussed in some detail in order to foster a better understanding of their applications. It is highly important for the electrophoretic characterization of the micellar phase, and therefore for the calculation of the distribution coefficients, to have a thorough understanding of the mode of micelle formation and structural changes achieved by alteration of the surfactant concentration and micelle composition as well as to develop strategies for micelle optimization. 

In principle any ionic or neutral tenside could be used instead of the bile salts. For neutral tensides, the micelle would not have to be marked when the EOF is known. The distribution coefficients can be obtained from Eq. 

The cmc reduction degree of CyFNa by ROH is less than that of Cio SNa. The distribution coefficients of ROH between the micelle and the aqueous solution have a smaller value in the ROH-C FNa system. All these facts show the existence of "(tlutual phobicity" between FC and HC chains at the surface and in the micelles. 

Solubilizing Capacity of Surfactant Micelles and Distribution Coefficient of Timobesome Acetate in Aqueous Micellar Solutions at 25°C Solubilizing Capacity Distribution ... 

Enhanced HOC solubility in surfactant systems generally has been quantified by a distribution coefficient that only considers HOC partitioning to surfactant micelles that exist above the critical micelle concentration (CMC). Although surfactants can form a mobile micellar pseudophase that leads to the facilitated transport of solubilized HOCs, they also can be adsorbed by the solid matrix and thereby lead to HOC partitioning to immobile sorbed surfactants and, thus, enhanced HOC retardation. Therefore, the effectiveness of a remediation scheme utilizing surfactants depends on the distribution of an HOC between immobile compartments (e.g., subsurface solids, sorbed surfactants) and mobile compartments (e.g., water, micelles). 

Our results for HOC partitioning in the presence of sorbed surfactant and micelles demonstrate that large differences can exist in the HOC sorption capacity of surfactant aggregates in micellar versus sorbed forms. This can be seen quite readily by calculating Kss values as a function of surfactant dose from the experimental KD values. The distribution coefficient defines the HOC mass balance and can be expressed as ... 

The retention factor can be related to the distribution coefficient, K, between the micelle and aqueous phase by... 

The distribution coefficient, K, of a solute for an equilibrium between the aqueous phase and micelle, or the micellar solubilization, depends on temperature generally, the distribution coefficient decreases with an increase in temperature. This means that the migration time of a solute, will be reduced when the temperature is elevated under typical micellar electrokinetic chromatography (MEKC) conditions, where, for example, sodium dodecyl sulfate (SDS) is employed as a pseudo-stationary phase at a neutral condition (i.e., pH 7). Also, the velocity of the electro-osmotic flow (EOF), Meof> and the electrophoretic velocity of the micelle, (me), will be increased by an increase in temperature because of a reduced viscosity of the micellar solution employed in a MEKC system. 

Table 6.13 Micelle/water distribution coefficients, P, for the solubilisation of benzoic acid by r>olkyl polyoxyethylene surfactants C E , (where n = alkyl (C) chain length and m = polyoxyethylene (E) chain length) os a function of temperature°...

This equilibrium or partitioning of a solute between micelles and the aqueous surroundings has not been uniformly described in the literature. We speak of distribution coefficient or constant, partition coefficient or constant, or equilibrium constant to describe equilibria that are the same qualitiatively speaking. However, the definition of the above-mentioned coefficients or constants varies. In this chapter we refer to the process as a partitioning of a molecule between micelles and the aqueous surroundings, and we term it the partition coefficient regardless of the concentration units used to define it. 

It is also of considerable interest to look at concentration dependence from another angle by focusing on the fraction of alcohol solubilized by the micelles. If the distribution coefficient does not vary with surfactant concentration, it is obvious that the fraction of alcohol solubilized does, as demonstrated by Equation 6.8. Here, it is rearranged taking into account that the alcohol is at infinite dilution ... 

In developing distribution coefficients the activity coefficients of the solute in the micelle and in the aqueous environment have been neglected. The large decrease in observed as the alcohol content increases toward saturation indicates that the activity coefficients deviate significantly from unity as the alcohol content increases. 

Gao, Z., Wasylishen, R.E., and Kwak, J.C.T., An NMR paramagnetic relaxation method to determine distribution coefficients of solubilization in micellar systems, J. Phys. Chem., 93, 2190, 1989. Treiner, C., The partitioning of neutral solutes between micelles and water as deduced from critical micelle concentration determinations, in Solubilization in Surfactant Aggregates, Christian, S.D. and Scamehorn, J.R, Eds., Marcel Dekker, New York, 1995, chap. 12. 

Eq. (5.223) coincides with the monomer diffusion equation proposed by Evans et al. [149] if the rate constant Rb in [149] is replaced by c°[rc ,(c + a c, )]. However, the obtained result is not restricted to the interpretation of the coefficients only, which have been used before. Eq. (5.224) does not coincide with the corresponding diffusion equation in [149] even if we replace Rb by this expression. Unlike the equations derived in the preceding works, the system (5.223) and (5.224) takes into account the polydispersity of micelles and the two-step nature of the micellisation. Actually, the release or incorporation of monomers in the second step of disintegration or formation of micelles is determined not only by their transition from the micellar to the premicellar region and their subsequent disintegration (as characterised by the parameter J) but also by the alteration of the size distribution of micelles. The latter change... 

Three types of interaction mechanisms are known between the micelle and the analyte as shown in Figure 3.3 (1) incorporation of the analyte into the hydrophobic core, (2) adsorption of the analyte on the surface or on the palisade layer, and (3) incorporation of the analyte as a cosurfactant. Highly hydrophobic and nonpolar analytes such as aromatic hydrocarbons will be incorporated into the core of the micelle. The selectivity may not be very different among long alkyl-chain surfactants for this class of analyte but the distribution coefficient will be increased with longer alkyl-chain surfactants. Thus, selectivity will not be altered significantly for nonpolar hydrophobic analytes, even when different surfactants are used. However, bile salts may provide substantially different selectivity in comparison with long-alkyl chain surfactants, even for nonpolar hydrophobic analytes. 

The distribution coefficients of PAN and CAS indicators between microemulsion droplets and the water-continuous phase in O/W microemulsions constituted of anionic, cationic, and nonionic surfactants have been measured in order to investigate the mechanism of enhanced sensitivity of reactions in O/W microemulsion [31]. From Table 2 one can see that the distribution coefficients of PAN and CAS indicators in all O/W microemulsions are larger than those in micelles with the same surfactants. Thus, we can conclude from these results that the reason for higher sensitivity in microemulsions is that a microemulsion has greater solubilization capacity for indicators or complexes. 

As discussed, the major determinant of the distribution coefficient between the aqueous phase and the oil phase of relatively nonpolar lipids such as cholesterol is the concentration of lipolytic products in the aqueous phase, since the paraffin chains of the lipolytic products, forming the lipid core of the micelle, are responsible for its solvent capacity (23,73). Micelle formation and the associated appearance of new solvent properties result from a cooperative effect of bile acids and lipolytic products (Fig. 16). Bile acids alone aggregate to form micelles, but these micelles have extremely poor solvent properties. Lipolytic products alone form very large liquid crystalline aggregates which probably have excellent solvent properties for lipids. When mixed, micelles of intermediate size are formed. The size is sufficiently small to permit rapid diffusion, and the lipolytic products in the center of the micelle provide a core of liquid hydrocarbon with useful solvent properties. 

The adempts to rationalize GrifHn s HLB scale from a physicochemical point of view were made in a number of studies. Various correlations were shown to exist between the HLB numbers and the chemical structure or molecular composition of the siufactants. Correlations were also fotmd between the HLB number and physicochemical properties of surfactants and their solutions, for example, stffface and interfacial tension, solubility, and heat of solution, spreading and distribution coefficient, dielectric permittivity of the surfactant, cloud point and phase inversion point, critical micelle concenlration, foaminess, etc. These studies are reviewed in Ref. 262. However, the correlations found are not generally applicable moreover, the concept of the additivity of HLB numbers as such for mixtures of surfactants or oils cannot be proven expermentally when the surfactant characteristics are varied over a wider range (265). 

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