Micelles, partition into

When using an alcohol/surfactant solution to modify the density of DNAPLs, several processes occur simultaneously (Figure 2). Perhaps the most important process is alcohol partitioning, where alcohol which is initially solubilized in surfactant micelles partitions into the DNAPL,... 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

A form of capillary electrophoresis in which neutral solutes are separated based on their ability to partition into a charged micelle. 

The elution order for neutral species in MEKC depends on the extent to which they partition into the micelles. Hydrophilic neutrals are insoluble in the micelle s hydrophobic inner environment and elute as a single band as they would in CZE. Neutral solutes that are extremely hydrophobic are completely soluble in the micelle, eluting with the micelles as a single band. Those neutral species that exist in a partition equilibrium between the buffer solution and the micelles elute between the completely hydrophilic and completely hydrophobic neutrals. Those neutral species favoring the buffer solution elute before those favoring the micelles. Micellar electrokinetic chromatography has been used to separate a wide variety of samples, including mixtures of pharmaceutical compounds, vitamins, and explosives. 

J. A. Marques, K. A. Dill. Solute partitioning into chain molecule interphases monolayers, bilayer membranes and micelles. J Chem Phys 55 434—444, 1986. 

Increased removal of phenanthrene from soil columns spiked with the rhamnolipid mixture synthesized by Pseudomonas aeruginosa UG2 has been demonstrated, and shown to depend both on the increased desorption of the substrate and on partitioning into micelles (Noordman et al. 1998). However, the addition of the biosurfactant from the same strain of Pseudomonas aeruginosa UG2 or of sodium dodecyl sulfate had no effect on the rate of biodegradation of anthracene and phenanthrene from a chronically contaminated soil. 

Highly insoluble molecules are in part transported in the GIT by partitioning into the mixed micelles injected into the lumen from the biliary duct in the duodenum (Fig. 2.3). Mixed micelles consist of a 4 1 mixture of bile salts and phospholipids (Fig. 7.13). In contrast, at the point of absorption in the BBB, highly insoluble molecules are transported by serum proteins. This distinction is expected to be important in in vitro assay modeling. The use of simulated intestinal fluids is appealing. 

The impact of salt concentration on the formation of micelles has been reported and is in apparent accord with the interfacial tension model discussed in Sect. 4.1, where the CMC is lowered by the addition of simple electrolytes [ 19,65, 280,282]. The existence of a micellar phase in solution is important not only insofar as it describes the behavior of amphipathic organic chemicals in solution, but the existence of a nonpolar pseudophase can enhance the solubility of other hydrophobic chemicals in solution as they partition into the hydrophobic interior of the micelle. A general expression for the solubility enhancement of a solute by surfactants has been given by Kile and Chiou [253] in terms of the concentrations of monomers and micelles and the corresponding solute partition coefficients, giving... 

In order to more closely represent the volatilization environment that would be encountered in an evaporation pond, Triton X-100, a non-ionic emulsifier similar to those used in some pesticide formulations, was added to prepared pesticide solutions at 1000 ppm. The presence of this emulsifier caused a decrease in the percent pesticide volatilized in one day in all cases except for mevinphos (Table VI). Three mechanisms are probably in operation here. First, Triton X-100 micelles will exist in solution because its concentration of 1000 ppm is well above its critical micelle concentration of 194 ppm (30). Pesticide may partition into these micelles, reducing the free concentration in water available for volatilization, which will in turn reduce the Henry s law constant for the chemical (31). Second, the pesticides may exhibit an affinity for the thin film of Triton that exists on the water surface. One can no longer assume that equilibrium exists across the air-water interface, and a Triton X-100 surface film resistance... 

Partitioning into oil droplets can be analyzed similarly as partitioning into micelles. Mrestani et al. (102) used microemulsions prepared from non-... 

Fig. 17. Fluorous patches direct the pairing of protein segments in lipid micelles. The hydrophobic peptides partition into lipid micelles, forming a-helices. Then, the superhydrophobic hexafluoroleucine residues seek each other, causing self-association into dimers and higher order aggregates. Fluorine is light, while the backbone of the a-helices is dark. From Ref. [81], with permission.

In MLC, the mobile phase consists of surfactants at concentrations above their critical micelle concentration (CMC) in an aqueous solvent with an alkyl-bonded phase (52). Retention behavior in MLC is controlled by solute partitioning from the bulk solvent into micelles and into stationary phase as well as on direct transfer from the micelles in the mobile phase into the stationary phase. Eluent strength in MLC is inversely related to micelle concentration. A linear relationship exists between the inverse of retention factor and micelle concentration. Similar to what is observed in RPLC, a linear relationship exists between retention in MLC and , the volume fraction of the organic modifier. Modeling retention in MLC is much more complicated than in RPLC. The number of parameters is important. Micelles are obviously a new domain in both liquid chromatography and electrophoresis. Readers interested in the topic will appreciate Ref. 53, a special volume on it. 

Many reduce bioavailability at low doses for drugs with solubility-limited absorption (drug partitioning into micelle, resulting in lower concentration of the free drug)... 

The objective of this portion of the research was to experimentally evaluate surfactant effects on the liquid-liquid separation of hydrophobic oils from a surfactant system. For pump-and-treat subsurface remediation in the absence of surfactant, contaminated ground water would be pumped from the subsurface and through a liquid-liquid extraction column where the contaminant partitions from the aqueous phase into an extraction solvent phase. In the absence of surfactant, the driving force for partitioning is a function of the contaminant hydrophobicity. In the presence of surfactants, the contaminant is subject to competitive partitioning (i.e., into the micelles and into the extracting oil). 

Figure 21.8 Structural models for lamellar PEP-fr-PEO-b-PHMA block copolymer-aluminosilicate composite morphologies with a small PEP block. In the absence of the PEP block, the PEO (black) and PHMA (light grey) chains stretch into their respective domains while the aluminosilicate particles (white) partition into the hydrophilic PEO domain (a). Possible domain structures discussed in the text are illustrated as follows In the balls-in-lamellae structure the small PEP block (dark grey) forms round micellar domains (b). Dimple structure with PEP micelles at the PHMA/PEO-aluminosilicate interface (c). In the pillared-lamellae structure the PEP domains form pillars spanning across the PEO-aluminosilicate domain (d).37 (Reprinted with permission fiomG.E. S.Toombesetal., Chem. Mater. 2008,20,3278-3287. Copyright 2008 American Chemical Society.)...

It is commonly assumed that transfer processes can be modeled by bulk phase thermodynamics and that surface or interfacial effects are negligible. These assumptions may, in the case of partitioning into amphiphilic structures formed by micelles or bilayer membranes, not always be appropriate. These interfacial solvents have a large surface to volume ratio, similar to interfacial solvents used in reversed-phase liquid chromatography. The partitioning into such phases is the basis of the chromatographic separation. 

The ability of micelles or related aggregates to alter reaction rates and selectivity has been an area of active research for the past several decades. Reactants are partitioned into the aggregates by coulombic and hydrophobic interactions the observed rate accelerations are largely a result of the increased localization of the reactants and also of the typical physicochemical properties of the micellar environment, which are significantly different from those of the bulk solvents. This unique ability of the aggregate systems has therefore prompted several scientists to employ micellar media for catalytically carrying out specific reactions. 

Owing to the uncertainties associated with substrate or reagent partitioning into various sub-sites of micelles, the quantitative predictions about the course of reactions and observed changes in the rates of such reactions often become difficult. Consequently attention has been directed toward the design and synthesis of amphiphiles in which either substrate or reagent functions are covalently attached. 

MECC Partitioning into detergent micelles, charge Terabe et al.5... 

Unlike in conventional emulsion polymerization, no monomer droplets exist in a microemulsion polymerization system, and hence, oil-soluble initiators partition into the monomer-swollen micelles, the resultant polymer particles and the water phase. Therefore, in microemulsion polymerization, the polymerization only proceeds in the monomer-swollen micelles and the resultant polymer particles over the entire course of polymerization. Pairs of radicals produced in volumes as small as monomer-swollen micelles and polymer particles may terminate as soon as they are generated. If so, it is expected that the radicals responsible for the polymerization in the monomer-swollen micelles and the resultant polymer particles would usually be those generated from the fraction of the initiator dissolved in the water phase. In order to examine whether this expectation is correct, oil-in-water (O/W) microemulsion polymerizations of St were carried out using four kinds of oil-soluble azo-type initiators with widely different water-solubilities [209]. It was found that the rates of polymerization with these oil-soluble initiators were almost the same irrespective of their water-solubilities, when the polymerizations were carried out with the same rate of radical production for the whole system for all of the oil-soluble initiators used. Moreoever, the rate of polymerization with any of these oil-soluble initiators was only about 1/3 of that with KPS at the same rate of radical production. Considering that the rate of polymerization was pro-... 

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