Micelles mechanism

We have recently observed in our laboratory that water washes of undamaged leaves in a number of plants contained sterols and other lipids in sufficiently high concentration comparable with concentrations used in typical laboratory bioassays. These aqueous lipid solutions are frequently accompanied by long-chain (C-12 to C-18) fatty acids. We therefore suggest that micelle formation between the lipids and fatty acids may occur. By this mechanism the lipid solubility in the aqueous medium is significantly enhanced, thus allowing the release of otherwise water-insoluble plant constituents into the environment. Presently, experiments are in progress in our laboratory to provide further evidence for the "micelle-mechanism" of allelopathlc lipids. 

Figures 5 and 6 show that the concentration of the two surfactants in the effluents increases simultaneously with the production of the desorbent, which confirms the mixed micellization mechanism described above. Figure 5, where the three additives are produced lately, illustrates the phenomenon particularly well. At the lower pH corresponding to strong adsorption conditions for sulfonate (test 4), the one pore-volume micellar slug would have been entirely consumed by the medium in the absence of any desorbent.

With P,P -di(2-ethylhexyl) butanediphosphonic acid (H2DEH[BuDP]), U(VI) data analysis points to the formation of two separate extracted complexes with different stoichiometries whose mechanisms are not consistent with extraction via a micelle mechanism." ... 

Bringe, N. A., and Kinsella, J. E. (1990). Acidic coagulation of casein micelles Mechanisms inferred from spectrophotometric studies. J. Dairy Res. SI, 365-375. 

This coated micelle mechanism remained a central concept in the mechanism of mesoporous material formation for several years. It was used by Yang et to explain the formation of spectacular rope-like,... 

According to the initiation-in-the-adsorbed-emulsifier-layer mechanism, the particle nucleation occurs in the adsorbed monomer layer whether it is in the micelles, polymer particles or emulsion droplets. Conceptually, this mechanism is similar to the initiation-in-micelles mechanism (although the equations are somewhat different). A radical which is generated in the aqueous phase and diffuses to an adsorbed emulsifier layer is likely to initiate polymerization... 

Figure 3 shows a typical variation of the number of particles N with emulsifier concentration (20-22). At low emulsifier concentrations, well below the cmc, the value of N increases, slowly at first and then more rapidly, until it rises almost vertically at the cmc, to level off at emulsifier concentrations well above the cmc. This shape is consistent with the initiation-in-micelles mechanism, especially in view of the results shown in Figure 2. 

The initiation-in-micelles mechanism (4) postulated that the monomer droplets serve as reservoirs, feeding monomer to the polymerizing monomer-swollen micelles and -polymer particles by diffusion through the aqueous phase. The failure of the 1-lOym diameter monomer droplets to capture radicals was attributed to their negligible surface area relative to that of the monomer droplets. Indeed, hypothetical calculations of the relative surface areas of monomer-swollen micelles and monomer droplets show that it is unlikely that radicals diffusing to the monomer-water interface would enter monomer droplets and initiate polymerization. This conclusion was supported for isoprene emulsion polymerization by the low concentration of monomer found in monomer droplets separated by centrifugation and the retention of a spherical form by monomer drops in a polymerizing medium (4). 

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... 

FT-EPR spectra of the ZnTPPS/DQ system in a solution of cetyltriinethylaininonium chloride (CTAC), a cationic surfactant, are shown in figme BE 16.21. As in the TX100 solution, both donor and acceptor are associated with the micelles in the CTAC solution. The spectra of DQ at delays after the laser flash of less than 5 ps clearly show polarization from the SCRP mechanism. While SCRPs were too short-lived to be observed in TXlOO solution, they clearly have a long lifetime in this case. Van Willigen and co-workers... 

Reversibly fonned micelles have long been of interest as models for enzymes, since tliey provide an amphipatliic environment attractive to many substrates. Substrate binding (non-covalent), saturation kinetics and competitive inliibition are kinetic factors common to botli enzyme reaction mechanism analysis and micellar binding kinetics. 

Chain-Growth Associative Thickeners. Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain-growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles (50). Although the initiation and propagation occurs primarily in the aqueous phase, when the propagating radical enters the micelle the hydrophobically modified monomers then polymerize in blocks. In addition, the hydrophobically modified monomer possesses a different reactivity ratio (42) than the unmodified monomer, and the composition of the polymer chain therefore varies considerably with conversion (57). The most extensively studied monomer of this class has been acrylamide, but there have been others such as the modification of PVAlc. Pyridine (58) was one of the first chain-growth polymers to be hydrophobically modified. This modification is a post-polymerization alkylation reaction and produces a random distribution of hydrophobic units. 

An expression for the number of particles formed during Stage I was developed, assuming micellar entry as the formation mechanism (13), where k is a constant varying from 0.37 to 0.53 depending on the relative rates of radical adsorption in micelles and polymer particles, r is the rate of radical generation, m is the rate of particle growth, is the surface area covered by one surfactant molecule, and S is the total concentration of soap molecules. 

Fig. 4. MiceUular gelation mechanism. A shows micelle nuclei, highly cross-linked B, boundary where micelle growth terminates in styrene block polymers.

Anionic Surfactants. PVP also interacts with anionic detergents, another class of large anions (108). This interaction has generated considerable interest because addition of PVP results in the formation of micelles at lower concentration than the critical micelle concentration (CMC) of the free surfactant the mechanism is described as a "necklace" of hemimicelles along the polymer chain, the hemimicelles being surrounded to some extent with PVP (109). The effective lowering of the CMC increases the surfactant s apparent activity at interfaces. PVP will increase foaming of anionic surfactants for this reason. 

In some cases, dye-forming moieties attached to a polymeric backbone, called a polymeric coupler, can replace the monomeric coupler in coupler solvent (51). In other reports, very small particles of coupler solubilized by surfactant micelles can be formed through a catastrophic precipitation process (58). Both approaches can eliminate the need for mechanical manipulation of the coupler phase. 

Destruction of the casein micelles in the milk with subsequent precipitation of the casein can be accomplished in a number of ways. The action of heat or the action of alcohols, acids, salts and the enzyme rennet all bring about precipitation. In commercial practise the two techniques used employ either acid coagulation or rennet coagulation mechanisms. 

The reasons for self-assembly and the mechanisms necessary conditions for the aggregation into micelles, mono- or bilayers, structure of aggregates, distribution of aggregation numbers, etc. 

A macroporous polystyrene-divinylbenzene copolymer is produced by a suspension polymerization of a mixture of monomers in the presence of water as a precipitant. This is substantially immiscible with the monomer mixture but is solubilized with a monomer mixture by micelle-forming mechanisms in the presence of the surfactant sodium bis(2-ethylhexylsulfosuccinate) (22). The porosity of percentage void volume of macroporous resin particles is related to percentage weight of the composite (50% precipitant, 50% solvent) in the monomer mixture. 

The kinetic mechanism of emulsion polymerization was developed by Smith and Ewart [10]. The quantitative treatment of this mechanism was made by using Har-kin s Micellar Theory [18,19]. By means of quantitative treatment, the researchers obtained an expression in which the particle number was expressed as a function of emulsifier concentration, initiation, and polymerization rates. This expression was derived for the systems including the monomers with low water solubility and partly solubilized within the micelles formed by emulsifiers having low critical micelle concentration (CMC) values [10]. 

Therefore, the polymerization progresses within the micelle structure by following the traditional mechanism of emulsion polymerization. 

GPC distributions 553 mechanisms 551 4 precursors 549, 551 microgcl formation 554-5 seif-condensing v iuyl polymerization 555-6 shell-erossjinking of micelles 555 dendritic cores 556-7 thiocarbonvltbio RAFT agents 464, 501-2, 505-14... 

Mechanisms of micellar reactions have been studied by a kinetic study of the state of the proton at the surface of dodecyl sulfate micelles [191]. Surface diffusion constants of Ni(II) on a sodium dodecyl sulfate micelle were studied by electron spin resonance (ESR). The lateral diffusion constant of Ni(II) was found to be three orders of magnitude less than that in ordinary aqueous solutions [192]. Migration and self-diffusion coefficients of divalent counterions in micellar solutions containing monovalent counterions were studied for solutions of Be2+ in lithium dodecyl sulfate and for solutions of Ca2+ in sodium dodecyl sulfate [193]. The structural disposition of the porphyrin complex and the conformation of the surfactant molecules inside the micellar cavity was studied by NMR on aqueous sodium dodecyl sulfate micelles [194]. 

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