Mechanism of micellization

Salkar, R.A. Mukesh, D. Samant, S.D. Manohar, C. Mechanism of micelle to vesicle transition in cationic-anionic surfactant mixtures. Langmuir 1998, 14, 3778-3782. 

The schematic shows that the transport of monomers and micelles as well as the mechanism of micelle kinetics have to be taken into account in a reasonable physical model. 

The kinetics and mechanisms of micelle-catalysed reactions have been intensively studied in recent years and they are much too complicated to be discussed here in detail (80,81). Micelles may also be considered as phase transfer agents of a sort which take the organic phase reagent into the aqueous phase for r eaction. 

Density simirlation for four Japanese coals. Eneigy Fuels 7 469-472 Mrrrgich J, Rodriguez M, Aray Y (1996) Molecrrlar recognition and molecular mechanics of micelles of some model asphaltenes and resins. Energy Fuels 10 68-76 Nakamirra K, Mirrata S, Nomura M (1993) CAMD study of coal model molecules. 1. Estimation of physical density of coal model molecules. Energy Fuels 7 347-350 Olah GA, Molnar A (1995) Hydrocarbon Chemistry, John Wiley Sons, Inc. 

If the interfacial area is small, it can only accommodate a small number of molecules. When, as usual, many more surfactant molecules than this are present, the majority cannot escape from the bulk liquid to the interface and the affinities of the hydrophilic and lipophilic groups must be satisfied by other means if thermodynamic stability is to be achieved. This again occurs by a process of orientation. In an aqueous medium the hydrophobic groups turn towards and associate with one another, forming in effect their own oil phase, surrounded by the hydrophilic groups turned outwards and anchored in the water. This type of internal association and orientation has been termed micelle formation. Micelles are usually spherical in shape. The escape mechanism of micelle formation only becomes operative above a certain minimum surfactant concentration. This concentration has been termed the critical micelle concentration (CMC). CMCs vary from about 5 x 10 mol 1 for the most hydrophilic to about 5 x 10 mol 1 for the most hydrophobic types of surfactant. They are influenced by electrolytes, especially in the case of ionic surfactants, and also by other polar/non-polar chemical compounds such as alcohols, amides and, of course, other surfactants. 

Murgich, J. Rodriguez, J. M Aray, Y. (1999). Molecular Recognition and Molecular Mechanics of Micelles of Some Model Asphaltenes and Resins. Energy Fuels, 10, 68-76... 

J. Murgich, (1996). Molecular recognition and molecular mechanics of micelles of some... 

Having reviewed the properties of single adsorption monolayers, we proceed with the couples of interacting monolayers the thin liquid films. First, we present the thermodynamics of thin films, and then we describe the molecular theory of the surface forces acting in the thin films. We do not restrict ourselves to the conventional DLVO (Deijaguin, Landau, Verwey, Overbeek) forces [2,3], but consider also the variety of the more recently discovered non-DLVO surface forces [4]. The importance of the micelle-micelle interaction for the mechanism of micelle growth is also discussed. 

The mechanisms of micelle-catalyzed reactions have been studied not only by analogy with the Michaelis-Menten equation for enzymatic reactions but also from the perspective of volume fractions of the two-part reaction system consisting of the micelles and the intermicellar bulk solutions.The kinetics of this reaction has been successfully used only when the micellar concentrations are much higher than the reactant concentrations. However, micellar concentrations near the CMC are often less than the reactant concentrations. In such cases, the distribution of reactants among micelles must be taken into consideration, which is essentially a thermodynamic problem (Chapter 9). Reactant is a better technical term than substrate for micelle-catalyzed reactions. 

Although the mechanism of micelle formation is still incompletely understood, a generally accepted mechanism for such a complex dynamic process is represented by Equation 1.20. The stability of aggregate A (n = 2, 3, 4,. ..) is governed by both polar/ionic and van der Waals attractive as well as repulsive forces. The rate constants, kj - , stand for diffusion-controlled association processes and, hence, the magnitudes of lie within 10 to 10 M sec for all values of n > 2. But the values of k are expected to decrease with... 

Murgich, J., Rodriguez, J., Aray, Y. 1996. Molecular recognition and molecular mechanics of micelles of some model asphaltenes and resins. Energy Fuels 10(l) 68-76. 

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. 

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]. 

An important kinetic aspect of the washing process is the rate of removal of oily stains by surfactant micelles. Several mechanisms have been suggested for the solubilization of oil into micelles. Chan [67] and Carroll [68] propose diffusion of micelles toward the oil-water interface, followed by demicellization,... 

In another study of the physical behavior of soap-LSDA blends, Weil and Linfield [35] showed that the mechanism of action of such mixtures is based on a close association between the two components. In deionized water this association is mixed micellar. Surface tension curves confirm the presence of mixed micelles in deionized water and show a combination of optimum surface active properties, such as low CMC, high surface concentration, and low surface concentration above the CMC. Solubilization of high Krafft point soap by an LSDA and of a difficulty soluble LSDA by soap are related results of this association. Analysis of dispersions of soap-LSDA mixtures in hard water shows that the dispersed particles are mixtures of soap and LSDA in the same proportion as they were originally added. These findings are inconsistent with the view that soap reacts separately with hard water ions and that the resulting lime soap is suspended by surface adsorption of LSDA. The suspended particles are responsible for surface-active properties and detergency and do not permit deposits on washed fabric unlike those found after washing with soap alone. 

The most important nanomaterial synthesis methods include nanolithography techniques, template-directed syntheses, vapor-phase methods, vapor-liquid-solid (VLS) methods, solution-liquid-solid (SLS) approaches, sol-gel processes, micelle, vapor deposition, solvothermal methods, and pyrolysis methods [1, 2]. For many of these procedures, the control of size and shape, the flexibility in the materials that can be synthesized, and the potential for scaling up, are the main limitations. In general, the understanding of the growth mechanism of any as-... 

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. 

For the mechanism of azolide hydrolysis under specific conditions like, for example, in micelles,[24] in the presence of cycloamyloses,[25] or transition metals,[26] see the references noted and the literature cited therein. Thorough investigation of the hydrolysis of azolides is certainly important for studying the reactivity of those compounds in chemical and biochemical systems.[27] On the other hand, from the point of view of synthetic chemistry, interest is centred instead on die potential for chemical transformations e.g., alcoholysis to esters, aminolysis to amides or peptides, acylation of carboxylic acids to anhydrides and of peroxides to peroxycarboxylic acids, as well as certain C-acylations and a variety of other preparative applications. 

LJ Naylor, V Bakatselou, JB Dressman. Comparison of the mechanism of dissolution of hydrocortisone in simple and mixed micelle systems. Pharm Res 10 865-870, 1993. 

Penetration enhancers are low molecular weight compounds that can increase the absorption of poorly absorbed hydrophilic drugs such as peptides and proteins from the nasal, buccal, oral, rectal, and vaginal routes of administration [186], Chelators, bile salts, surfactants, and fatty acids are some examples of penetration enhancers that have been widely tested [186], The precise mechanisms by which these enhancers increase drug penetration are largely unknown. Bile salts, for instance, have been shown to increase the transport of lipophilic cholesterol [187] as well as the pore size of the epithelium [188], indicating enhancement in both transcellular and paracellular transport. Bile salts are known to break down mucus [189], form micelles [190], extract membrane proteins [191], and chelate ions [192], While breakdown of mucus, formation of micelles, and lipid extraction may have contributed predominantly to the bile salt-induced enhancement of transcellular transport, chelation of ions possibly accounts for their effect on the paracellular pathway. In addition to their lack of specificity in enhancing mem-... 

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