Critical micelle concentration forming micelles

An aggregate of surfactant molecules or ions in solution. Such aggregates form spontaneously at sufficiently high surfactant concentration, above the critical micelle concentration. The micelles typically contain tens to hundreds of molecules and are of colloidal dimensions. If more than one kind of surfactant forms the micelles, they are referred to as mixed micelles . If a micelle becomes larger than usual as a result of either the incorporation of solubilized molecules or the formation of a mixed micelle, then the term swollen micelle is applied. See also Inverse Micelle. 

Aside from their ability to adsorb at interfaces, the most important aspect of surfactants is their ability to form colloidal-sized aggregates in solution. In dilute solution, the surfactant is present as individual molecules. Increasing the concentration promotes the formation of surfactant aggregates or micelles as shown in Fig. 36.17. The concentration at which micelles start to form is referred to as the critical micelle concentration (CMC). Micelle formation is an important... 

Micelle An aggregate of surfactant molecules in solution. Such aggregates form spontaneously at sufficiently high surfactant concentration, the critical micelle concentration. The micelles are of colloidal dimensions. 

When sodium stearate is placed in water, the hydrophilic carboxylate group encourages the formation of a solution the lipophilic alkyl chain discourages it. The compromise achieved is to form a colloidal dispersion of aggregates called micelles (Figure 18.5). Micelles form spontaneously when the carboxylate concentration exceeds a certain minimum value called the critical micelle concentration. Each micelle is composed of 50-100 individual molecules, with the polar carboxylate groups directed toward its outside where they experience attractive forces with water and sodium ions. The nonpolar hydrocarbon chains are directed toward the interior of the micelle, where individually... 

The system initially consists of water, a practically water-insoluble monomer, an emulsifier, and a water-soluble initiator (see Figure 20-11). The emulsifier forms a great number of micelles above the critical micelle concentration. The micelles solubilize monomer, which causes them to swell. Another fraction of the monomer forms monomer droplets of about 1000-nm diameter. The initiator dissociates into free radicals, which can in some circumstances react with monomers really dissolved in water. A polymerization in the micelle is much more favorable, since a much greater monomer concentration is available there. If such a free radical encounters a monomer loaded emulsifier micelle, the polymerization proceeds in this micelle. The free radical can easily penetrate the micelle because of the loose micellar structure. According to another theory due to Medvedev, a soap micelle free radical is formed by transfer in the aqueous emulsion by an initator free radical, and the transfer free radical then starts the polymerization in the micelle. 

Compounds like sodium stearate, called surfactants in general, can form structures known as micelles in water, once the solution concentration reaches the value known as the critical micelle concentration (cmc). Micelles contain dozens to hundreds of molecules. The cmc depends on the substance, the solvent, and the temperature. 

When poloxamers are introduced into water at a low concentration, the soluble species are only isolated hydrated molecules. When the concentration of a copolymer is increased at constant temperature above the critical micelle concentration (CMC), micelles composed of several molecules are formed. In aqueous medium, such micelles are endowed with a core-shell structure composed of a hydrophobic core and a hydrophilic shell. The equilibrium is illustrated in Figure 4.2. 

Soaps only form true solutions in water at a high dilution. Concentrated solutions of soaps, after exceeding the so-called critical micellar concentration, form micelles, which are agglomerations of many molecules where the polar groups are directed to the surface and the hydrocarbon chains into the interior of micelles. Solutions of alkali soaps hydrolyse in water and thus produce an alkaline solution. Salts of divalent cations, mainly of calcium and magnesium, are practically insoluble in water and in organic solvents they only dissolve with difficulty. These salts are mixtures of varying compositions and with different ratios of cations and acyls. Soaps of fatty acids and other acidic components, such as phosphoric acid derivatives, can also occur in foods. 

Emulsion polymerization of vinyl chloride is initiated by a water-soluble initiator such as potassium persulfate. Initially in the reactor, monomer droplets are dispersed in the aqueous phase (continuous phase) containing initiator and surfactant (emulsifier). As the reactor content is heated, the initiator decomposes into free radicals. When the surfactant concentration exceeds the critical micelle concentration (CMC), micelles are formed. Free radicals or oligomers formed in the aqueous phase are then captured by these micelles. Vinyl chloride monomer is slightly soluble in water. As the monomer dissolved in water diffuses into micelles containing radicals, polymerization occurs. With an increase in monomer conversion in the polymer particles, separate monomer droplets become smaller and eventually they disappear. The monomer concentration in polymer particles is constant as long as liquid monomer droplets exist. The rate of emulsion polymerization is represented by... 

Critical micelle concentration (Section 19 5) Concentration above which substances such as salts of fatty acids aggre gate to form micelles in aqueous solution Crown ether (Section 16 4) A cyclic polyether that via lon-dipole attractive forces forms stable complexes with metal 10ns Such complexes along with their accompany mg anion are soluble in nonpolar solvents C terminus (Section 27 7) The amino acid at the end of a pep tide or protein chain that has its carboxyl group intact—that IS in which the carboxyl group is not part of a peptide bond Cumulated diene (Section 10 5) Diene of the type C=C=C in which a single carbon atom participates in double bonds with two others... 

Emulsification is the process by which a hydrophobic monomer, such as styrene, is dispersed into micelles and monomer droplets. A measure of a surfactant s abiUty to solubilize a monomer is its critical micelle concentration (CMC). Below the CMC the surfactant is dissolved ia the aqueous phase and does not serve to solubilize monomer. At and above the CMC the surfactant forms spherical micelles, usually 50 to 200 soap molecules per micelle. Many... 

Critical micelle concentration (Section 19.5) Concentration above which substances such as salts of fatty acids aggregate to form micelles in aqueous solution. 

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]. 

In the latter function, the reagent behaves as a surfactant and forms a cationic micelle at a concentration above the critical micelle concentration (1 x 10 4M for CTMB). The complexation reactions occurring on the surface of the micelles differ from those in simple aqueous solution and result in the formation of a complex of higher ligand to metal ratio than in the simple aqueous system this effect is usually accompanied by a substantial increase in molar absorptivity of the metal complex. 

Surfactants have a unique long-chain molecular structure composed of a hydrophilic head and hydrophobic tail. Based on the nature of the hydrophilic part surfactants are generally categorized as anionic, non-ionic, cationic, and zwitter-ionic. They all have a natural tendency to adsorb at surfaces and interfaces when added in low concentration in water. Surfactant absorption/desorption at the vapor-liquid interface alters the surface tension, which decreases continually with increasing concentrations until the critical micelle concentration (CMC), at which micelles (colloid-sized clusters or aggregates of monomers) start to form is reached (Manglik et al. 2001 Hetsroni et al. 2003c). 

As an even more explicit example of this effect Figure 6 shows that EPM is able to reproduce fairly well the experimentally observed dependence of the particle number on surfactant concentration for a different monomer, namely methyl methacrylate (MMA). The polymerization was carried at 80°C at a fixed concentration of ammonium persulfate initiator (0.00635 mol dm 3). Because methyl methacrylate is much more water soluble than styrene, the drop off in particle number is not as steep around the critical micelle concentration (22.) In this instance the experimental data do show a leveling off of the particle number at high and low surfactant concentrations as expected from the theory of particle formation by coagulative nucleation of precursor particles formed by homogeneous nucleation, which has been incorporated into EPM. 

Micelles the mostly spherical nanoscale aggregates formed by amphiphilic compounds above their critical micelle concentration in aqueous solution have a narrow size distribution and are dynamic, because there is a fast exchange of amphiphiles in solution and those incorporated in micelles. However, micelles are defined as self-assembled structures, since the structure is in thermodynamical equilibrium. 

Surfactants greatly improve the performance of trans-cinnamaldehyde as a corrosion inhibitor for steel in HCl [741,1590,1591]. They act by enhancing the adsorption at the surface. Increased solubility or dispersibility of the inhibitor is an incidental effect. N-dodecylpyridinium bromide is effective in this aspect far below its critical micelle concentration, probably as a result of electrostatic adsorption of the monomeric form of N-dodecylpyridinium bromide. This leads to the formation of a hydrophobic monolayer, which attracts the inhibitor. On the other hand, an ethoxylated nonylphenol, a nonionic surfactant, acts by incorporating the inhibitor into micelles, which themselves adsorb on the steel surface and facilitate the adsorption of trans-cinnamaldehyde. 

Aqueous micellar solutions, i.e. solutions containing a surfactant at a concentration above its critical micelle concentration, have been studied extensively during the last decade, in part from curiosity, and because of the possibility of providing unique chromatographic selectivity compared to conventional RPC [345-349]. Above the critical micelle concentration individual surfactant molecules self-aggregate to form structures known as micelles which are microscopically... 

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