Critical monomer concentration CMC

Amphiphilic molecules such as lipids have an extremely low solubility in water and tend to self-associate and form lyotropic liquid crystals [1] if their monomer concentration in aqueous surroundings exceeds a critical value (the critical monomer concentration, (CMC), [2]). This self-organization is due to the hydrophobic effect [2], It leads to the formation of micro- and mesoscopic structures, among them micellar, hexagonal, lamellar and cubic phases [3] and the respective transitions between them. ... 

During Stage I the number of polymer particles range from 10 to 10 per mL. As the particles grow they adsorb more emulsifier and eventually reduce the soap concentration below its critical micelle concentration (CMC). Once below the CMC, the micelles disappear and emulsifier is distributed between the growing polymer particles, monomer droplets, and aqueous phase. 

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... 

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]. 

Very large solvent effects arc also observed for systems where the monomers can aggregate either with themselves or another species. For example, the apparent kp for polymerizable surfactants, such as certain vinyl pyridinium salts and alkyl salts of dimethylaminoalkyl methacrylates, in aqueous solution above the critical micelle concentration (cmc) are dramatically higher than they are below the cmc in water or in non-aqueous media.77 This docs not mean that the value for the kp is higher. The heterogeneity of the medium needs to be considered. In the micellar system, the effective concentration of double bonds in the vicinity of the... 

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). 

Monomer/Micelle Equilibrium Mixtures of surfactants, like any surfactant species in an aqueous solution, give rise to monomer or micelle aggregates provided that the concentration reaches a minimum value, called the critical micellar concentration (CMC). The micelles thus formed are mixed, i.e. made up of the different surfactant species in solution. 

The concentration of micellized surfactant is that of total surfactant less that of monomer which is assumed to be given by the critical micelle concentration (cmc). The overall first-order rate constant kv is then given by (1). 

Figure 10.11 As the aggregate number n increases, so the fraction of the added surfactant that goes into the micelle (as y ) varies more steeply with total concentration of surfactant monomer (as V). The critical micelle concentration (CMC) is the midpoint of the region over which the concentration of the micelle changes (Reproduced by permission of Wiley Interscience, from The Colloidal Domain by D. Fennell Evans and Hakan Wennerstrom)...

We call the centre of the concentration range the critical micelle concentration (CMC). As an over-simplification, we say the solution has no colloidal micelles below the CMC, but effectively all the monomer exists as micelles above the CMC. As no micelles exist below the CMC, a solution of monomer is clear - like the solution of dilute soap in the bath. But above the CMC, micelles form in solution and impart a turbid aspect owing to Tyndall light scattering. This latter situation corresponds to washing the face in a sink. 

The surface active agents (surfactants) may be cationic, anionic or non-ionic. Surfactants commonly used are cetyltrimethyl ammonium bromide (CTABr), sodium lauryl sulphate (NaLS) and triton-X, etc. The surfactants help to lower the surface tension at the monomer-water interface and also facilitate emulsification of the monomer in water. Because of their low solubility surfactants get fully dissolved or molecularly dispersed only at low concentrations and at higher concentrations micelles are formed. The highest concentration where in all the molecules are in dispersed state is known as critical micelle concentration (CMC). The CMC values of some surfactants are listed in table below. 

Micelles tend to aggregate, and there are many ways to measure their concentration, including surface tension measurements. The midpoint of the concentration range over which micellar aggregation occurs is called the critical micellar concentration (CMC). Below the CMC, added bile-salt molecules dissolve in the form of monomers above the CMC, added bile-salt molecules form micelles, leaving the monomeric concentration essentially constant. The pH at which CMC formation occurs is called the critical micellar pH, (CMpH). Table 1.1 lists values for some of the bile acids mentioned in this review. 

Ideal Mixed Micelles. The Critical Micelle Concentration (CMC) is the lowest surfactant concentration at which micelles form the lower the CMC, the greater the tendency of a system to form micelles. When the total surfactant concentration equals the CMC, an infintesimal fraction of surfactant is present as micelles therefore, the CMC is equal to the total monomer concentration in equilibrium with the micellar pseudo—phase. The CMC for monomer—micelle equilibrium is analogous to the dew point in vapor—liquid equilibrium. 

Aqueous micelles 3D 20-40 A diameter Dissolution of surfactant in water at concentrations above the critical micelle concentration (CMC) Dynamic equilibrium between monomers and micelles Particle formation was only possible at the micellar surface or close to it 55, 101... 

The initial concentration, C0, in square centimeters, was determined directly from the area under the curve of a synthetic boundary trace. Although usual practice is to place solvent in one cell and the solution in the other, the solvent used in this work was a solution of bile salt slightly above its critical micellar concentration, CMC (15), usually 0.5 gram per 100 ml. The solution, which was placed in the other cell, was a more concentrated solution (1.5 to 5.0 grams per 100 ml.). Therefore, since both the solvent and the solution were saturated with monomers, C0 represents an initial concentration difference of bile salts in the micellar phase. The pertinent data for each equilibrium ultracentrifugation experiment are presented in Table I. 

An emulsifier is a molecule that possesses both polar and nonpolar moieties, i.e., it is amphiphilic. In very dilute water solutions, emulsifiers dissolve and exist as monomers, but when their concentration exceeds a certain minimum, the so-called critical micelle concentration (CMC), they associate spontaneously to form aggregates - micelles. Micelles are responsible for many of the processes such as enhancement of the solubility of organic compounds in water, catalysis of many reactions, alteration of reaction pathways, rates and equilibria, reaction loci for the production of polymers, etc. 

A temperature-composition phase diagram for a surfactant solution is a characteristic phase diagrarr that delineates the conditions under which crystalline surfactant, monomers, or micelles will exist. On the phase diagram shown in Figure 12.5 (Smirnova, 1995), L represents the liquid phase, S the solid phase, and )(the surfactant mole fraction. The critical micellar temperature, CMT, is deLned as the line between the crystalline and micellar phases. Micelle formation occurs at temperatures greater than the CMT. The critical micellar concentration, CMC, line separates the micellar and... 

Monomer Solutions. At surfactant concentrations less than the critical micelle concentration (cmc), all the surfactant is in monomeric form and the equilibrium between the protonated and neutral species of an alkyldimethyl amine oxide can be described by a classical dissociation constant, Ka ... 

The CMC in the curve represents the critical micelle concentration (CMC) at which the surfactant molecules start forming aggregates known as micelles. Below CMC, surfactant molecules are in monomeric form and the surface or interfacial tension reduces dramatically with the increase of surfactant concentration in the bulk. The slope of the curve below the CMC is constant and reaches its maximum value since the surface or interface is saturated with surfactant monomers [2, 16]. For the dilute solution of non-ionic surfactant ... 

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