Dependence upon surfactant concentration

Equation (8) constitutes the basic thermodynamic equation for the calculation of the radius of the globules. Of course, explicit expressions, in terms of the radius of the globules and volume fraction, are needed fort, C and af before such a calculation can be carried out. Expressions for Af will be provided in another section of the paper, but it is difficult to derive expressions fory and C. One may, however, note that y (and also C) depends on the radius for the following two reasons (1) its value depends upon the concentrations of surfactant and cosurfactant in the bulk phases, which, because the system is closed, depend upon the amounts adsorbed on the area of the internal interface of the microemulsion (2) in addition to the above mass balance effect, there is a curvature effect on y (this point is examined later in the paper). 

More drastic changes in the CMC and N are observed when additives are present in the micelle-forming surfactant - water systems. The addition of ionic species (i.e. electrolytes) usually results in an increase in the aggregation number and a reduction in the CMC. Table III (and Table II) present some data which illustrate this effect. Depending upon the concentration, the presence of water miscible organic molecules can either enhance or inhibit micelle formation. 

Effect of initiator level. The effect of increasing amounts of cobalt(III) acetylacetonate upon the rate of polymerisation is complex. Whilst the rate always appears to increase as the initiator level increases (in contrast to the behaviour observed when the surfactant level is increased), the order of reaction with respect to initiator depends upon the concentration of surfactant in the aqueous phase. The results summarised in Figure 9 show that the order is approximately the Smlth-Ewart value of 0.4 at high surfactant concentrations, whereas it falls markedly as the surfactant level in the reaction system is lowered. Figure 10 illustrates the rather surprising observation that the order of reaction with respect to initiator appears to vary linearly with the logarithm of the surfactant concentration. 

Denoyel and coworkers [61] used a thermodynamic adsorption method to study the adsorption of nonionic and anionic surfactants onto silica, kaolin, and alumina particles. The surfactants formed various structures depending upon their concentrations in the solution. It was found that 2D hemimicelles with low coverage were formed at very low surfactant concentrations. With... 

Microstructure of Film Formed from Micellar Solution. The dependence of foam stability upon surfactant concentration is well known. Specifically, above a certain surfactant concentration (after cmc), the stability of a foam increases sharply with surfactant concentration. This fact is used in industry, where stable foams are created with surfactant concentrations far above the cmc. 

There appear then three primary mechanisms for stabilizing (or destabilizing) a three phase foam. The first derives from the micelle structuring in the film and depends directly upon surfactant concentration and electrolyte concentration. The second is a surface tension gradient (Marangoni) mechanism which relates to the short range intermolecular interactions and the rate of surface expansion. And the third is an oil droplet size effect which depends upon the magnitude of the dynamic interfacial tension. 

The addition level is predicated on the degree of crosslinking required and is dependent upon the concentration of the carboxyl functionality of the resin (polymer) used. The optimum ZINPLEX 15 level must be determined experimentally to assure maximum performance properties and stability of the end coating. With certain polymer systems, prestabilization may be necessary prior to the addition of ZINPLEX 15. Surfactants such as the high ethylene oxide nonionics (i.e. TRITON X405) offer good stabilizing properties. 

Oils. SANS has been used to establish the effect of the addition of a hydrophobic guest (dodecane) on the behavior of liquid crystalline phases, in particular the lamellar and columnar phases of mixtures of the non-ionic surfactant C16E7 with D2O, as well as to determine the distribution of the hydrophobic guest in the microstructure. SANS showed that the presence of the hydrophobic guest molecule, in some cases, stabilized a particular phase structure, (for example lamellar phases formed at lower temperatures in the presence of dodecane) while in other cases it destabilized it, eventually (depending upon the concentration of dodecane added) causing the phase to disappear. In the lamellar phase, dodecane was found to be totally segregated in the center of the bilayer. 

DBS) are employed. The rate of electron transfer and its dependence upon chromophore concentration suggest that the electron tunnels from a chromophore on the inner surface of the vesicle to one on the outer surface rather than being carried by flipping of the surfactant chromophore from one surface to the other. In the system involving amphiphilic zinc porphyrin... 

Some examples of micellar rate enhancements of bimolecular reactions of electrophiles are shown in Table 5. Generally the surfactant was SDS with added electrophile, e.g. H30+ or a metal ion, but sulfonic acids were also used so that HaO+ was the counterion and there was no interionic competition. The maximum rate enhancements, knl, depend upon the specific conditions of the experiment, and, as predicted by the pseudophase ion-exchange model, generally decrease with increasing concentration of the electrophilic ion. In some cases the reactions were too fast for measurement... 

The question then becomes that of the significance of the ion-exchange and mass-law equations which successfully account for the dependence of micellar rate constants upon the concentrations of surfactant and reactive and inert counterions. It seems reasonable to continue to use these descriptions at the present time, despite uncertainties as to the location of hydrophilic counterions at the micellar surface. 

An impressive body of evidence supports these generalizations. This evidence has been reviewed (Romsted, 1984) and it does not seem necessary to discuss it in detail here, but some examples will be given and some exceptions to these generalizations will be mentioned. Some reactions of OH- are shown in Table 3 for both inert and reactive ion surfactants, and Table 4 gives data for reactions of other hydrophilic ions. Reactions of hydrophobic nucleophiles are shown in Table 2. For all these reactions second-order rate constants in the micellar pseudophase are compared with those in water. For some reactions we also give values of krcl, i.e. the rate constant relative to that in water. These values depend upon the reactant concentration and are included merely to provide an indication of the micellar rate effects. Other examples of micellar rate effects are given in the Appendix. 

In a recent paper, the interaction of various simple flavonoids with an anionic surfactant, sodium dodecyl sulfate (SDS) in aqueous solution, has been studied through absorption spectroscopy as a function of the concentration of the surfactant above and below the critical micelle concentration.The approximate number of additive molecules (flavonoids) incorporated per micelle was estimated at a particular concentration of SDS. Incorporation of flavonoids in micelles shifted the UV absorption bands toward higher wavelengths, and the bathochromic shifts also depended upon the nature of the surfactant head group. 

It has been shown,therefore, that the behavior of molecular assemblies can be divided into three regions depending upon the amount of MEGA-n surfactant (1) at higher MEGA-n concentration where dlalkyl amphiphile is... 

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