Surfactant concentration, maximum

Of all the characteristic points in the phase diagram, the composition of the middle phase is most sensitive to temperature. Point M moves in an arc between the composition of the bottom phase (point B) at and the composition of the top phase (point T) at reaching its maximum surfactant concentration near T = - -T )/2. (Points B and Tmove by much smaller amounts, also.) The complete nonionic-amphiphile—oh—water—temperature... 

There is good correlation between the concentration giving the maximum surface dilatational viscosity and that giving the best foam performance. The nonylphenol 10 EO is a low-foaming nonionic surfactant with a maximum foam height of 150 ml in this test, whereas AOS produced 670 ml of foam. Figure 12 clearly shows that there is an optimum surfactant concentration for a dynamic process such as foam generation. 

For normalization of the value of the heat transfer enhancement, we used its magnitude at the maximum for each curve. The result of such normalization is shown in Fig. 2.59. In this figure, C is the solution concentration, Cq is the characteristic concentration, h is the heat transfer coefficient at given values of the solution concentration and the heat flux q, /zmax is the maximum value of the heat transfer coefficient at the same heat flux, and /zw is the heat transfer coefficient for pure water at the same heat flux q. Data from all the sources discussed reach the same value of 1.0 at the magnitude of relative surfactant concentration equal to 1.0. 

Most studies of micellar systems have been carried out on synthetic surfactants where the polar or ionic head group may be cationic, e.g. an ammonium or pyridinium ion, anionic, e.g. a carboxylate, sulfate or sulfonate ion, non-ionic, e.g. hydroxy-compound, or zwitterionic, e.g. an amine oxide or a carboxylate or sulfonate betaine. Surfactants are often given trivial or trade names, and abbreviations based on either trivial or systematic names are freely used (Fendler and Fendler, 1975). Many commercial surfactants are mixtures so that purity can be a major problem. In addition, some surfactants, e.g. monoalkyl sulfates, decompose slowly in aqueous solution. Some examples of surfactants are given in Table 1, together with values of the critical micelle concentration, cmc. This is the surfactant concentration at the onset of micellization (Mukerjee and Mysels, 1970) and can therefore be taken to be the maximum concentration of monomeric surfactant in a solution (Menger and Portnoy, 1967). Its value is related to the change of free energy on micellization (Fendler and Fendler, 1975 Lindman and Wennerstrom, 1980). 

According to this equation, the plot of l/kw as function of C would show a minimum and the plot beyond Cmin would be linear with a positive slope and positive intercept. However, at the optimum surfactant concentration corresponding to the maximum in the plot of kv against [Surfactant], the following relationship is obtained. 

To what extent the reaction occurring in each of the two separate pseudophases contributes to the overall observed reaction depends on the local reaction rate constants and local concentrations. Typically, plots representing the rate of reaction or the (related) observed second-order rate constant obs,2 as a function of surfactant concentration go through a maximum. This maximum is related to the lowest surfactant concentration where both reactants are fully bound in the micellar pseudophase, that is, local concentrations in the micellar pseudophase are highest. 

A similar result is observed when the maximum height achieved (imax) is plotted as a function of surfactant concentration (Fig. 6). However, the more interesting observation is that for all concentrations above CMC (for which a = 22 dyn/cm), the maximum height predicted for perfect wetting conditions (i.e 6 = 0), is... 

The determination of the enzyme activity as a function of the composition of the reaction medium is very important in order to find the optimal reaction conditions of an enzyme catalysed synthesis. In case of lipases, the hydrolysis of p-nitrophenyl esters in w/o-microemulsions is often used as a model reaction [19, 20]. The auto-hydrolysis of these esters in w/o-microemulsions is negligible. Because of the microstructure of the reaction media itself and the changing solvent properties of the water within the reverse micelles, the absorbance maximum of the p-nitrophenol varies in the microemulsion from that in bulk water, a fact that has to be considered [82]. Because of this, the water- and surfactant concentrations of the applied micro emulsions have to be well adjusted. 

The conditions for synergism in surface tension reduction efficiency, mixed micelle formation, and Surface tension reduction effectiveness in aqueous solution have been derived mathematically together with the properties of the surfactant mixture at the point of maximum synergism. This treatment has been extended to liquid-liquid (aqueous solution/hydrocarbon) systems at low surfactant concentrations.) The effect of chemical structure and molecular environment on the value of B is demonstrated and discussed. 

The cmc at the point of maximum synergism, i.e., the minimum total mixed surfactant concentration in the solution phase required for mixed micelle formation, C 2 nin given by the relationship ... 

Apart from anomalous situations where surfactant interacts with the organic phase, the stability of HIPEs is linked to the interfacial tension of the system. Ruckenstein and coworkers [109] showed that the maximum volume of hydrocarbon which could be incorporated in an o/w HIPE increased with increasing surfactant concentration, presumably due to a concomitant decrease in the interfacial tension. Solans et al. [9] claimed that the interfacial tension between the aqueous phase and the liquid-crystalline surfactant layer in their highly... 

Experiments on the stability of the HIPEs indicated that one of the most important factors was the solubility of the emulsifier in the continuous (formamide) phase. Thus, the higher the surfactant solubility, the more stable the emulsion. The emulsifier concentration was also important stability increased to a maximum, then decreased, with increasing surfactant concentration. Surprisingly, the HLB number did not appear to have much effect on the stability of the emulsions, over the range studied (11 to 14). This was attributed to the high concentration of emulsifier in the continuous phase, although the narrow HLB value range is probably also a factor. 

A plot of the temperatures required for clouding versus surfactant concentration typically exhibits a minimum in the case of nonionic surfactants (or a maximum in the case of zwitterionics) in its coexistence curve, with the temperature and surfactant concentration at which the minimum (or maximum) occurs being referred to as the critical temperature and concentration, respectively. This type of behavior is also exhibited by other nonionic surfactants, that is, nonionic polymers, // - a I k y I s u I Any lalcoh o I s, hydroxymethyl or ethyl celluloses, dimethylalkylphosphine oxides, or, most commonly, alkyl (or aryl) polyoxyethylene ethers. Likewise, certain zwitterionic surfactant solutions can also exhibit critical behavior in which an upper rather than a lower consolute boundary is present. Previously, metal ions (in the form of metal chelate complexes) were extracted and enriched from aqueous media using such a cloud point extraction approach with nonionic surfactants. Extraction efficiencies in excess of 98% for such metal ion extraction techniques were achieved with enrichment factors in the range of 45-200. In addition to metal ion enrichments, this type of micellar cloud point extraction approach has been reported to be useful for the separation of hydrophobic from hydrophilic proteins, both originally present in an aqueous solution, and also for the preconcentration of the former type of proteins. 

This was shown e.g. by investigating adsorption isotherms of Na dodecylbenzene-4-sulfonate and Na 4-hexadecyloxytolyl-2-sulfonate on various mineral surfaces differing from each other by the kind of PDFs86 . The potential value in relation to the surfactant concentration reached its maximum in the region of micelle formation and confirmed thus the shape of the adsorption isotherm. The presence of adsorption maxima is explained by a decrease in surfactant adsorption resulting from a desorption effect of micelles on the adsorption film, and by setting a three-component equilibrium (adsorption film - micelle - monomer) at concentrations CMC. This happens because of different ratios of the counter ions to the surfactant ions at the micelle and on the adsorption film. 

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 ... 

A useful way to compare the surface activity of different surfactants is in terms of their efficiency and effectiveness [30]. Efficiency measures the surfactant concentration required to achieve a certain surface tension, while effectiveness is measured by the maximum reduction of the surface tension that can be obtained for that particular surfactant. In the following discussion these terms will be used in this specific defined sense. 

Near the erne, the aggregation number corresponding to the maximum in the size distribution curve is lower than the value given by the above equation, but as the total surfactant concentration increases it approaches that value. Using the Ben-Naim-Stillinger expression for the free energy, we ohtain... 

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