Surfactant potential

Diamond electrodes thus open up new opportunities for work under extreme conditions, including very high anodic potentials, surfactant-rich... 

The point of zero charge of the reservoir minerals, their physical structure, the surfactant equivalent weight and structure, and the structure of the electrical double layer at the solid/solution interface appear to be major factors determining the mechanism of adsorption and potential surfactant losses in surfactant flooding. 

Microorganisms are capable to produce a great variety of products with excellent surface-active properties. However, its use in certain applications depends on the production and purification costs for specific activities, if compared to the corresponding synthetic surfactants. Thus, the last works are concentrated in the identification of potentials surfactants, in the evaluation of their properties, and in the optimization of the fermentative processes for their production [4]. 

A clear correlation has been observed between limiting surface tension ycmc and surfactant performance in water-in-C02 microemulsions, as measured by the phase transition pressure Ptnms- These results have important implications for the rational design of C02-philic surfactants. Studies of aqueous solutions are relatively easy to carry out, and surface tension measurements can be used to screen target compounds expected to exhibit enhanced activity in CO2. Therefore, potential surfactant candidates can be identified before making time-consuming phase stability measurements in high-pressure CO2. 

Table XI-1 (from Ref. 166) lists the potential-determining ion and its concentration giving zero charge on the mineral. There is a large family of minerals for which hydrogen (or hydroxide) ion is potential determining—oxides, silicates, phosphates, carbonates, and so on. For these, adsorption of surfactant ions is highly pH-dependent. An example is shown in Fig. XI-14. This type of behavior has important applications in flotation and is discussed further in Section XIII-4.

Fig. XI-13. Adsorption isotherms for SNBS (sodium p-3-nonylbenzene sulfonate) (pH 4.1) and DPC (dodecyl pyridinium chloride) (pH 8.0) on mtile at approximately the same surface potential and NaCl concentration of O.OlAf showing the four regimes of surfactant adsorption behavior, from Ref. 175. [Reprinted with permission from Luuk K. Koopal, Ellen M. Lee, and Marcel R. Bohmer, J. Colloid Interface Science, 170, 85-97 (1995). Copyright Academic Press.]...

The adsorption appears to be into the Stem layer, as was illustrated in Fig. V-3. That is, the adsorption itself reduces the f potential of such minerals in fact, at higher surface coverages of surfactant, the potential can be reversed, indicating that chemical forces are at least comparable to electrostatic ones. The rather sudden drop in potential beyond a certain concentration suggested to... 

If an ionic surfactant is present, the potentials should vary as shown in Fig. XIV-5c, or similarly to the case with nonsurfactant electrolytes. In addition, however, surfactant adsorption decreases the interfacial tension and thus contributes to the stability of the emulsion. As discussed in connection with charged monolayers (see Section XV-6), the mutual repulsion of the charged polar groups tends to make such films expanded and hence of relatively low rr value. Added electrolyte reduces such repulsion by increasing the counterion concentration the film becomes more condensed and its film pressure increases. It thus is possible to explain qualitatively the role of added electrolyte in reducing the interfacial tension and thereby stabilizing emulsions. 

The Donnan effect acts to exclude like-charged substrate ions from a charged surface region, and this exclusion, as well as the concentration of oppositely charged ions, can be expressed in terms of a Donnan potential pD. Thus for a film of positively charged surfactant ions S one can write... 

Assume diat die chemical potential, p., of surfactant in aggregates of size N in equilibrium widi one anodier is unifonii. One may dierefore write... 

The standard chemical potentials are approximately tire same if tire surfactant in each aggregate sees nearly tire same interaction witli tire solvent. This simplifying assumption tlien gives... 

Herein Pa and Pb are the micelle - water partition coefficients of A and B, respectively, defined as ratios of the concentrations in the micellar and aqueous phase [S] is the concentration of surfactant V. ai,s is fhe molar volume of the micellised surfactant and k and k , are the second-order rate constants for the reaction in the micellar pseudophase and in the aqueous phase, respectively. The appearance of the molar volume of the surfactant in this equation is somewhat alarming. It is difficult to identify the volume of the micellar pseudophase that can be regarded as the potential reaction volume. Moreover, the reactants are often not homogeneously distributed throughout the micelle and... 

The current or potential iadustrial appHcations of microemulsions iaclude metal working, catalysis, advanced ceramics processiag, production of nanostmctured materials (see Nanotechnology), dyeiag, agrochemicals, cosmetics, foods, pharmaceuticals, and biotechnology (9,12—18). Environmental and human-safety aspects of surfactants have begun to receive considerable attention (19—21). 

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