Mixed surfactant adsorption

Calculation examples of mixed surfactant adsorption The solid chosen as the model adsorbent was made up of a natural sand (specific area =380 cm2/g) mixed with 5% clay (Charentes kaolinite with specific area = 26.8 m2/g). This material was taken as a model of clayey sandstone reservoirs. 

The presence of mixed surfactant adsorption seems to be a factor in obtaining films with very viscous surfaces [411]. For example, in some cases the addition of a small amount of non-ionic surfactant to a solution of anionic surfactant can enhance foam stability due to the formation of a viscous surface layer, which is possibly a liquid crystalline surface phase in equilibrium with a bulk isotropic solution phase [25,110], In general, some very stable foams can be formed from systems in which a liquid crystal phase is present at lamella surfaces and in equilibrium with an isotropic interior liquid. If only the liquid crystal phase is present, stable foams are not produced. In this connection foam phase diagrams may be used to delineate compositions that will produce stable foams [25,110],... 

Nanoparticles of the semicondnctor titanium dioxide have also been spread as mono-layers [164]. Nanoparticles of TiOi were formed by the arrested hydrolysis of titanium iso-propoxide. A very small amount of water was mixed with a chloroform/isopropanol solution of titanium isopropoxide with the surfactant hexadecyltrimethylammonium bromide (CTAB) and a catalyst. The particles produced were 1.8-2.2 nm in diameter. The stabilized particles were spread as monolayers. Successive cycles of II-A isotherms exhibited smaller areas for the initial pressnre rise, attributed to dissolution of excess surfactant into the subphase. And BAM observation showed the solid state of the films at 50 mN m was featureless and bright collapse then appeared as a series of stripes across the image. The area per particle determined from the isotherms decreased when sols were subjected to a heat treatment prior to spreading. This effect was believed to arise from a modification to the particle surface that made surfactant adsorption less favorable. 

These assumptions are akin to those taken in account in the mixed adsorption model of Trogus (12). The difference between the two models lies in the relationship linking CMCs of single and mixed surfactants and monomer molar fractions Trogus used the empirical equation proposed by Mysels and Otter (13) in our model, the application of RST leads to an equation of the same type. 

Minssieux L., "Method for Adsorption Reduction of Mixed Surfactant Systems", Proc. 4th. Eur. EOR Symp., 1987, p. 293. 

Surfactants such as sulfated fatty alcohols may be hydrated to a higher extent than the fatty alcohols alone and thus stabilize o/w emulsions. The eombination of an anionic and a nonionic srrrfactant has proved to be partieularly effeetive, sinee the electrostatic repulsion forces between the ionie surfaetant moleeules at the interface are reduced by the incorporation of nonionic molecules, thus improving the emulsion stability. The combination of cetyl/stearyl sulfate (Lanette E) and eetyl/ stearyl alcohol (Lanette 0) to yield an emulsifying eetyl/stearyl aleohol (Lanette N) is an example of this approach. The polar properties of this srrrfactant mixtrrre are dominant, and o/w creams are formed. In contrast to w/o systems, the stabilizing effect of the surfactant mixtirre is not mainly due to adsorption at the interfaee. Instead, the mixed surfactants are highly hydrated and fonn a lamellar network, whieh is... 

The adsorption of mixed surfactants at the air—water interface (monolayer formation) is mechanistically very similar to mixed micelle formation. The mixed monolayer is oriented so that the surfactant hydrophilic groups are adjacent to each other. The hydrophobic groups are removed from the aqueous environment and are in contact with other hydrophobic groups or air. Therefore, the forces tending to cause monolayers to form are similar to those causing micelles to form and the thermodynamics and interactions between surfactants are similar in the two aggregation processes. 

Thermodynamic Study of the Surface Adsorption and Micelle Formation of Mixed Surfactants... 

Scamehorn et. al. (20) also presented a simple, semi—empirical method based on ideal solution theory and the concept of reduced adsorption isotherms to predict the mixed adsorption isotherm and admicellar composition from the pure component isotherms. In this work, we present a more general theory, based only on ideal solution theory, and present detailed mixed system data for a binary mixed surfactant system (two members of a homologous series) and use it to test this model. The thermodynamics of admicelle formation is also compared to that of micelle formation for this same system. 

Mixed Admicelles. The total sur-factant adsorption o-f the two pure sur-factants and mixtures thereo-f on alumina are shown in Figure 3. The mixtures are at constant surFactant ratio in the Feed or initial solution, but not necessarily in the Final equilibrium solution. The concentration on the abscissa is the equilibrium concentration. The individual surFactant adsorption isotherms For the pure surFactants and in the mixtures are shown in Figures 4 and 5. The experiments were run at the same swamping electrolyte concentration as were the CMC data. 

A few papers have been published recently on the problem of surfactant adsorption maxima on solids in the region of the CMC (1-5). Scamehorn et al. (1,2) and Trogus et al. (3) expTTined the origin of these maxima by various radios of the surfactant solution to the solid, in connection with isomeric impurity of the surfactant. Ananthapadmanabhan and Soniasundaran (4) examined critically the presence of such maxima from the viewpoint of various proposed adsorption mechanisms. They have shown that a mechanism including micellar exclusion, mixed micelle formation and properties of solids, such as the pore size, cannot explain satisfac-... 

Adsorption of Two Surfactants. We now denote a quantity valid at the onset of micellization in the equilibrium mixed surfactant solution by the superscript c. Thus, the chemical potential of surfactant i in the mixed solution or in the mixed surface phase at the onset of micellization is given by... 

Critical Micelle Concentration. In order to demonstrate the analogy between our treatment of mixed adsorption and earlier treatments of mixed micellization, we will briefly review the thermodynamics of mixed micelles. The thermodynamics of formation of ideal mixed micelles by two surfactants has been treated by Lange and Beck (9 ) and Cling (10). Rubingh ( ) extended the treatment to account for interactions between the surfactants, essentially by writing the cmc in the mixed surfactant solution as. 

It would be of scientific interest to study the adsorption of mixed surfactant systems showing positive deviations from ideality, as has been discussed for mixed micelles and monolayers. 

Miller, R., Alahverdjieva, V.S., Fainerman, V.B. (2008). Thermodynamics and rheology of mixed protein-surfactant adsorption layers. Soft Matter, 4, 1141-1146. 

Miller, R., Fainerman, V.B., Makievski, A.V., Kragel, J., Grigoriev, D.O., Kazakov, V.N., Sinyachenko, O.V. (2000a). Dynamics of protein and mixed protein + surfactant adsorption layers at the water-fluid interface. Advances in Colloid and Interface Science, 86, 39-82. 

Surfactant adsorption and its effect on chromatographic flow can sometimes be exploited to control the distance from the injection well at which different surfactants mix. Thus, if the transport rates of two different chemicals are known, the slower moving one can be injected first, followed by the faster moving one at an appropriate later time. The distance from the well at which the two mix will be determined by the delay time between the injections and the difference in the transport velocities. 

Wilson and co-workers developed a statistical mechanical model for single component surfactant adsorption (29-31) and expanded it to a binary system (2,3). Different adsorption curves were generated by varying the Van der Waals interaction parameters. The mixed adsorption equations that were developed were very complex and were not applied to experimental data. 

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