Surfactants mixed

Fig. IV 23. Penetration of cholesterol monolayers by CTAB (hexadecyl-trimethylam-monium bromide. [From D. M. Alexander, G. T. Barnes, M. A. McGregor, and K. Walker, Phenomena in Mixed Surfactant Systems, in J. F. Scamehom, ed., ACS Symposium Series 311, p. 133, 1986 (Ref. 269). Copyright 1986, American Chemical Society.]...

Small micelles in dilute solution close to the CMC are generally beheved to be spherical. Under other conditions, micellar materials can assume stmctures such as oblate and prolate spheroids, vesicles (double layers), rods, and lamellae (36,37). AH of these stmctures have been demonstrated under certain conditions, and a single surfactant can assume a number of stmctures, depending on surfactant, salt concentration, and temperature. In mixed surfactant solutions, micelles of each species may coexist, but usually mixed micelles are formed. Anionic-nonionic mixtures are of technical importance and their properties have been studied (38,39). 

Mixed Surfactant Systems, edited by Keizo Ogino and Masahiko Abe... 

The net result is that detergency performance for mixed active formulations is not so drastically reduced by high water hardness conditions. The improvement in detergency by mixed surfactant systems can be seen not only in under-... 

FIG. 2 CMC of linear alkylbenzenesulfonate-a-olefmsulfonate (LABS-AOS) mixed surfactant system. (From Ref. 3.)... 

C. I. Chiwetelu, V. Homof, G. H. Neale, and A. E. George. Use of mixed surfactants to improve the transient interfacial tension behaviour of heavy oil/alkaline systems. Can J Chem Eng, 72(3) 534-540, June 1994. 

Defoaming Theory and Industrial Applications, edited by P. R. Garrett Mixed Surfactant Systems, edited by Keizo Ogino and Masahiko Abe Coagulation and Flocculation Theory and Applications, edited by Bohusiav DobiaD Biosurfactants Production Properties Applications, edited by Naim Kosaric Wettability, edited by John C. Berg... 

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. 

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. 

Xia J. et alii, "Effects of Different Distributions of Lyophobic Chain Length on the Interfacial Properties of Nonaethoxylated Fatty Alcohol" in "Phenomena in Mixed Surfactant Systems", J.F. Scamehom, Ed. 1986, ACS Stmposium Series 311, Wash. 

Scamehom, J.F. Phenomena in Mixed Surfactant Systems American Chemical Society, Symposium Series Washington, DC 1986. 

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... 

Among the purposes of this paper is to report the results of calorimetric measurements of the heats of micellar mixing in some nonideal surfactant systems. Here, attention is focused on interactions of alkyl ethoxylate nonionics with alkyl sulfate and alkyl ethoxylate sulfate surfactants. The use of calorimetry as an alternative technique for the determination of the cmc s of mixed surfactant systems is also demonstrated. Besides providing a direct measurement of the effect of the surfactant structure on the heats of micellar mixing, calorimetric results can also be compared with nonideal mixing theory. This allows the appropriateness of the regular solution approximation used in models of mixed micellization to be assessed. 

Calorimetric measurements can be used to obtain heats of mixing between different surfactant components in nonideal mixed micelles and assess the effects of surfactant structure on the thermodynamics of mixed micellization. Calorimetry can also be successfully applied in measuring the erne s of nonideal mixed surfactant systems. The results of such measurements show that alkyl ethoxylate sulfate surfactants exhibit smaller deviations from ideality and interact significantly less strongly with alkyl ethoxylate nonionics than alkyl sulfates. 

The mixed cmc behavior of these (and many other) mixed surfactant systems can be adequately described by a nonideal mixed micelle model based on the psuedo-phase separation approach and a regular solution approximation with a single net interaction parameter B. However, the heats of micellar mixing measured by calorimetry show that the assumptions of the regular solution approximation do not hold for the systems investigated in this paper. This suggests that in these cases the net interaction parameter in the nonideal mixed micelle model should be interpreted as an excess free energy parameter. 

The spread mixed lipid monolayer studies provide information about the packing and orientation of such molecules at the water interface. These interfacial characteristics affect many other systems. For instance, mixed surfactants are used in froth flotation. The monolayer surface pressure of a pure surfactant is measured after the injection of the second surfactant. From the change in n, the interaction mechanism can be measured. The monolayer method has also been used as a model biological membrane system. In the latter BLM, lipids are found to be mixed with other lipidlike molecules (such as cholesterol). Hence, mixed monolayers of lipids + cholesterol have been found to provide much useful information on BLM. The most important BLM and temperature melting phenomena is the human body temperature regulation. Normal body temperature is 37°C (98°F), at which all BLM function efficiently. 

All formulators use mixed surfactants, particularly since Griffin s HLB concept and its associated mixing rule was introduced 50 years ago as a yardstick for hydrophilicity. There are essentially two reasons either the commercial products they use are already mixtures, or the proper surfactant property is not attainable with a commercial product, and it is attempted by mixing available species. 

There is no available modeling of this effect, and only some qualitative trends can be provided by the reports on mixed surfactant micelUzation. 

And rez JM, Bracho CL, Sereno S, Salager JL (1993) Effect of surfactant concentration on the properties of anionic-nonionic mixed surfactant-oU-brine systems. Colloid Surface A 76 249-256... 

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