Binary surfactants

The corresponding monomer/micelle equilibria can be dealt with by the regular solution theory (RST), as shown in particular by Rubingh in 1979 (1). The application of this theory to numerous binary surfactant systems (2 - 4) has followed and led to a set of coherent results (5). 

Table I. Values of the Net Interaction Parameter 3 for Some Binary Surfactant Mixtures (from Ref. 3) ...

In order to illustrate the eFFect oF micellar nonidealities oF mixing on total surFactant monomer concentrations and micelle compositions in a system at the CHC, consider a hypothetical binary surFactant pair, A and B. Assume CMCa = 1 mli and CMCb = 2 mil. For a equimolar mixture oF A and B as monomer, the values oF Cn and micelle compositions are tabulated in Table I at various values oF W/RT. 

Table 1. Total Monomer Concentrations and Micellar Compositions For a Binary SurFactant System at Various Deviations From Ideality...

Consider the formation of a mixed micelle in aqueous solution from a binary surfactant solution consisting of a nonionic and an anionic surfactant. The process is depicted as the aggregation of ng molecules of nonionic surfactant B, of n molecules of anionic surfactant A", and in addition there will be counterions, C" ", of the anionic surfactant in the amount of an where a is the fraction of the counterions associated or bound with the surfactant anions in the micelle. The process as depicted is... 

The equation which formally describes the micellization of binary surfactants is... 

A mass action model (MAM) with monodisperse aggregation number N which depends on the micelle mole fraction x and the counterion binding parameter /3(x) has been developed for binary surfactants either ionic/ionic or nonionic/ionic. 

Figure 4. Surfactant 1 monomer (cj), surfactant 2 monomer (C2), counterion (cj +j and micelle (c ,) inventories and micelle compositions (x) for binary surfactants with c /c = 3.0, A = 0, B = 0,...

Figure 3 shows the total surfactant concentration required to attain a given surface tension (reduction) as a function of a in a number of binary surfactant systems. It illustrates the require-... 

Figure 3. Synergism in surface tension reduction efficiency for some binary surfactant mixtures.

In the case of surface adsorption, at constant surface tension ofsolutions, an equation of the same form as equation 12 is obtained for the binary surfactant mixture system (15,16) ... 

It is evident that the non-ideal solution theory of surface adsorption and micellization is a convenient and useful tool for obtaining the surface and the micelle compositions and for studing the molecular interaction in the binary surfactant system. 

Binary surfactant mixtures have traditionally been modeled using the pseudophase-separation approach, in which the micelles are treated as a separate, inLnite phase in equilibrium with the... 

Additional values otp have been tabulated for many binary surfactant mixtures (Rosen, 1978). 

Eads, C. D., and L. C. Robosky. 1999. NMR studies of binary surfactant mixture thermodynamics Molecular size model for asymmetric activity coef cierttangmuir15 2661-2668. 

Sarmoria, C., S. Puvvada, and D. Blankschtein. 1992. Prediction of critical micelle concentrations of nonideal binary surfactant mixturelangmuir8 2690-2697. 

Shiloach, A., and D. Blankschtein. 1998a. Predicting micellar solution properties of binary surfactant mixtures. Langmuir14 1618-1636. 

Treiner, C., M. Nortz, C. Vaution, and F. Puisieux. 1988. Micellar solubilization in aqueous binary surfactant systems Barbituric acids in mixed anionjcnonionic or cationiGf nonionic mixturesJ. Coll. Interf. 

Previous work has shown that binary surfactant systems containing Dowfax 8390 and the branched hydrophobic surfactant AOT can form Winsor III systems with both PCE and decane whereas DOWFAX 8390 by itself cannot (Wu et. al. 1999). This binary surfactant system was used in conjunction with hydrophobic octanoic acid to help with phase behavior and lessen the required concentration of CaCl2. Since this formulation is rather complicated, questions about field robustness arise. Thus, for the phase behavior studies presented here, we used the simple binary system of the nonionic TWEEN 80 and the branched hydrophobic AOT, and we optimized the NaCl concentration to give the Winsor Type III system. The lesser electrolyte concentration requirement for the binary TWEEN 80/ AOT system helps to decrease the potential for undesirable phase behavior such as surfactant precipitation, thereby increasing surfactant system robustness. 

Figure 24. Synergistic effect on detergency in binary surfactant systems (test method modified Leenerts condition total surfactant concentration—0.04 wt...

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