Synergism mixed micelle formation

Non-ideal solution theory is used to calculate the value of a parameter, S, that measures the interaction between two surfactants in mixed monolayer or mixed micelle formation. The value of this parameter, together with the values of relevant properties of the individual, pure surfactants, determines whether synergism will exist in a mixture of two surfactants in aqueous solution. 

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. 

Figure 2. Synergism in surface tension reduction efficiency (Ci2 < C ° or 2°) or in mixed micelle formation...

Synergism in mixed micelle formation. Synergism in this respect is present when the critical micelle concentration of any mixture is lower than that of either pure surfactant. This is illustrated in Figure 2. 

By mathematical treatment similar to that for synergism in surface tension reduction efficiency, we have found that the conditions for synergism in mixed micelle formation are ... 

At the point of maximum synergism in mixed micelle formation, M... 

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 ... 

Table II. Synergism in Mixed Micelle Formation at 25 C System 0 2 25 V 8 17 ° 2 4 4° ...

Figure 4. Synergism in mixed micelle formation for some binary surfactant mixtures. gOH mixtures...

The last two free-energy contributions involve only the surfactant heads. The steric contribution, gst, accounts for steric interactions between the surfactant heads at the micellar interface. This contribution can be responsible for synergism in mixed micelle formation if the heads of the two-surfactant types have different sizes, as illustrated by the large grey heads and small black heads ii Figure 12.14. The steric contribution depends only on the size of the surfactant heads. 

In many products or processes, two surfactants are used together to improve the properties of the system. In some cases, the two surfactants interact in such fashion that the CMC of the mixture (Cf2) is always intermediate in value between those of the two components Cf, C2). In other cases they interact in such fashion that Cf2 at some ratio of the two surfactants is less than either Cf1 or C2. When the latter case occurs, the system is said to exhibit synergism in mixed micelle formation. In still other cases, Cf2 at some ratio of the two surfactants may be larger than either Cf or C2. Here the system is said to exhibit antagonism (negative synergism) in mixed micelle formation. 

III.B. Synergism or Antagonism (Negative Synergism) in Mixed Micelle Formation in Aqueous Medium... 

Analogous expressions have been derived (Rosen, 1986) for the existence of synergism in mixed micelle formation in the presence of a second liquid phase and for the conditions at the point of maximum synergism. 

The relations between synergism (or antagonism) in the fundamental properties of mixed monolayer formation at an interface or mixed micelle formation in solution and synergism in various practical applications of surfactants is still a relatively unexplored area. Some studies have probed this area, but much remains to be known. 

Fig. 2 Synergism in surface tension reduction efficiency or in mixed micelle formation. Surfactant 1. Surfactant 2. 0 Mixture of surfactants 1 and 2 at mole fraction a in the solution phase. Synergism in surface tension reduction efficiency Cn < C , C . Synergism in mixed micelle formation < CT, Cf...

We may consider precipitation in these systems in the context of competitive aggregate formation between micelles and precipitate. Even systems forming ideal mixed micelles can exhibit synergisms in salinity/hardness tolerance in such systems, the more components present, the higher the tolerance. This is the reason that mixtures of isomeric surfactants generally have Krafft temperatures considerably lower than those of the individual compounds (90). 

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