Thermodynamic Aspects of Mixed Micelles and Solubilization

The preceding discussion has been confined to two-component systems, amphiphile-water. In a large number of cases of practical importance one adds one (or more) additional component(s). Depending on the nature of the additive one can recognize different effects. If it is an amphiphile it is usually found that the micelles which form in the solution are of mixed composition. Under the assumption that the amphiphiles mix ideally in the micellar aggregate, Shinoda177 has derived expressions for the effective CMC of the amphiphile mixture. For nonionics 

When a semipolar, e.g., an alcohol, or a nonpolar, e.g., an alkane, substance is added to a micellar system the additives are solubilized in the micelles. The presence of a solubilized molecule in the micelle reduces the activity of the amphiphile in the aggregate. It is thus a natural consequence that the CMC (with respect to amphiphile concentration) is lowered. A strict thermodynamic analysis4,181 18 2) gives, in analogy with Henry s law  

Measurements of thermodynamic parameters can provide important information on the chemical nature of the solubilization process. The partial molar volumes of a hydrocarbon in a micellar solution is very similar to the value obtained for a hydrocarbon phase, and differs significantly from that obtained in water39,183.  

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