Critical micelle concentration

In chemistry, describes the critical micelle concentration, or CMC ( critical micelle concentration engl. ), the concentration of surfactant at which micelles form. It is an important characterizing property of surfactants used in detergents, soaps, etc..

Behavior of surfactants in various concentrations

At a concentration of surface-active substances ( such as surfactants ) below the CMC are the molecules freely and individually in the surrounding liquid or they position themselves at the free surface. This applies to concentrations below the CMC, the surface tension of the liquid decreases with increasing concentration of the surfactants. If the CMC is reached, start the surfactant molecules to form micelles. If the concentration is then raised further, increasing the number of micelles formed. As surfactants now take no further influence on the free surface of the liquid, the surface tension is - constant above the CMC - in an ideal system.

Models

There are various approaches for describing the theoretical CMC. For example, in a model, the CMC obtained if and only if

Notes on various systems

CMC is the critical concentration as the " bulk phase" of liquid is defined. For most systems, this reference is of no relevance, especially when the number of surfactant molecules in the liquid itself (in the " bulk phase " ) with respect to the number of surfactant molecules at the surface is very large. Thus, it can be determined in these cases, the concentration of the surfactants of the light amount of the added surfactant and the liquid volume ( or mass). In some special cases, such as when the free surface is very large compared to the volume of liquid, however, the surfactant concentration in the " bulk" of the method described no longer be determined. To bind, for example, in bubble columns large amounts of surfactants to the rising bubbles so that the local concentration can fall into the liquid below the CMC. This method can also be used to remove surfactants from solution ( flotation). Similar considerations can be performed for emulsions.