Critical micelle concentration
From Wikipedia, the free encyclopedia
In chemistry, the critical micelle concentration (CMC) is defined as the concentration of surfactants in free solution in equilibrium with surfactants in aggregated form.
There are several theoretical definitions of CMC. One well-known definition is that CMC is the total concentration of surfactants under the conditions:
- if C = CMC, (d3F/dCt3) = 0
- F = a[micelle] + b[monomer]: function of surfactant solution
- Ct: total concentration
- a, b: proportional constants
Therefore, CMC depends on the method of measuring the samples, since a and b depend on the properties of the solution such as conductance and photochemical characteristics. When the degree of aggregation is monodispersion, the CMC is not related to the method of measurement. On the other hand, when the degree of aggregation is multidispersion, CMC is related to both the method of measurement and the dispersion.
The self-organisation of the molecules of surfactants and lipids depends on the concentration of the lipid present in solution. Below the critical micelle concentration the lipids form a single layer on the liquid surface and are dispersed in solution. At the first critical micelle concentration (CMC-I), the lipids organise in spherical micelles, at the second critical micelle concentration (CMC-II) into elongated pipes, and at the lamellar point (LM or CMC-III) into stacked lamellae of pipes. The CMC depends on the chemical composition, mainly on the ratio of the head area and the tail length.
