In addition to the chemical structure, the concentration also has a decisive influence on the surface tension. The equilibrium value of the surface tension decreases as the number of surfactant molecules accumulating at the surface increases. It achieves its final value when the surface is completely occupied and offers no place for further molecules. If the concentration is further increased from this point then the surfactant molecules will accumulate within the solution and form aggregates, the so-called “micelles”.

The concentration at which this effect occurs is known as the “critical micelle formation concentration” (CMC). It is an important characteristic for surfactants.

This means that methods for measuring the dynamic surface tensions should only be used above the CMC. In such a case the concentration only influences the chronological function of the surface tension and no longer has any influence on its static value. The following illustration shows the measuring ranges of static and dynamic methods (e.g. the bubble pressure method):