In colloidal chemistry, an aggregation number is a description of the number of molecules present in a micelle once the critical micelle concentration (CMC) has been reached.
In more detail, it has been defined as the average number of surfactant monomers in a spherical micelle.
[1] The aggregation number of micelles can be determined by isothermal titration calorimetry when the aggregation number is not too high.
[2][3] Another classical experiment to determine the mean aggregation number would involve the use of a luminescent probe, a quencher and a known concentration of surfactant.
If the concentration of the quencher is varied, and the CMC of the surfactant known, the mean aggregation number can be calculated.