# Aggregation number

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In [colloidal chemistry](/source/Interface_and_colloid_science), an **aggregation number** is a description of the number of [molecules](/source/Molecule) present in a [micelle](/source/Micelle) once the [critical micelle concentration](/source/Critical_micelle_concentration) (CMC) has been reached. In more detail, it has been defined as the average number of [surfactant](/source/Surfactant) monomers in a spherical micelle.[1]

The aggregation number of micelles can be determined by [isothermal titration calorimetry](/source/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](/source/Luminescent) probe, a [quencher](/source/Quenching_(fluorescence)) and a known [concentration](/source/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.

## References

1. Moroi, Yoshikiyo. Micelles: theoretical and applied aspects. Springer Science & Business Media, 1992.

1. N.E. Olesen. Journal of Colloid and Interface Science. 453 (2015) 79-89

1. Bouchemal, Kawthar, et al. "What can isothermal titration microcalorimetry experiments tell us about the self-organization of surfactants into micelles?." Journal of Molecular Recognition 23.4 (2010): 335-342.

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