An aggregation number is a description of the number of molecules present in a

micelle A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated coll ...

once the

critical micelle concentration In colloidal and surface chemistry, the critical micelle concentration (CMC) is defined as the concentration of surfactants above which micelles form and all additional surfactants added to the system will form micelles. The CMC is an important c ...

(CMC) has been reached. In more detail, it has been defined as the average number of surfactant monomers in a spherical micelle.Moroi, Yoshikiyo. Micelles: theoretical and applied aspects. Springer Science & Business Media, 1992. The aggregation number of micelles can be determined by

isothermal titration calorimetry Isothermal titration calorimetry (ITC) is a physical technique used to determine the thermodynamic parameters of interactions in solution. It is most often used to study the binding of small molecules (such as medicinal compounds) to larger macro ...

when the aggregation number is not too high.N.E. Olesen. Journal of Colloid and Interface Science. 453 (2015) 79-89Bouchemal, 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. Another classical experiment to determine the mean aggregation number would involve the use of a

luminescent Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a crystal ...

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.

References

Colloidal chemistry {{physical-chemistry-stub