colloidal chemistry Interface and colloid science is an interdisciplinary intersection of branches of chemistry, physics, nanoscience and other fields dealing with ''colloids'', heterogeneous systems consisting of a mechanical mixture of particles between 1 nm ...

, an aggregation number is a description of the number of

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s present in a

micelle A micelle () or micella () ( 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 colloidal system). ...

once the

critical micelle concentration In colloidal chemistry, 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) has been reached. In more detail, it has been defined as the average number of

surfactant Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a Blend word, blend of "surface-active agent", coined in ...

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 In chemical thermodynamics, isothermal titration calorimetry (ITC) is a physical technique used to determine the Conjugate variables (thermodynamics), thermodynamic parameters of interactions in Solution (chemistry), solution. ITC is the only tec ...

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 probe, a quencher and a known

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number 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