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The critical micelle concentration (CMC) is the exact concentration of surfactants at which aggregates become thermodynamically soluble in an aqueous solution. Below the CMC there is not a high enough density of surfactant to spontaneously precipitate into a distinct phase. [7]
After reaching the CMC, the surface tension remains relatively constant or changes with a lower slope. The value of the CMC for a given dispersant in a given medium depends on temperature, pressure, and (sometimes strongly) on the presence and concentration of other surface active substances and electrolytes. Micelles only form above critical ...
In colloid science, a micellar solution consists of a dispersion of micelles (small particles) in a solvent (most usually water). Micelles are made of chemicals that are attracted to both water and oily solvents, known as amphiphiles. In a micellar solution, some amphiphiles are clumped together and some are dispersed.
When the concentration of a surfactant in solution reaches its critical micelle concentration (CMC), it forms micelles which are aggregates of the monomers. The CMC is different for each surfactant, as is the number of monomers which make up the micelle, termed the aggregation number (AN). [5]
The molecules will be forced to remain in the aqueous phase when there are no more vacancies for them to stay on the surface. At this point, the surface tension is maximally lowered and is termed as the critical micelle concentration (CMC). [21] The lower the CMC, the more efficient the wetting solution is in reducing surface tension.
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]
For most lyotropic systems aggregation occurs only when the concentration of the amphiphile exceeds a critical concentration (known variously as the critical micelle concentration (CMC) or the critical aggregation concentration (CAC)). At very low amphiphile concentration, the molecules will be dispersed randomly without any ordering.
Upon reaching the CMC, the dissolved surfactant concentration reaches a maximum, where the surfactant monomers will aggregate to form nanometer sized micelles. [40] Due to this potential for micelle formation, three steps can be utilized when analyzing the adsorption of the surfactants to the droplet’s interface. [40]