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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 micelle temperature. [citation needed]
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]
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.
Micellar solutions form when the concentration of amphiphile exceeds the critical micelle concentration (CMC) or critical aggregation concentration (CAC), which is when there are enough amphiphiles in the solution to clump together to form micells.
Bottle of 20% sodium dodecyl sulfate in distilled water for use in the laboratory. The critical micelle concentration (CMC) in water at 25 °C is 8.2 mM, [1] and the aggregation number at this concentration is usually considered to be about 62. [3] The micelle ionization fraction (α) is around 0.3 (or 30%). [4]
An amphiphilic behavior can be observed for water and an organic solvent or between two organic solvents. Note 2: Polymeric micelles have a much lower critical micellar concentration (CMC) than soap (0.0001 to 0.001 mol/L) or surfactant micelles, but are nevertheless at equilibrium with isolated macromolecules called unimers.
Above the critical micelle concentration, the anions organize into a micelle, in which they form a sphere with the polar, hydrophilic heads of the sulfate portion on the outside (surface) of the sphere and the nonpolar, hydrophobic tails pointing inwards towards the center. The water molecules around the micelle in turn arrange themselves ...
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.