A micellar solution consists of a dispersion of micelle

Micelle

A micelle is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single tail regions in the micelle centre. This phase is...

s in a solvent

Solvent

A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

 (most usually water). Micelles consist of aggregated amphiphiles, and in a micellar solution these are in equilibrium with free, unaggregated amphiphiles. Micellar solutions form when the concentration of amphiphile exceeds the critical micellar concentration (CMC)

Critical micelle concentration

In colloidal and surface chemistry, the critical micelle concentration is defined as the concentration of surfactants above which micelles form and almost all additional surfactants added to the system go to micelles....

 or critical aggregation concentration - CAC, and persist until the amphiphile concentration becomes sufficiently high to form a lyotropic liquid crystal

Lyotropic liquid crystal

A liquid crystalline material is called lyotropic if phases having long-ranged orientational order are induced by the addition of a solvent. Historically the term was used to describe materials composed of amphiphilic molecules. Such molecules comprise a water-loving 'hydrophilic' head-group ...

phase.

Although micelles are often depicted as being spherical, they can be cylindrical or oblate depending on the chemical structure of the amphiphile. Micellar solutions are isotropic phases.