Within liquid-liquid extraction (LLE), extractants facilitate the separation of solutes between two immiscible phases. Due to their amphiphilic nature, extractant monomers may self-aggregate into structured molecular clusters, aggregates, or reverse micelles. This may occur in the organic diluent in the absence of extracted species from the aqueous phase, but is generally of importance when studying the nonequilibrium and equilibrium distribution of extracted hydrophilic solutes (water, acid, metal ions) that form a "polar core" of the reverse micelles. It is generally agreed that there is a specific concentration of solutes in the aqueous phase and extractant concentration in the organic phase that leads to a stable size distribution of reverse micelles, called the critical micelle concentration (CMC) or the critical aqueous concentration CAC. The CMC therefore separates the system into two regimes. Prior to the CMC, monomeric and small disordered aggregates with extracted solutes are dispersed in the organic phase. After the CMC, the extracted solutes primarily reside within the polar cores of the reverse micelles with an unchanging distribution of aggregate size with changing concentrations of acid, extractant or metal ion.