1. n. 
An ordered aggregate of surfactant molecules formed when the surfactant concentration in a solution reaches a critical point, thus lowering the free energy of the system. Within an aqueous phase, the molecules in a micelle organize such that the hydrophilic head group is the outermost part of the micelle and the hydrophobic tail group is inside the micellar surface. Within an oil phase a reverse, or inverse, micelle can form: The surfactant molecules then organize such that the hydrophobic tail group is outermost, and the hydrophilic head group is inside the surface. A micelle can solubilize oil in water; a reverse micelle can solubilize water in oil.