Micelles and microemulsions

Micelles and microemulsions are liquid dispersions containing surfactant aggregate,s, in micellar dispersions, thc aggregates are made of surfactant only and are usually dispersed in water. In microemulsions, the aggregates are much larger: They have large liquid cores [oil in oil in water (o/w) microemulsions, water in w/o microemulsions] surrounded by a surfactant monolayer that stabilizes the dispersion. Micelles may be swollen by oils to a generally limited extent (of the order of one oil molecule per surfactant molecule). The large degree of swelling reached in microemulsions can only be obtained with suitable surfactants. In many cases, the micellar aggregates are spherical, but they can also be tubular. In a few cases, they can grow very long and entangle like polymers. Surfactant molecules do not always associate into micelles and, in some cases, do not form closed structures: They associate into extended flat lamellae in the so-called lamellar or L~ phases, which are smectic liquid crystalline phases; in other phases, called L3, the lamellae are distorted and interconnected, and the structure is sponge-like and isotropic. Microemulsions, like micellar phases, are phases without macroscopic order. The microemulsion droplets are usually spherical, but some examples of tubular structures have been reported. Sponge-like structures, in which the oil and water microdomains are multiply connected, also exist, but they are less frequent than droplets structures. Sponge-like structures are frequently discussed in the literature, because they correspond to a maximum in the