Microemulsion
Microemulsions are unclear, thermodynamically stable, isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous phase may contain salt(s) and/or other ingredients, and the "oil" may actually be a complex mixture of different hydrocarbons and olefins. In contrast to ordinary emulsions, microemulsions form upon simple mixing of the components and do not require the high shear conditions generally used in the formation of ordinary emulsions. The three basic types of microemulsions are direct (oil dispersed in water, o/w), reversed (water dispersed in oil, w/o) and bicontinuous.
In ternary systems such as microemulsions, where two immiscible phases (water and ‘oil’) are present with a surfactant, the surfactant molecules may form a monolayer at the interface between the oil and water, with the hydrophobic tails of the surfactant molecules dissolved in the oil phase and the hydrophilic head groups in the aqueous phase.
Micro-emulsion: Dispersion made of water, oil, and surfactant(s) that is an
isotropic and thermodynamically stable system with dispersed domain diameter varying
approximately from 1 to 100 nm, usually 10 to 50 nm.
Note 1: In a micro-emulsion the domains of the dispersed phase are either globular
or interconnected (to give a bicontinuous micro-emulsion).
Note 2: The average diameter of droplets in macro-emulsion (usually referred to as an
“emulsion”) is close to one millimeter (i.e., 10−3 m). Therefore, since micro- means 10−6
and emulsion implies that droplets of the dispersed phase have diameters close to 10−3 m,
the micro-emulsion denotes a system with the size range of the dispersed phase in the
10−6 × 10−3 m = 10−9 m range.
Note 3: The term “micro-emulsion” has come to take on special meaning. Entities of
the dispersed phase are usually stabilized by surfactant and/or surfactant-cosurfactant
(e.g., aliphatic alcohol) systems.
...
Wikipedia