nanoemulsion

A nanoemulsion is an ordinary oil-and-water emulsion in which the dispersed droplets have been beaten down to nanometre size, typically under about 200 nanometres. Because the droplets are far smaller than the wavelength of visible light, the milky cloudiness of a normal emulsion fades and the liquid often looks clear or faintly bluish. A fat-soluble drug rides inside these tiny oil droplets, ready for delivery.

Shrinking the droplets brings real advantages: the enormous combined surface area speeds up release and absorption of the drug, and the small size resists the creaming and droplet-merging that ruin coarse emulsions. Nanoemulsions are used for intravenous nutrition and drug injection, as well as oral and topical products, and are made either by high-energy methods like high-pressure homogenisation or by low-energy self-emulsifying methods.

It is important to be honest about stability. A nanoemulsion is only kinetically stable, not thermodynamically stable — it is a metastable system that, given enough time, still tends toward separation. This separates it from a true microemulsion, which despite its name is thermodynamically stable, often has even smaller droplets, and forms spontaneously without strong mixing.