Emulsion



 

An emulsion is a mixture of two immiscible (unblendable) substances. One substance (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include butter and margarine, milk and cream, espresso, mayonnaise, the photo-sensitive side of photographic film, and cutting fluid for metal working. In butter and margarine, a continuous liquid phase surrounds droplets of water (a water-in-oil emulsion). In milk and cream, oil is dispersed within a continuous water phase (an oil-in-water emulsion). Emulsification is the process by which emulsions are prepared.


Emulsions tend to have a cloudy appearance, because the many phase interfaces (the boundary between the phases is called the interface) surfactants) can increase the kinetic stability of emulsions greatly so that, once formed, the emulsion does not change significantly over years of storage. Homemade oil and vinegar salad dressing is an example of an unstable emulsion that will quickly separate unless shaken continuously. This phenomenon is called coalescence, and happens when small droplets recombine to form bigger ones. Fluid emulsions can also suffer from creaming, the migration of one of the substances to the top of the emulsion under the influence of buoyancy or centripetal force when a centrifuge is used.

Emulsions are part of a more general class of two-phase systems of matter called liquid.

There are three types of emulsion instability: flocculation, where the particles form clumps; creaming, where the particles concentrate towards the surface (or bottom, depending on the relative density of the two phases) of the mixture while staying separated; and breaking and coalescence where the particles coalesce and form a layer of liquid.

Emulsion is also a term used in the oil field as untreated well production that consists primarily of crude oil and water.

Nanoemulsion

Nanoemulsion is a type of emulsion in which the sizes of the particles in the dispersed phase are defined as less than 1000 nanometers.

In medicine, a nanoemulsion of soybean oil to create drops of 400-600 nanometers in diameter will kill many surface tension and thus the greater the force to merge with other lipids. The oil is emulsified with detergents to stabilize the emulsion (the droplets won't merge with one another), so when they encounter lipids on a bacterial membrane or a virus envelope, they force the lipids to merge with themselves. On a mass scale, this effectively disintegrates the membrane and kills the pathogen.

Remarkably, the soybean oil emulsion does not harm normal human cells nor the cells of most other higher organisms. The exceptions are sperm cells and blood cells, which are vulnerable to nanoemulsions due to their membrane structures. For this reason, nanoemulsions of this type are not yet ready to be used intravenously.

The most effective application of this type of nanoemulsion is for the disinfection of surfaces. Some types of nanoemulsions have been shown to effectively destroy HIV-1 and various tuberculosis pathogens, for example, on non-porous surfaces.

Emulsifier

An emulsifier (also known as an emulgent) is a substance which stabilizes an emulsion, frequently a lotions.  

Whether an emulsion turns into a water-in-oil emulsion or an oil-in-water emulsion depends on the volume fraction of both phases and on the type of emulsifier. Generally, the Bancroft rule applies: emulsifiers and emulsifying particles tend to promote dispersion of the phase in which they do not dissolve very well; for example, proteins dissolve better in water than in oil and so tend to form oil-in-water emulsions (that is they promote the dispersion of oil droplets throughout a continuous phase of water).

See also

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