emulsion

1 (chemistry) a colloid in which both phases are liquids; "an oil-in-water emulsion"

2 a light-sensitive coating on paper or film; consists of fine grains of silver bromide suspended in a gelatin [syn: photographic emulsion]

see Emulsion

English

Noun

1. a stable suspension of small droplets of one liquid in another with which it is immiscible

   Mayonnaise is an emulsion where egg is used to keep oil and water mixed.

2. a colloid in which both phases are liquid
3. the coating of photosensitive silver halide grains in a thin gelatine layer on a photographic film

Translations

Derived terms

• solid emulsion
• emulsify

Finnish

Noun

emulsion

Used in pharmaceuticals and in cosmetics(skin care)

An emulsion(IPA: /ɪˈmʌlʃən/) 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, magmas and cutting fluid for metal working. In butter and margarine, oil surrounds droplets of water (a water-in-oil emulsion). In milk and cream, water surrounds droplets of oil (an oil-in-water emulsion). In certain types of magma, globules of liquid NiFe may be dispersed within a continuous phase of liquid silicates. Emulsification is the process by which emulsions are prepared.

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

Operation

Emulsions tend to have a cloudy appearance, because the many phase interfaces (the boundary between the phases is called the interface) scatter light that passes through the emulsion. Emulsions are unstable and thus do not form spontaneously. Energy input through shaking, stirring, homogenizers, or spray processes are needed to form an emulsion. Over time, emulsions tend to revert to the stable state of oil separated from water. Surface active substances (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 colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion tends to imply that both the dispersed and the continuous phase are 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.

Emulsifier

An emulsifier (also known as an emulgent) is a substance which stabilizes an emulsion, frequently a surfactant. Examples of food emulsifiers are egg yolk (where the main emulsifying chemical is lecithin), honey and mustard, where a variety of chemicals in the mucilage surrounding the seed hull act as emulsifiers; proteins and low-molecular weight emulsifiers are common as well. In some cases, particles can stabilize emulsions as well through a mechanism called Pickering stabilization. Both mayonnaise and hollandaise sauce are oil-in-water emulsions that are stabilized with egg yolk lecithin. Detergents are another class of surfactant, and will chemically interact with both oil and water, thus stabilising the interface between oil or water droplets in suspension. This principle is exploited in soap to remove grease for the purpose of cleaning. A wide variety of emulsifiers are used in pharmacy to prepare emulsions such as creams and lotions.

• Photo emulsion
• Water-in-water emulsion
• Photographic emulsion
• Interface and colloid science

References

External links

• Microfluidic Production of Monodispersed Submicron EmulsionsThrough Filtration and Sorting of Satellite Drops 2005-652
• Video images of the process of membrane emulsification
• Video image of monodisperse droplets produced by membrane emulsification
• Company website of Nanomi, specialized in membrane emulsification
• Explanation of the process of membrane emulsification
• Medicine at Michigan
• Veterinary Applications
• Dispersion Technology

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