Dictionary:

emulsion

  (ĭ-mŭl'shən)

1. A suspension of small globules of one liquid in a second liquid with which the first will not mix: an emulsion of oil in vinegar.
2. A photosensitive coating, usually of silver halide grains in a thin gelatin layer, on photographic film, paper, or glass.

[New Latin ēmulsiō, ēmulsiōn-, from Latin ēmulsus, past participle of ēmulgēre, to milk out : ē-, ex-, ex- + mulgēre, to milk.]

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A dispersion of one liquid in a second immiscible liquid. Since the majority of emulsions contain water as one of the phases, it is customary to classify emulsions into two types: the oil-in-water (O/W) type consisting of droplets of oil dispersed in water, and the water-in-oil (W/O) type in which the phases are reversed. The continuous liquid is referred to as the dispersion medium, and the liquid which is in the form of droplets is called the disperse phase.

A stable emulsion consisting of two pure liquids cannot be prepared; to achieve stability, a third component, an emulsifying agent, must be present. Generally, the introduction of an emulsifying agent will lower the interfacial tension of the two phases. A large number of emulsifying agents are known; they can be classified broadly into several groups. The largest group is that of the soaps, detergents, and other compounds whose basic structure is a paraffin chain terminating in a polar group. Some solid powders can act as emulsifiers by being wetted more by one phase than by the other. Whichever phase shows the greater wetting power will become the dispersion medium. Many naturally occurring emulsions, such as milk or rubber latex, are stabilized by proteins. Egg yolk proteins stabilize mayonnaise and salad dressing. Certain hydrophilic colloids such as gum arabic or gelatin also stabilize water-in-oil emulsions by a similar mode of action.

Emulsions may be prepared readily by shaking together the two liquids or by adding one phase drop by drop to the other phase with some form of agitation, such as irradiation by ultrasonic waves of high intensity. In industry, emulsification is accomplished by means of emulsifying machines.

The breaking of emulsions is necessary in many industrial operations, for example, in the separation of water-in-oil emulsions in the petroleum industry and in product recovery from emulsions produced by the steam distillation of organic liquids. Emulsions may be broken by (1) addition of multivalent ions of charge opposite to the emulsion droplet, (2) chemical action (addition of acids to emulsions stabilized by soaps), (3) freezing, (4) heating, (5) aging, (6) centrifuging, (7) application of high-potential alternating electric fields, and (8) treatment with ultrasonic waves of low intensity. See also Colloid; Soap.

An intimate mixture of two immiscible liquids (for example oil and water), one being dispersed in the other in the form of fine droplets. They will stay mixed only as long as they are stirred together, unless an emulsifying agent is added.

[ih-MUHL-shuhn] A mixture of one liquid with another with which it cannot normally combine smoothly-oil and water being the classic example. Emulsifying is done by slowly (sometimes drop-by-drop) adding one ingredient to another while at the same time mixing rapidly. This disperses and suspends minute droplets of one liquid throughout the other. Emulsified mixtures are usually thick and satiny in texture. Mayonnaise (an uncooked combination of oil, egg yolks and vinegar or lemon juice) and hollandaise (a cooked mixture of butter, egg yolks and vinegar or lemon juice) are two of the best-known emulsions.

A colloidal dispersion of one liquid in another. See also suspension.

For more information on emulsion, visit Britannica.com.

1. A mixture of liquids insoluble in one another, in which one is suspended in the other in the form of minute globules.
2. A mixture in which solid particles are suspended in a liquid in which they are insoluble, as a mixture of bitumen and water, with uniform dispersion of the bitumen globules. The cementing action needed in roofing and waterproofing takes place as the water evaporates.

A mixture of two immiscible liquids, one being dispersed throughout the other in small droplets; a colloid system in which both the dispersed phase and the dispersion medium are liquids. Margarine, cold cream and various medicated ointments are emulsions. In some emulsions the suspended particles tend to join together and settle out; hence the container must be shaken each time the emulsion is used.

• x-ray e. — radiation-sensitive coating of an x-ray film consisting of a suspension of finely divided grains of silver halide in gelatin.

A. Two immiscible liquids, not emulsified; B. An emulsion of Phase II dispersed in Phase I; C. The unstable emulsion progressively separates; D. The surfactant (purple outline) positions itself on the interfaces between Phase A and Phase B, stabilizing the 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, 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 (water-in-oil 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) 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.

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 pathogens such as bacteria and viruses. The process is not chemical, as with other types of anti-pathogenic treatments, but physical. The smaller the droplet, the greater the 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 surfactant. Examples of food emulsifiers are egg yolk (where the main emulsifying chemical is the phospholipid lecithin), 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.

20 ml ampule of 1% propofol emulsion suitable for intravenous injection. The manufacturers emulsify the lipid soluble propofol in a mixture of water, soy oil and egg lecithin.

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

• Photo emulsion
• Water-in-water emulsion
• Photographic emulsion

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
• Explanation of the process of membrane emulsification
• 
  Medicine at Michigan
• Veterinary Applications
• Dispersion Technology

References

Category

Interface and Colloid Science

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - emulsion
v. tr. - male med emulsion

Nederlands (Dutch)
emulsie, het mengsel dat op filmpjes zit

Français (French)
n. - émulsion
v. tr. - peindre avec de la peinture à émulsion

Deutsch (German)
n. - Emulsion
v. - mit Dispersionsfarbe streichen

Ελληνική (Greek)
n. - (χημ.) γαλάκτωμα

Italiano (Italian)
emulsione, emulsionare

Português (Portuguese)
n. - emulsão (f)

Русский (Russian)
эмульсия

Español (Spanish)
n. - emulsión
v. tr. - pintar con pintura emulsionada

Svenska (Swedish)
n. - emulsion

中文（简体） (Chinese (Simplified))
乳状液, 乳剂, 擦乳状液

中文（繁體） (Chinese (Traditional))
n. - 乳狀液, 乳劑
v. tr. - 擦乳狀液

한국어 (Korean)
n. - 젖 상태의 액체(유상액)
v. tr. - 이멀젼 페인트로 칠하다

日本語 (Japanese)
n. - 乳濁液, 感光乳剤, 乳剤

العربيه (Arabic)
‏(الاسم) المستحلب‏

עברית (Hebrew)
n. - ‮התפזרות של נוזל בתוך אחר, תחליב, אמולסיה, תערובת של תרכובת כסף וג'לטין לציפוי לוחות או סרטי צילום‬
v. tr. - ‮צבע בצבע תחליב‬

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