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An emulsion (IPA: /?'m?l??n/) is a mixture of two immiscible (unblendable) liquids. One liquid (the dispersed phase
Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, refractive index, and chemical composition....
) is dispersed
Dispersion

Dispersion can refer to:...
 in the other (the continuous phase
Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, refractive index, and chemical composition....
). Many emulsions are oil/water emulsions, with dietary fats being one common type of oil encountered in everyday life. Examples of emulsions include butter
Butter

Butter is a dairy product made by churning fresh or fermentation cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications such as baking, sauce making, and frying....
 and margarine
Margarine

Margarine , as a generic term, can indicate any of a wide range of butter substitutes. In many parts of the world, margarine has become the best-selling table spread, although butter and olive oil also command large market shares....
, milk
Milk

Milk is an opaque white liquid produced by the mammary glands of female mammals . It provides the primary source of nutrition for newborn mammals before they are able to digestion other types of food....
 and cream, and vinaigrettes
Vinaigrette (food)

Vinaigrette is a mixture of vinegar and oil, often flavored with herbs, spices, and other ingredients. There are many ways to prepare Vinaigrette but a basic recipe is to slowly add 3 parts of oil at room temperature to 1 part of vinegar until it emulsifies into a smooth sauce....
; the photo-sensitive side of photographic film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the film....
, magma
Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
s and cutting fluid
Cutting fluid

Cutting fluids are various fluids that are used in machining to cool and lubricate the cutting tool. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, and mists....
 for metal working.






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An emulsion (IPA: /?'m?l??n/) is a mixture of two immiscible (unblendable) liquids. One liquid (the dispersed phase
Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, refractive index, and chemical composition....
) is dispersed
Dispersion

Dispersion can refer to:...
 in the other (the continuous phase
Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, refractive index, and chemical composition....
). Many emulsions are oil/water emulsions, with dietary fats being one common type of oil encountered in everyday life. Examples of emulsions include butter
Butter

Butter is a dairy product made by churning fresh or fermentation cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications such as baking, sauce making, and frying....
 and margarine
Margarine

Margarine , as a generic term, can indicate any of a wide range of butter substitutes. In many parts of the world, margarine has become the best-selling table spread, although butter and olive oil also command large market shares....
, milk
Milk

Milk is an opaque white liquid produced by the mammary glands of female mammals . It provides the primary source of nutrition for newborn mammals before they are able to digestion other types of food....
 and cream, and vinaigrettes
Vinaigrette (food)

Vinaigrette is a mixture of vinegar and oil, often flavored with herbs, spices, and other ingredients. There are many ways to prepare Vinaigrette but a basic recipe is to slowly add 3 parts of oil at room temperature to 1 part of vinegar until it emulsifies into a smooth sauce....
; the photo-sensitive side of photographic film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the film....
, magma
Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
s and cutting fluid
Cutting fluid

Cutting fluids are various fluids that are used in machining to cool and lubricate the cutting tool. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, and mists....
 for metal working. In butter and margarine, fat surrounds droplets of water (a water-in-oil emulsion). In milk and cream, water surrounds droplets of fat (an oil-in-water emulsion). In certain types of magma, globules of liquid NiFe
NiFe

NiFe or Nife is a general shorthand expression for a mixture of nickel and iron . NiFe is used to describe Nickel-iron battery, various chemical reactions that involve a nickel-iron catalyst or component, and in geology to describe the general composition of the Structure of the Earth#Core....
 may be dispersed within a continuous phase of liquid silicate
Silicate

A silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. This definition is broad enough to include species such as hexafluorosilicate , [SiF6]2-, but the silicate species that are encountered most often consist of silicon with oxygen as the ligand...
s. Emulsification is the process by which emulsions are prepared.

Emulsion is also a term used in the oil field
Oil field

An oil field is a region with an abundance of oil wells extracting petroleum from below ground. Because the oil reservoirs typically extend over a large area, possibly several hundred kilometres across, full exploitation entails multiple wells scattered across the area....
 as untreated well
Oil well

An oil well is a general term for any boring through the Earth's surface designed to find and produce petroleum Petroleum hydrocarbons. Usually some natural gas is produced along with the oil, and a well designed to produce mainly or only gas may be termed a gas well....
 production that consists primarily of crude oil and water.

Emulsions tend to have a cloudy appearance, because the many phase interfaces (the boundary between the phases is called the interface) scatter
Scattering

Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles,are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass....
 light that passes through the emulsion. Emulsions are unstable and thus do not form spontaneously. Energy input through shaking, stirring, homogenizing, or spray processes are needed to form an emulsion. Over time, emulsions tend to revert to the stable state of the phases comprising the emulsion. Surface active substances (surfactant
Surfactant

Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids....
s) can increase the kinetic stability of emulsions greatly so that, once formed, the emulsion does not change significantly over years of storage. Vinaigrette
Vinaigrette (food)

Vinaigrette is a mixture of vinegar and oil, often flavored with herbs, spices, and other ingredients. There are many ways to prepare Vinaigrette but a basic recipe is to slowly add 3 parts of oil at room temperature to 1 part of vinegar until it emulsifies into a smooth sauce....
 is an example of an unstable emulsion that will quickly separate unless shaken continuously. This phenomenon is called coalescence
Coalescence (meteorology)

Coalescence is the process by which two or more droplets or particles merge during contact to form a single daughter droplet . It can take place in many processes, ranging from meteorology to astrophysics....
, and happens when small droplets recombine to form bigger ones. Emulsions can also suffer from creaming
Creaming (chemistry)

Creaming, in the laboratory sense, is the migration of a substance in an emulsion, under the influence of buoyancy, to the top of a sample while the particles of the substance remain separated, as compared to flocculation or breaking ....
, the migration of one of the substances to the top of the emulsion under the influence of buoyancy
Buoyancy

In physics, buoyancy is the upward force that keeps things afloat. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body....
 or centripetal force
Centripetal force

The centripetal force is the external force required to make a body follow a curved path. Hence centripetal force is a kinematic force requirement, not a particular kind of force like gravity or electromagnetism....
 when a centrifuge
Centrifuge

A centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis....
 is used.

Emulsions are part of a more general class of two-phase systems of matter called colloid
Colloid

A colloid is a type of chemical mixture where one substance is dispersed evenly throughout another. The particles of the dispersed substance are only suspended in the mixture, unlike a solution, where they are completely dissolved within....
s. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion tends to imply that both the dispersed and the continuous phase are liquid
Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
.

There are three types of emulsion instability: flocculation
Flocculation

Flocculation is a process where a solute comes out of solution in the form of floc or flakes. The action differs from Precipitation in that the solute coming out of solution does so at a concentration generally below its solubility limit in the liquid....
, where the particles form clumps; creaming
Creaming

Creaming may refer to:In cooking and baking* In cooking, the process of creamed* In baking, the process of creaming In chemistry...
, 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
Coalescence

Coalescence may refer to:* Coalescence , the merging of genetic lineages backwards time to a most recent common ancestor* Coalescence , the merging of two or more words into one...
 where the particles coalesce and form a layer of liquid.

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
Bancroft rule

The Bancroft rule states: "The phase in which an emulsifier is more soluble constitutes the continuous phase."It was named after Wilder Dwight Bancroft, an American physical chemist....
 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).

The basic color of emulsions is white
White

White is a color, the Color vision#Physiology of color perception which is evoked by light that stimulates all three types of color sensitive cone cells in the human eye in near equal amount and with high brightness compared to the surroundings....
. If the emulsion is dilute, the Tyndall effect
Tyndall effect

The Tyndall effect is an effect of light scattering by colloid particles or particles in Suspension . It is named after the 19th century Irish scientist John Tyndall....
 will scatter the light and distort the color to blue
Blue

Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440?490 Nanometre....
; if it is concentrated, the color will be distorted towards yellow
Yellow

Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, but does not significantly stimulate the S cone cells; that is, light with much red and green but not very much blue....
. This phenomenon is easily observable on comparing skimmed milk (with no or little fat) to cream
Cream

Cream is a dairy product that is composed of the higher-butterfat layer skimmed from the top of milk before homogenization. In un-homogenized milk, over time, the lighter fat rises to the top....
 (high concentration of milk fat). Microemulsion
Microemulsion

Microemulsions are clear, stable, isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous Phase may contain salt and/or other ingredients, and the "oil" may actually be a complex mixture of different hydrocarbons and olefins....
s and nanoemulsions tend to appear clear due to the small size of the disperse phase.

Emulsifier

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

Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids....
. Examples of food emulsifiers are egg yolk
Egg yolk

An egg yolk is the part of an Egg which serves as the food source for the developing embryo inside. Prior to fertilization the yolk together with the germinal disc is a single Cell ....
 (where the main emulsifying chemical is lecithin
Lecithin

Lecithin is any of a group of yellow-brownish fatty substances occurring in animal and plant tissues, and in egg yolk, composed of phosphoric acid, choline, fatty acids, glycerol, glycolipids, triglycerides, and phospholipids ....
), honey, and mustard
Mustard seed

Mustard seeds are the small seeds of the various mustard plants. The seeds are about 2 mm in diameter, and may be colored from yellowish white to black....
, where a variety of chemicals in the mucilage
Mucilage

Mucilage is a chemical polarity glycoprotein; an polysaccharide; a polymer produced by most plants and some microorganisms.It occurs in various parts of nearly all classes of plant, usually in relatively small percentages, and is frequently associated with other substances, such as tannins and alkaloids....
 surrounding the seed hull act as emulsifiers; protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s and low-molecular weight emulsifiers are common as well. In some cases, particles can stabilize emulsions as well through a mechanism called Pickering stabilization
Pickering emulsion

A Pickering emulsion is an emulsion that is stabilized by solid particles which adsorb onto the interface between the two phase s. This type of emulsion was named after its discoverer, Percival Spencer Umfreville Pickering, who first described the phenomenon in 1907....
. Both mayonnaise and Hollandaise sauce
Hollandaise sauce

Hollandaise sauce is an emulsion of butter and lemon juice using egg yolks as the emulsifying agent, usually seasoned with salt and a little black pepper or cayenne pepper....
 are oil-in-water emulsions that are stabilized with egg yolk lecithin. Detergent
Detergent

A detergent is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning....
s are another class of surfactant, and will physically interact with both oil
Cooking oil

Cooking oil is purified fat of plant origin, which is liquid at room temperature.Some of the many different kinds of edible Vegetable fats and oilss include: olive oil, palm oil, soybean oil, canola oil, pumpkin seed oil, corn oil, sunflower oil, safflower oil, peanut oil, grape seed oil, sesame oil, argan oil and rice bran oil....
 and water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
, thus stabilizing the interface between oil or water droplets in suspension. This principle is exploited in soap
SOAP

SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks....
 to remove grease
Yellow grease

Yellow grease is a term from the rendering . It usually means used frying Cooking oils from deep fryers and restaurants' grease traps. It can also refer to lower-quality grades of tallow from rendering plants....
 for the purpose of cleaning. A wide variety of emulsifiers are used in pharmacy
Pharmacy

Pharmacy is the health profession that links the health sciences with the chemistrys, and it is charged with ensuring the safe and effective use of medication....
 to prepare emulsions such as creams
Cream (pharmaceutical)

A cream is a topical preparation usually for application to the skin. Creams for application to mucus membranes such as those of the rectum or vagina are also used....
 and lotion
Lotion

A lotion is a low- to medium-viscosity, topical preparation intended for application to unbroken skin; creams and gels have a higher viscosity. Most lotions are oil-in-water emulsions using a substance such as Cetearyl alcohol to keep the emulsion together, but water-in-oil lotions are also formulated....
s. Common examples include emulsifying wax
Emulsifying wax

Emulsifying wax is a cosmetics emulsion ingredient. The ingredient name is often followed by the initials NF, indicating that it conforms to the specifications of the National Formulary....
, cetearyl alcohol
Cetearyl alcohol

Cetostearyl alcohol, cetearyl alcohol or cetylstearyl alcohol is a mixture of fatty alcohols, consisting predominantly of cetyl and stearyl alcohols and is classified as a fatty alcohol....
, polysorbate 20, and ceteareth 20
Ceteareth

The INCI names Ceteareth-n refer to polyethylene glycol ethers of a mixture of high molecular mass saturated fatty alcohols . The number n indicates the average number of etyhlene oxide residues in the polyoxyethylene chain....
.

Sometimes the inner phase itself can act as an emulsifier, and the result is nanoemulsion - the inner state disperses into nano-size droplets within the outer phase. A well-known example of this phenomenon, the ouzo effect
Ouzo effect

The ouzo effect is a phenomenon seen when water is added to ouzo and other :Category:Anise liqueurs and spirits: a cloudy oil-in-water microemulsion forms....
, happens when water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 is poured in a strong alcoholic anise
Anise

is a flowering plant in the family Apiaceae native to the eastern Mediterranean region and southwest Asia known for its flavor that resembles licorice, fennel, and tarragon....
-based beverage, such as ouzo
Ouzo

Ouzo is an anise-flavored distilled beverage that is widely consumed in Greece. It is similar to pastis , Sambuca , Mastika , Raki , Salmiakki Koskenkorva or Arak ....
, pastis
Pastis

Pastis is an anise-flavored liqueur and ap?ritif from France, typically containing 40?45% alcohol by volume, although Ethanol-free varieties exist....
 or raki
Raki

Raki may mean:* An alternate name for Rangi and Papa, the sky father in the South Island dialect of Maori*Rakia or Raki, alcoholic beverage, popular throughout the Balkans....
. The anisolic compounds, which are soluble in ethanol
Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatility , flammable, colorless liquid....
, now form nano-sized droplets and emulgate within the water. The colour of such diluted drink is opaque and milky.

In medicine

Propofol
In medicine, microscopic emulsions are used to deliver vaccines and kill microbes. Typically, the emulsions used in these techniques are nanoemulsions of soybean oil, with particles 400-600 nanometers in diameter. The process is not chemical, as with other types of anti-pathogenic treatments, but physical. The smaller the droplet, the greater the surface tension
Surface tension

Surface tension is an attractive property of the surface of a liquid. It is what causes the surface portion of liquid to be attracted to another surface, such as that of another portion of liquid ....
 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
Virus

A virus is a Optical microscope#Limitations of light microscopes infectious agent that is unable to grow or reproduce outside a host cell . Viruses infect all cellular life....
, 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
Spermatozoon

A sperm, from the ancient Greek word sp???a and and more commonly known as a sperm cell, is the ploidy cell that is the male gamete. It Fertilization an ovum to form a zygote....
 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
Tuberculosis

Tuberculosis is a common and often deadly infectious disease caused by mycobacterium, mainly Mycobacterium tuberculosis . Tuberculosis usually attacks the lungs but can also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, the gastrointestinal system, bones, joints, and even the...
 pathogens, for example, on non-porous surfaces.

See also

  • Emulsion dispersion
    Emulsion dispersion

    An emulsion dispersion is thermoplastics or elastomers suspension in a waterphase with help of emulsifiers....
  • Microemulsion
    Microemulsion

    Microemulsions are clear, stable, isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous Phase may contain salt and/or other ingredients, and the "oil" may actually be a complex mixture of different hydrocarbons and olefins....
  • Miniemulsion
    Miniemulsion

    A miniemulsion is a special case of emulsion. A miniemulsion is obtained by shear a mixture comprising two Miscible liquid phases, one surfactant and one co-surfactant ....