Emulsion
Overview
An emulsionis a mixture of two or more liquids that are normally immiscible (un-blendable). Emulsions are part of a more general class of two-phase systems of matter
Matter
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...

 called colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...

s. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the continuous phase are liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

. In an emulsion, 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, index of refraction, and chemical composition...

) is dispersed
Dispersion (chemistry)
A dispersion is a system in which particles are dispersed in a continuous phase of a different composition . See also emulsion. A dispersion is classified in a number of different ways, including how large the particles are in relation to the particles of the continuous phase, whether or not...

 in the other (the continuous phase).
Encyclopedia
An emulsionis a mixture of two or more liquids that are normally immiscible (un-blendable). Emulsions are part of a more general class of two-phase systems of matter
Matter
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...

 called colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...

s. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the continuous phase are liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

. In an emulsion, 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, index of refraction, and chemical composition...

) is dispersed
Dispersion (chemistry)
A dispersion is a system in which particles are dispersed in a continuous phase of a different composition . See also emulsion. A dispersion is classified in a number of different ways, including how large the particles are in relation to the particles of the continuous phase, whether or not...

 in the other (the continuous phase). Examples of emulsions include vinaigrette
Vinaigrette
The word vinaigrette or vinegarette can refer to:*Vinaigrette, the salad dressing or sauce...

s, milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

, and some cutting fluids
Cutting fluid
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking and machining processes. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols , and air or other gases. They may be made from petroleum distillates, animal...

 for metal working. 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 resolution of the film...

 is an example of a colloid.

Structure and properties of emulsions

Emulsions, being liquid, do not exhibit a static internal structure; the droplets dispersed in the liquid matrix (the “dispersion medium”) are assumed to be statistically distributed
Probability distribution
In probability theory, a probability mass, probability density, or probability distribution is a function that describes the probability of a random variable taking certain values....

.

To understand the formation and properties of emulsions, consider that the dispersed phase exhibits a "surface" that is covered ("wetted") by a different "surface". These "surfaces" form an interface
Interface (chemistry)
An interface is a surface forming a common boundary among two different phases, such as an insoluble solid and a liquid, two immiscible liquids or a liquid and an insoluble gas. The importance of the interface depends on which type of system is being treated: the bigger the quotient area/volume,...

. Both surfaces have to be created, which requires an energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 input. Oil and water do not mix and usually separate from each other, forming two layers.

Appearance and properties

Emulsions contain both a dispersed and a continuous phase; the boundary between these phases is called the interface. Emulsions tend to have a cloudy appearance because the many phase interfaces
Phase boundary
The behavior of phase boundaries has been a developing subject of interest and an active research field in physics and mathematics for almost two centuries. One reason behind this is that phase boundaries naturally arise in many physical processes due to immiscibility of two or more substances with...

 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. In conventional use, this also includes deviation of...

 light as it passes through the emulsion. Emulsions appear white
White
White is a color, the perception of which is evoked by light that stimulates all three types of color sensitive cone cells in the human eye in nearly equal amounts and with high brightness compared to the surroundings. A white visual stimulation will be void of hue and grayness.White light can be...

 when all light is scattered equally. If the emulsion is dilute, higher-wavelength light will be scattered more and emulsion will appear 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 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...

r; this is the Tyndall effect
Tyndall effect
The Tyndall effect, also known as Tyndall scattering, is light scattering by particles in a colloid or particles in a fine suspension. It is named after the 19th century physicist John Tyndall. It is similar to Rayleigh scattering, in that the intensity of the scattered light depends on the fourth...

. If it is concentrated, the color will be distorted toward yellow
Yellow
Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, with no significant stimulation of the S cone cells. Light with a wavelength of 570–590 nm is yellow, as is light with a suitable mixture of red and green...

. This phenomenon is easily observable on comparing skimmed milk
Skimmed milk
Skimmed milk , or skim milk is made when all the cream is removed from whole milk .Sometimes only half the cream is removed, this is called semi-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. In the industrial production of cream this process is accelerated by using centrifuges called "separators"...

 (high concentration of milk fat). Microemulsion
Microemulsion
Microemulsions are clear, thermodynamically 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 dispersed phase, because light waves are scattered only if the droplets are nearly the same size as the light's wavelength.

Emulsions are unstable and, thus, do not form spontaneously. Energy input through shaking, stirring, homogenizing
Homogenization (chemistry)
Homogenization or homogenisation is any of several processes used to make a chemical mixture the same throughout.-Definition:Homogenization is intensive blending of mutually related substances or groups of mutually related substances to form a constant of different insoluble phases to obtain a...

, or spraying is needed to form an emulsion. Over time, emulsions tend to revert to the stable state of the phases comprising the emulsion; an example of this is seen in the separation of the oil and vinegar components of vinaigrette
Vinaigrette (food)
Vinaigrette is a mixture of olive oil and vinegar, sometimes flavored with herbs, spices, and other ingredients. It is used most commonly as a salad dressing,but also as a cold sauce or marinade.- Name :...

, an unstable emulsion that will quickly separate unless shaken continuously.

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 (see Emulsifier, below). In general, 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).

Instability

There are three types of instability in emulsions: flocculation
Flocculation
Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually...

, creaming
Creaming (chemistry)
Creaming, in the laboratory sense, is the migration of the dispersed phase of an emulsion, under the influence of buoyancy. The particles float upwards or sink, depending on how large they are and how much less dense or more dense they may be than the continuous phase, and also how viscous or how...

, and coalescence. Flocculation describes the process by which the dispersed phase comes out of suspension in flakes. Coalescence is another form of instability, when small droplets bump into each other and combine to form progressively larger droplets. Emulsions can also undergo creaming
Creaming (chemistry)
Creaming, in the laboratory sense, is the migration of the dispersed phase of an emulsion, under the influence of buoyancy. The particles float upwards or sink, depending on how large they are and how much less dense or more dense they may be than the continuous phase, and also how viscous or how...

, the migration of one of the substances to the top (or the bottom, depending on the relative densities of the two phases) of the emulsion under the influence of buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

, or under centripetal force
Centripetal force
Centripetal force is a force that makes a body follow a curved path: it is always directed orthogonal to the velocity of the body, toward the instantaneous center of curvature of the path. The mathematical description was derived in 1659 by Dutch physicist Christiaan Huygens...

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

 is used.

Surface active substances (surfactants) can increase the kinetic stability of emulsions so that the emulsion does not change significantly over time. A non-ionic surfactant solution can become self-contained under the force of its own surface tension, remaining in the shape of its previous container for some time after the container is removed.

“Emulsion stability refers to the ability of an emulsion to resist change in its properties over time.” D.J. McClements.

Technique monitoring physical stability

Multiple light scattering coupled with vertical scanning is the most widely used technique to monitor the dispersion state of a product, hence identifying and quantifying destabilisation phenomena. It works on concentrated emulsions without dilution. When light is sent through the sample, it is backscattered by the droplets. The backscattering intensity is directly proportional to the size and volume fraction of the dispersed phase. Therefore, local changes in concentration (Creaming
Creaming (chemistry)
Creaming, in the laboratory sense, is the migration of the dispersed phase of an emulsion, under the influence of buoyancy. The particles float upwards or sink, depending on how large they are and how much less dense or more dense they may be than the continuous phase, and also how viscous or how...

) and global changes in size (flocculation
Flocculation
Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually...

, coalescence
Coalescence (chemistry)
In chemistry, coalescence is a process in which two phase domains of the same composition come together and form a larger phase domain.-References:*...

) are detected and monitored.

Accelerating methods for shelf life prediction

The kinetic process of destabilisation can be rather long (up to several months or even years for some products), and it is often required for the formulator to use further accelerating methods in order to reach reasonable development time for new product design. Thermal methods are the most commonly used; this consists of increasing the emulsion temperature to accelerate destabilisation (below critical temperatures of phase inversion or chemical degradation). Temperature affects not only the viscosity but also interfacial tension in the case of non-ionic surfactants or, on a broader scope, interactions of forces inside the system. Storing an emulsion at high temperatures enables simulation of real-life conditions for a product (e.g., tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times.

Mechanical acceleration including vibration, centrifugation
Centrifugation
Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...

, and agitation are sometimes used. They subject the product to different forces that push the droplets against one another. However, some emulsions would never coalesce in normal gravity, while they do under higher forces. Moreover segregation of different populations of particles have been highlighted when using centrifugation and vibration.

Emulsifier

An emulsifier (also known as an emulgent) is a substance that stabilizes an emulsion by increasing its kinetic stability. One class of emulsifiers is known as surface active substances, or surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

s. Examples of food emulsifiers are egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...

 (in which the main emulsifying agent is lecithin
Lecithin
Lecithin is a generic term to designate any 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 .The word lecithin was originally coined in 1847 by...

), honey, and mustard
Mustard seed
Mustard seeds are the small round seeds of various mustard plants. The seeds are usually about 1 or 2 mm in diameter. Mustard seeds may be colored from yellowish white to black. They are important spices in many regional foods. The seeds can come from three different plants: black mustard , brown...

, where a variety of chemicals in the mucilage
Mucilage
Mucilage is a thick, gluey substance produced by most plants and some microorganisms. It is a polar glycoprotein and an exopolysaccharide.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...

 surrounding the seed hull act as emulsifiers; protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s and low-molecular-weight emulsifiers are common as well. Soy lecithin is another emulsifier and thickener. 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 phases. This type of emulsion was named after S.U...

. Both mayonnaise
Mayonnaise
Mayonnaise, , often abbreviated as mayo, is a sauce. It is a stable emulsion of oil, egg yolk and either vinegar or lemon juice, with many options for embellishment with other herbs and spices. Lecithin in the egg yolk is the emulsifier. Mayonnaise varies in color but is often white, cream, or pale...

 and Hollandaise sauce
Hollandaise sauce
Hollandaise sauce is an emulsion of egg yolk and butter, usually seasoned with lemon juice. In appearance it is light yellow and opaque, smooth and creamy. The flavor is rich and buttery, with a mild tang added by the lemon juice, yet not so strong as to overpower mildly-flavored foods.Hollandaise...

 are oil-in-water emulsions that are stabilized with egg yolk lecithin
Lecithin
Lecithin is a generic term to designate any 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 .The word lecithin was originally coined in 1847 by...

 or other types of food additives such as sodium stearoyl lactylate
Sodium stearoyl lactylate
Sodium stearoyl lactate and calcium stearoyl lactate are organic compounds used as a food additives in the List of food additives, Codex Alimentarius....

.

Detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...

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 usually liquid at room temperature ....

 and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

, thus stabilizing the interface between oil and water droplets in suspension. This principle is exploited in soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...

 to remove grease
Yellow grease
Yellow grease is derived from used cooking oil from the fast-food industry. It is used to feed livestock, and to make soap, make-up, clothes, rubber, detergents, and bio-diesel fuel....

 for the purpose of cleaning. Many different emulsifiers are used in pharmacy
Pharmacy
Pharmacy is the health profession that links the health sciences with the chemical sciences and it is charged with ensuring the safe and effective use of pharmaceutical drugs...

 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. Creams may be considered pharmaceutical products as even cosmetic creams are based on techniques developed by pharmacy and...

 and lotion
Lotion
A lotion is a low- to medium-viscosity, topical preparation intended for application to unbroken skin. By contrast, creams and gels have higher viscosity.Lotions are usually applied to external skin with bare hands, a clean cloth, cotton wool or gauze...

s. Common examples include emulsifying wax
Emulsifying wax
Emulsifying wax is a cosmetic emulsifying 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. It is used as an emulsion stabilizer, opacifying agent, and foam boosting surfactant, as well as an aqueous and...

, polysorbate 20, and ceteareth 20
Ceteareth
The INCI names ceteareth-n refer to polyoxyethylene ethers of a mixture of high molecular mass saturated fatty alcohols, mainly cetyl alcohol and stearyl alcohol...

. 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 observed when water is added to ouzo and other anise-flavored liqueurs and spirits, such as pastis, raki, arak and absinthe, forming a milky oil-in-water microemulsion...

, happens when water is poured into a strong alcoholic anise
Anise
Anise , Pimpinella anisum, also called aniseed, is a flowering plant in the family Apiaceae native to the eastern Mediterranean region and Southwest Asia. Its flavor resembles that of liquorice, fennel, and tarragon.- Biology :...

-based beverage, such as ouzo
Ouzo
Ouzo is an anise-flavored aperitif that is widely consumed in Greece and Cyprus, and a symbol of Greek culture.-History:Traditionally, tsipouro is said to have been the pet project of a group of 14th century monks living in a monastery on holy Mount Athos. One version of it is flavored with anise...

, pastis
Pastis
Pastis is an anise-flavored liqueur and apéritif from France, typically containing 40–45% alcohol by volume, although alcohol-free varieties exist.-Origins:...

, arak
Arak (distilled beverage)
Arak or Araq , is a highly alcoholic spirit from the anis drinks family. It is a clear, colorless, unsweetened anise-flavoured distilled alcoholic drink...

 or raki
Raki
-Alcoholic beverages:*Rakı, an anise-flavored spirit popular in Turkey*Any anise-flavored drink.-Fictional characters:*Raki, a character in the manga/anime series Claymore*Raki, a character in the game Ar tonelico II: Melody of Metafalica...

. The anisolic compounds, which are soluble in ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

, now form nano-size droplets and emulsify within the water. The colour of such diluted drink is opaque and milky.

In food

Oil-in-water emulsions are common in food:
  • Crema in espresso
    Espresso
    Espresso is a concentrated beverage brewed by forcing a small amount of nearly boiling water under pressure through finely ground coffee. Espresso is widely known throughout the world....

     – coffee oil in water (brewed coffee), unstable
  • Hollandaise sauce
    Hollandaise sauce
    Hollandaise sauce is an emulsion of egg yolk and butter, usually seasoned with lemon juice. In appearance it is light yellow and opaque, smooth and creamy. The flavor is rich and buttery, with a mild tang added by the lemon juice, yet not so strong as to overpower mildly-flavored foods.Hollandaise...

     – similar to mayonnaise
  • Mayonnaise
    Mayonnaise
    Mayonnaise, , often abbreviated as mayo, is a sauce. It is a stable emulsion of oil, egg yolk and either vinegar or lemon juice, with many options for embellishment with other herbs and spices. Lecithin in the egg yolk is the emulsifier. Mayonnaise varies in color but is often white, cream, or pale...

     – vegetable oil in lemon juice or vinegar, with egg yolk lecithin as emulsifier
  • Vinaigrette
    Vinaigrette
    The word vinaigrette or vinegarette can refer to:*Vinaigrette, the salad dressing or sauce...

     – vegetable oil in vinegar; if prepared with only oil and vinegar (without an emulsifier), yields an unstable emulsion
  • Homogenized milk – milk fat in water and milk proteins

In medicine

In pharmaceutics
Pharmaceutics
Pharmaceutics is the discipline of pharmacy that deals with all facets of the process of turning a new chemical entity into a medication able to be safely and effectively used by patients in the community. Pharmaceutics is the science of dosage form design...

, hairstyling
Hairstyling product
Hairstyling products are used to change the texture or shape of the hair, or to hold it in place in a certain style. Applied properly, most styling products will not damage the hair apart from drying it out; most styling products contain alcohols, which can dissolve oils...

, personal hygiene, and cosmetics
Cosmetics
Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...

, emulsions are frequently used. These are usually oil and water emulsions, but which is dispersed and which is continuous depends on the pharmaceutical formulation
Pharmaceutical formulation
Pharmaceutical formulation, in pharmaceutics, is the process in which different chemical substances, including the active drug, are combined to produce a final medicinal product.-Stages and timeline:...

. These emulsions may be called cream
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. Creams may be considered pharmaceutical products as even cosmetic creams are based on techniques developed by pharmacy and...

s, ointments, liniment
Liniment
Liniment , from the Latin linere, to anoint, is a medicated topical preparation for application to the skin. Preparations of this type are also called balm...

s (balms), paste
Paste (rheology)
In physics, a paste is a substance that behaves as a solid until a sufficiently large load or stress is applied, at which point it flows like a fluid. In rheological terms, a paste is an example of a Bingham plastic fluid....

s, film
Thin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....

s, or liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

s, depending mostly on their oil and water ratios and their route of administration
Route of administration
A route of administration in pharmacology and toxicology is the path by which a drug, fluid, poison, or other substance is taken into the body.-Classification:Routes of administration are usually classified by application location...

. The first 5 are topical
Topical
In medicine, a topical medication is applied to body surfaces such as the skin or mucous membranes such as the vagina, anus, throat, eyes and ears.Many topical medications are epicutaneous, meaning that they are applied directly to the skin...

 dosage form
Dosage form
-Introduction:Dosage forms are a mixture of active drug components and nondrug components. Depending on the method of administration they come in several types. These are liquid dosage form, solid dosage form and semisolid dosage forms. A Liquid dosage form is the liquid form of a dose of a...

s, and may be used on the surface of the skin
Human skin
The human skin is the outer covering of the body. In humans, it is the largest organ of the integumentary system. The skin has multiple layers of ectodermal tissue and guards the underlying muscles, bones, ligaments and internal organs. Human skin is similar to that of most other mammals,...

, transdermal
Transdermal
Transdermal is a route of administration wherein active ingredients are delivered across the skin for systemic distribution. Examples include transdermal patches used for medicine delivery, and transdermal implants used for medical or aesthetic purposes....

ly, ophthalmically
Eye drop
Eye drops are saline-containing drops used as a route to administer medication in the eye. Depending on the condition being treated, they may contain steroids, antihistamines, sympathomimetics, beta receptor blockers, parasympathomimetics, parasympatholytics, prostaglandins, non-steroidal...

, rectally or vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...

lly. A very liquidy emulsion may also be used oral
Oral administration
Oral administration is a route of administration where a substance is taken through the mouth.-Terminology:Per os is an adverbial phrase meaning literally from Latin "by mouth" or "by way of the mouth." The expression is used in medicine to describe a treatment that is taken orally. The...

ly, or it may be injected
Injection (medicine)
An injection is an infusion method of putting fluid into the body, usually with a hollow needle and a syringe which is pierced through the skin to a sufficient depth for the material to be forced into the body...

. Popular medicated emulsions include calamine lotion, cod liver oil
Cod liver oil
Cod liver oil is a nutritional supplement derived from liver of cod fish. It has high levels of the omega-3 fatty acids, EPA and DHA, and very high levels of vitamin A and vitamin D. It is widely taken to ease the symptoms of arthritis and for other health benefits...

, Polysporin
Polysporin
Polysporin is a line of antibiotic ointments produced by Johnson & Johnson used in the prevention of infection and speeding the healing of wounds. The original formulation contains bacitracin and polymyxin B....

, cortisol
Cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...

 cream, Canesten, and Fleet.

Microemulsions are used to deliver vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...

s and kill microbes. Typical emulsions used in these techniques are nanoemulsions of soybean oil
Soybean oil
Soybean oil is a vegetable oil extracted from the seeds of the soybean . It is one of the most widely consumed cooking oils. As a drying oil, processed soybean oil is also used as a base for printing inks and oil paints...

, with particles that are 400-600 nm in diameter. The process is not chemical, as with other types of antimicrobial
Antimicrobial
An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...

 treatments, but mechanical. The smaller the droplet, the greater the surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 and thus the greater the force to merge with other lipids. The oil is emulsified using a high shear mixer
High Shear Mixer
A high-shear mixer disperses, or transports, one phase or ingredient into a main continuous phase , with which it would normally be immiscible...

 with detergents to stabilize the emulsion, so, when they encounter the lipids in the membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 or envelope of bacteria
Cell envelope
The cell envelope is the cell membrane and cell wall plus an outer membrane, if one is present.Most bacterial cell envelopes fall into two major categories: Gram positive and Gram negative. These are differentiated by their Gram staining characteristics....

 or virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es, they force the lipids to merge with themselves. On a mass scale, this effectively disintegrates the membrane and kills the pathogen. This soybean oil emulsion does not harm normal human cells or the cells of most other higher organisms. The exceptions are sperm cells
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...

 and blood cells, which are vulnerable to nanoemulsions due to their membrane structures. For this reason, these nanoemulsions are not currently used intravenously. The most effective application of this type of nanoemulsion is for the disinfection
Disinfection
Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. Disinfection does not necessarily kill all microorganisms, especially nonresistant bacterial spores; it is less effective than sterilisation, which is an extreme physical...

 of surface
Surface
In mathematics, specifically in topology, a surface is a two-dimensional topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3 — for example, the surface of a ball...

s. Some types of nanoemulsions have been shown to effectively destroy HIV-1 and various tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

 pathogens, for example, on non-porous surfaces.

In firefighting

Emulsifying agents are effective at extinguishing fires on small thin layer spills of flammable liquids (Class B fire
Fire classes
In firefighting, fires are identified according to one or more fire classes. Each class designates the fuel involved in the fire, and thus the most appropriate extinguishing agent. The classifications allow selection of extinguishing agents along lines of effectiveness at putting the type of fire...

s). Such agents encapsulate the fuel in a fuel-water emulsion, thereby trapping the flammable vapors in the water phase. This emulsion is achieved by applying an aqueous
Aqueous solution
An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending aq to the relevant formula, such as NaCl. The word aqueous means pertaining to, related to, similar to, or dissolved in water...

 surfactant solution to the fuel through a high-pressure nozzle. Emulsifiers are not effective at extinguishing large (i.e., deep) fires involving liquid fuels, because the amount of agent needed for extinguishment is a function of the volume of the fuel, whereas agents such as aqueous film-forming foam (AFFF) need cover only the surface of the fuel to achieve vapor mitigation.

Uses

Emulsions are used in many major chemical industries. In the pharmaceutical industry, they are used to make medicines with a more appealing flavor and to improve value by controlling the amount of active ingredients. The most widely-used emulsions are non-ionic because they have low toxicity, but cationic emulsions are also used in some products because of their antimicrobial
Antimicrobial
An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...

 properties. Emulsions are also used in making many hair-care and skin-care products, such as oils and waxes. Water-based (latex) paints are oil-in-water emulsions.

See also

  • Emulsion dispersion
    Emulsion dispersion
    An emulsion dispersion is thermoplastics or elastomers suspended in a waterphase with help of emulsifiers.-Preparation:Emulsions are thermodynamically unstable liquid/liquid dispersions that are stabilized, in general, by surfactants...

  • Microemulsion
    Microemulsion
    Microemulsions are clear, thermodynamically 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 shearing a mixture comprising two immiscible liquid phases, one surfactant and one co-surfactant ....

  • Pickering emulsion
    Pickering emulsion
    A Pickering emulsion is an emulsion that is stabilized by solid particles which adsorb onto the interface between the two phases. This type of emulsion was named after S.U...

  • Water-in-water emulsion
    Water-in-water emulsion
    An emulsion is two immiscible liquids mixed together with small droplets of one liquid dispersed in the other liquid. This dispersion is usually not stable and all the droplets will “clump” together over time and forms two layers...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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