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An emulsion is a
mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, ...

mixture
of two or more
liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers to a fluid flow, flow in which the material density is constant within a fluid par ...

liquid
s that are normally
immiscible Miscibility () is the property of two Chemical substance, substances to mix in all Mixing ratio, proportions (that is, to fully dissolution (chemistry), dissolve in each other at any concentration), forming a Homogeneity and heterogeneity, homogen ...
(unmixable or unblendable) owing to liquid-liquid
phase separation Phase separation is the creation of two distinct phases from a single homogeneous mixture. The most common type of phase separation is between two immiscible liquids such as oil and water. Colloid A colloid is a mixture in which one subs ...

phase separation
. Emulsions are part of a more general class of two-phase systems of
matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic particl ...
called
colloid A colloid is a mixture In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior ...

colloid
s. Although the terms ''colloid'' and ''emulsion'' are sometimes used interchangeably, ''emulsion'' should be used when both phases, dispersed and continuous, are liquids. In an emulsion, one liquid (the dispersed
phase Phase or phases may refer to: Science * State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter) In the physical sciences, a phase is a region of space (a thermodynamic system A thermodynamic system is a ...
) is dispersed in the other (the continuous phase). Examples of emulsions include
vinaigrette Vinaigrette ( ) is made by mixing an oil with something acidic such as vinegar Vinegar is an aqueous solution An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table ...

vinaigrette
s, homogenized
milk Milk is a nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animal Animals (also called Metazoa) are multicellular eukaryotic organisms that ...

milk
, liquid
biomolecular condensate Biomolecular condensates are a class of non-lipid bilayer, membrane bound organelles and organelle subdomains, specified by physical concepts that date back a long way. As with other organelles, biomolecular condensates are specialized subunits of ...
s, and some
cutting fluidImage:Makino-S33-MachiningCenter-example.jpg, Thin-wall milling of aluminum using a water-based cutting fluid on the milling cutter. Cutting fluid is a type of coolant and lubrication, lubricant designed specifically for metalworking processes, such ...
s for
metal working Metalworking is the process of shaping and reshaping metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearan ...

metal working
. Two liquids can form different types of emulsions. As an example, oil and water can form, first, an oil-in-water emulsion, in which the oil is the dispersed phase, and water is the continuous phase. Second, they can form a water-in-oil emulsion, in which water is the dispersed phase and oil is the continuous phase. Multiple emulsions are also possible, including a "water-in-oil-in-water" emulsion and an "oil-in-water-in-oil" emulsion. Emulsions, being liquids, do not exhibit a static internal structure. The droplets dispersed in the continuous phase (sometimes referred to as the "dispersion medium") are usually assumed to be statistically distributed to produce roughly spherical droplets. The term "emulsion" is also used to refer to the photo-sensitive side of
photographic film Photographic film is a strip or sheet of transparent coated on one side with a containing microscopically small light-sensitive crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and of the ...
. Such a
photographic emulsion Photographic emulsion is a light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light is usually defined as having wav ...
consists of
silver halide A silver halide (or silver salt) is one of the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, e ...
colloidal particles dispersed in a
gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen upright=1.5, Tropocollagen molecule: three left-handed procollagens (red, green, blue) j ...
matrix.
Nuclear emulsion In Particle physics, particle and nuclear physics, a nuclear emulsion plate is a photographic plate with a particularly thick emulsion layer and with a very uniform grain size. Like bubble chambers, cloud chambers, and wire chambers nuclear emulsio ...
s are similar to photographic emulsions, except that they are used in particle physics to detect high-energy
elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s (s, s, s, and s), which generally are " particles" and " particles", as well ...
s.


Etymology

The word "emulsion" comes from the Latin ''emulgere'' "to milk out", from ''ex'' "out" + ''mulgere'' "to milk", as milk is an emulsion of fat and water, along with other components, including
colloid A colloid is a mixture In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior ...

colloid
al
casein Casein ( , from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman ...

casein
micelles (a type of secreted
biomolecular condensate Biomolecular condensates are a class of non-lipid bilayer, membrane bound organelles and organelle subdomains, specified by physical concepts that date back a long way. As with other organelles, biomolecular condensates are specialized subunits of ...
).


Appearance and properties

Emulsions contain both a dispersed and a continuous phase, with the boundary between the phases called the "interface". Emulsions tend to have a cloudy appearance because the many phase interfaces
scatter
scatter
light as it passes through the emulsion. Emulsions appear
white White is the lightest color and is achromatic (having no hue). It is the color of snow, chalk, and milk, and is the opposite of black. White objects fully diffuse reflection, reflect and scattering, scatter all the visible spectrum, visible wa ...

white
when all light is scattered equally. If the emulsion is dilute enough, higher-frequency (low-wavelength) light will be scattered more, and the emulsion will appear
blue Blue is one of the three of pigments in painting and traditional , as well as in the . It lies between and on the of . The eye perceives blue when observing light with a between approximately 450 and 495 s. Most blues contain a slight mix ...

blue
r – this is called the "
Tyndall effect
Tyndall effect
". If the emulsion is concentrated enough, the color will be distorted toward comparatively longer wavelengths, and will appear more
yellow Yellow is the color between green and Orange (colour), orange on the Visible spectrum, spectrum of visible light. It is evoked by light with a dominant wavelength of roughly 575585 Nanometre, nm. It is a primary color in subtractive color syst ...

yellow
. This phenomenon is easily observable when comparing
skimmed milk Skimmed milk (British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of grammar and usag ...

skimmed milk
, which contains little fat, to
cream Cream is a dairy product Dairy products or milk products are a type of food Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ' ...

cream
, which contains a much higher concentration of milk fat. One example would be a mixture of water and oil. Two special classes of emulsions –
microemulsionMicroemulsions are clear, thermodynamically stable isotropic Isotropy is uniformity in all orientations; it is derived from the Greek ''isos'' (ἴσος, "equal") and ''tropos'' (τρόπος, "way"). Precise definitions depend on the subject area. ...
s and nanoemulsions, with droplet sizes below 100 nm – appear translucent. This property is due to the fact that light waves are scattered by the droplets only if their sizes exceed about one-quarter of the wavelength of the incident light. Since the
visible spectrum The visible spectrum is the portion of the that is to the . in this range of s is called ' or simply . A typical will respond to wavelengths from about 380 to about 750 . In terms of frequency, this corresponds to a band in the vicinity of ...
of light is composed of wavelengths between 390 and 750
nanometer one nanometric Scanning_Tunneling_Microscope.html"_;"title="carbon_nano_tube,_photographed_with_Scanning_Tunneling_Microscope">carbon_nano_tube,_photographed_with_Scanning_Tunneling_Microscope_ file:EM_Spectrum_Properties_edit.svg.html" ;"title= ...
s (nm), if the droplet sizes in the emulsion are below about 100 nm, the light can penetrate through the emulsion without being scattered. Due to their similarity in appearance, translucent nanoemulsions and microemulsions are frequently confused. Unlike translucent nanoemulsions, which require specialized equipment to be produced, microemulsions are spontaneously formed by "solubilizing" oil molecules with a mixture of
surfactant Surfactants are compounds that lower the surface tension Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension is what allows heavier than water i.e., denser than water objects ...

surfactant
s, co-surfactants, and co-
solvent A solvent (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

solvent
s. The required surfactant concentration in a
microemulsionMicroemulsions are clear, thermodynamically stable isotropic Isotropy is uniformity in all orientations; it is derived from the Greek ''isos'' (ἴσος, "equal") and ''tropos'' (τρόπος, "way"). Precise definitions depend on the subject area. ...
is, however, several times higher than that in a translucent nanoemulsion, and significantly exceeds the concentration of the dispersed phase. Because of many undesirable side-effects caused by surfactants, their presence is disadvantageous or prohibitive in many applications. In addition, the stability of a microemulsion is often easily compromised by dilution, by heating, or by changing pH levels. Common emulsions are inherently unstable and, thus, do not tend to form spontaneously. Energy input – through shaking, stirring, homogenizing, or exposure to power
ultrasound Ultrasound is s with higher than the upper audible limit of human . Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is appro ...

ultrasound
 – 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 ( ) is made by mixing an oil with something acidic such as vinegar Vinegar is an aqueous solution An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table ...
, an unstable emulsion that will quickly separate unless shaken almost continuously. There are important exceptions to this rule – microemulsions are stable, while translucent nanoemulsions are kinetically stable. Whether an emulsion of oil and water turns into a "water-in-oil" emulsion or an "oil-in-water" emulsion depends on the volume fraction of both phases and the type of emulsifier (surfactant) (see ''Emulsifier'', below) present.


Instability

Emulsion stability refers to the ability of an emulsion to resist change in its properties over time. There are four types of instability in emulsions:
flocculation Flocculation, in the field of chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavi ...

flocculation
, coalescence, creaming/
sedimentation Sedimentation is the deposition of sediments Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring solid mass or aggreg ...
, and
Ostwald ripening File:A-general-patterning-approach-by-manipulating-the-evolution-of-two-dimensional-liquid-foams-ncomms14110-s2.ogv, Growth of bubbles in a liquid foam via Ostwald ripening. Ostwald ripening is a phenomenon observed in solid solutions or sol (col ...
. Flocculation occurs when there is an attractive force between the droplets, so they form flocs, like bunches of grapes. This process can be desired, if controlled in its extent, to tune physical properties of emulsions such as their flow behaviour. Coalescence occurs when droplets bump into each other and combine to form a larger droplet, so the average droplet size increases over time. Emulsions can also undergo creaming, where the droplets rise to the top of the emulsion under the influence of
buoyancy Buoyancy (), or upthrust, is an upward exerted by a that opposes the of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bo ...

buoyancy
, or under the influence of the
centripetal force A centripetal force (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power ...

centripetal force
induced when a
centrifuge A centrifuge is a device that uses centrifugal force to separate various components of a fluid. This is achieved by rotation around a fixed axis, spinning the fluid at high speed within a container, thereby separating fluids of different densitie ...

centrifuge
is used. Creaming is a common phenomenon in dairy and non-dairy beverages (i.e. milk, coffee milk, almond milk, soy milk) and usually does not change the droplet size. Sedimentation is the opposite phenomenon of creaming and normally observed in water-in-oil emulsions. Sedimentation happens when the dispersed phase is denser than the continuous phase and the gravitational forces pull the denser globules towards the bottom of the emulsion. Similar to creaming, sedimentation follows Stokes' law. An appropriate "surface active agent" (or "
surfactant Surfactants are compounds that lower the surface tension Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension is what allows heavier than water i.e., denser than water objects ...

surfactant
") can increase the kinetic stability of an emulsion so that the size of the droplets does not change significantly with time. The stability of an emulsion, like a
suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspended ...
, can be studied in terms of
zeta potential Zeta potential is the electrical potential at the slipping plane. This plane is the interface which separates mobile fluid from fluid that remains attached to the surface. Zeta potential is a scientific term for electrokinetic potential in coll ...

zeta potential
, which indicates the repulsion between droplets or particles. If the size and dispersion of droplets does not change over time, it is said to be stable. For example, oil-in-water emulsions containing mono- and diglycerides and milk protein as
surfactant Surfactants are compounds that lower the surface tension Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension is what allows heavier than water i.e., denser than water objects ...

surfactant
showed that stable oil droplet size over 28 days storage at 25°C.


Monitoring physical stability

The stability of emulsions can be characterized using techniques such as light scattering, focused beam reflectance measurement, centrifugation, and
rheology Rheology (; from Ancient Greek, Greek , 'flow' and , , 'study of') is the study of the flow of matter, primarily in a liquid or gas state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than def ...

rheology
. Each method has advantages and disadvantages.


Accelerating methods for shelf life prediction

The kinetic process of destabilization can be rather long – up to several months, or even years for some products. Often the formulator must accelerate this process in order to test products in a reasonable time during product design. Thermal methods are the most commonly used – these consist of increasing the emulsion temperature to accelerate destabilization (if below critical temperatures for phase inversion or chemical degradation). Temperature affects not only the viscosity but also the interfacial tension in the case of non-ionic surfactants or, on a broader scope, interactions between droplets within the system. Storing an emulsion at high temperatures enables the simulation of realistic conditions for a product (e.g., a tube of sunscreen emulsion in a car in the summer heat), but also accelerates destabilization processes up to 200 times. Mechanical methods of acceleration, including vibration, centrifugation, and agitation, can also be used. These methods are almost always empirical, without a sound scientific basis.


Emulsifiers

An emulsifier (also known as an "emulgent") is a substance that stabilizes an emulsion by increasing its
kinetic stability In physics, metastability is a stable state of a dynamical system other than the system's ground state, state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is only slightly pushed, it wil ...
. Emulsifiers are part of a broader group of compounds known as
surfactant Surfactants are compounds that lower the surface tension Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension is what allows heavier than water i.e., denser than water objects ...

surfactant
s, or "surface active agents". Surfactants (emulsifiers) are compounds that are typically
amphiphilic 250px, Cross-section view of the structures that can be formed by phospholipids, biological amphiphiles in aqueous solutions. Unlike this illustration, micelles are usually formed by non-biological, single-chain, amphiphiles, soaps or detergents, ...
, meaning they have a polar or
hydrophilic A hydrophile is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atoms ...

hydrophilic
(i.e. water-soluble) part and a non-polar (i.e. hydrophobic or
lipophilicLipophilicity (from Greek language, Greek λίπος "fat" and :wikt:φίλος, φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar ...
) part. Because of this, emulsifiers tend to have more or less solubility either in water or in oil. Emulsifiers that are more soluble in water (and conversely, less soluble in oil) will generally form oil-in-water emulsions, while emulsifiers that are more soluble in oil will form water-in-oil emulsions. Examples of food emulsifiers are: *
Egg yolk Diagram of a chicken egg in its 9th day. Membranes: allantois, chorion, amnion, and vitellus/ yolk. An egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal ha ...

Egg yolk
 – in which the main emulsifying and thickening agent is
lecithin 300px, An example of a phosphatidylcholine, a type of phospholipid in lecithin. Shown in – choline and phosphate group; – glycerol; – monounsaturated fatty acid; – saturated fatty acid. Lecithin (, from the Greek ''lekithos'' "yolk") ...
. In fact, ''lecithos'' is the Greek word for egg yolk. *
Mustard Mustard may refer to: Food and plants * Mustard (condiment) Mustard is a condiment made from the seeds A seed is an Plant embryogenesis, embryonic plant enclosed in a testa (botany), protective outer covering. The formation of the seed is ...
 – where a variety of chemicals in the
mucilage Mucilage is a thick, gluey substance produced by nearly all plant Plants are mainly multicellular organisms, predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert ...
surrounding the seed hull act as emulsifiers *
Soy lecithin Image:1-Oleoyl-2-almitoyl-phosphatidylcholine Structural Formulae V.1.png, 300px, An example of a phosphatidylcholine, a type of phospholipid in lecithin. Shown in – choline and phosphate group; – glycerol; – monounsaturated fatty acid; ...
is another emulsifier and thickener * Pickering stabilization – uses particles under certain circumstances *
Sodium phosphates Sodium phosphate is a generic term for a variety of salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallin ...
– not directly an emulsifier, but modifies behavior of other molecules, e.g.
casein Casein ( , from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman ...

casein
* Mono- and diglycerides – a common emulsifier found in many food products (coffee creamers, ice-creams, spreads, breads, cakes) * *
DATEM DATEM (diacetyl tartaric acid ester of mono- and diglycerides, also E472e) is an emulsifier primarily used in baking to strengthen the gluten network in dough. It is added to crusty breads, such as rye bread, rye, to impart a springy, chewy textu ...

DATEM
(diacetyl tartaric acid esters of mono- and diglycerides) – an emulsifier used primarily in baking * Simple cellulose – a particulate emulsifier derived from plant material using only water *
Proteins Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a Nobe ...

Proteins
– those with both hydrophilic and hydrophobic regions, e.g. sodium , as in meltable cheese product
Detergent A detergent is a surfactant Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting ...
s are another class of surfactant, and will interact physically with both
oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can b ...
and
water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known forms of , even though it provide ...

water
, thus stabilizing the interface between the oil and water droplets in suspension. This principle is exploited in
soap Soap is a of a used in a variety of cleansing and lubricating products. In a domestic setting, soaps are s usually used for , , and other types of . In industrial settings, soaps are used as s, components of some s, and precursors to s. Wh ...

soap
, to remove grease for the purpose of cleaning agent, cleaning. Many different emulsifiers are used in pharmacy to prepare emulsions such as cream (pharmaceutical), creams and lotions. Common examples include emulsifying wax, polysorbate 20, and ceteareth, ceteareth 20. Sometimes the inner phase itself can act as an emulsifier, and the result is a nanoemulsion, where the inner state disperses into "nano-size" droplets within the outer phase. A well-known example of this phenomenon, the "ouzo effect", happens when water is poured into a strong alcoholic anise-based beverage, such as ouzo, pastis, absinthe, Arak (distilled beverage), arak, or Rakı, raki. The anisolic compounds, which are soluble in ethanol, then form nano-size droplets and emulsify within the water. The resulting color of the drink is opaque and milky white.


Mechanisms of emulsification

A number of different chemical and physical processes and mechanisms can be involved in the process of emulsification: * Surface tension theory – according to this theory, emulsification takes place by reduction of interfacial tension between two phases * Repulsion theory – the emulsifying agent creates a film over one phase that forms globules, which repel each other. This repulsive force causes them to remain suspended in the dispersion medium * Viscosity modification – emulgents like Gum arabic, acacia and tragacanth, which are hydrocolloids, as well as PEG (or polyethylene glycol), glycerine, and other polymers like CMC (carboxymethyl cellulose), all increase the viscosity of the medium, which helps create and maintain the suspension of globules of dispersed phase


Uses


In food

Oil-in-water emulsions are common in food products: * Crema (foam) in espresso – coffee oil in water (brewed coffee), unstable colloid * Mayonnaise and Hollandaise sauces – these are oil-in-water emulsions stabilized with egg yolk
lecithin 300px, An example of a phosphatidylcholine, a type of phospholipid in lecithin. Shown in – choline and phosphate group; – glycerol; – monounsaturated fatty acid; – saturated fatty acid. Lecithin (, from the Greek ''lekithos'' "yolk") ...
, or with other types of food additives, such as sodium stearoyl lactylate * Homogenized milk – an emulsion of milk fat in water, with milk proteins as the emulsifier * Vinaigrette – an emulsion of vegetable oil in vinegar, if this is prepared using only oil and vinegar (i.e., without an emulsifier), an unstable emulsion results Water-in-oil emulsions are less common in food, but still exist: * Butter – an emulsion of water in butterfat * Margarine Other foods can be turned into products similar to emulsions, for example meat emulsion is a suspension of meat in liquid that is similar to true emulsions.


In health care

In pharmaceutics, Hairstyling product, hairstyling, personal hygiene, and cosmetics, emulsions are frequently used. These are usually oil and water emulsions but dispersed, and which is continuous depends in many cases on the pharmaceutical formulation. These emulsions may be called cream (pharmaceutical), creams, ointments, liniments (balms), paste (rheology), pastes, Thin film, films, or
liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers to a fluid flow, flow in which the material density is constant within a fluid par ...

liquid
s, depending mostly on their oil-to-water ratios, other additives, and their intended route of administration. The first 5 are topical dosage forms, and may be used on the surface of the human skin, skin, transdermally, Eye drop, ophthalmically, rectally, or vaginally. A highly liquid emulsion may also be used oral administration, orally, or may be Injection (medicine), injected in some cases. Microemulsions are used to deliver vaccines and kill microbes. Typical emulsions used in these techniques are nanoemulsions of soybean oil, with particles that are 400–600 nm in diameter. The process is not chemical, as with other types of antimicrobial treatments, but mechanical. The smaller the droplet the greater the surface tension and thus the greater the force required to merge with other lipids. The oil is emulsified with detergents using a high-shear mixer to stabilize the emulsion so, when they encounter the lipids in the cell membrane or envelope of Cell envelope, bacteria or viruses, they force the lipids to merge with themselves. On a mass scale, in effect this disintegrates the membrane and kills the pathogen. The soybean oil emulsion does not harm normal human cells, or the cells of most other higher organisms, with the exceptions of Spermatozoon, sperm cells and blood cells, which are vulnerable to nanoemulsions due to the peculiarities of their membrane structures. For this reason, these nanoemulsions are not currently used intravenously (IV). 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 tuberculosis pathogens on non-porous surfaces.


In firefighting

Emulsifying agents are effective at extinguishing fires on small, thin-layer spills of flammable liquids (Fire classes, class B fires). 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 solution, aqueous surfactant solution to the fuel through a high-pressure nozzle. Emulsifiers are not effective at extinguishing large fires involving bulk/deep liquid fuels, because the amount of emulsifier agent needed for extinguishment is a function of the volume of the fuel, whereas other agents such as Fire-fighting foam, aqueous film-forming foam need cover only the surface of the fuel to achieve vapor mitigation.


Chemical synthesis

Emulsions are used to manufacture polymer dispersions – polymer production in an emulsion 'phase' has a number of process advantages, including prevention of coagulation of product. Products produced by such polymerisations may be used as the emulsions – products including primary components for glues and paints. Synthetic latexes (rubbers) are also produced by this process.


See also

* Emulsion dispersion * Emulsified fuel * Homogenizer * Liquid whistle * Miniemulsion * Pickering emulsion * Rheology * Water-in-water emulsion


References


Other sources

* * ''Handbook of Nanostructured Materials and Nanotechnology; Nalwa, H.S., Ed.; Academic Press: New York, NY, USA, 2000; Volume 5, pp. 501–575'' {{Authority control Chemical mixtures Colloidal chemistry Colloids Condensed matter physics Dosage forms Drug delivery devices Soft matter