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An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion should be used when both phases, dispersed and continuous, are liquids. In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include vinaigrettes, homogenized milk, liquid biomolecular condensates, and some cutting fluids for 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.[1]

The term "emulsion" is also used to refer to the photo-sensitive side of photographic film. Such a photographic emulsion consists of silver halide colloidal particles dispersed in a gelatin matrix. Nuclear emulsions are similar to photographic emulsions, except that they are used in particle physics to detect high-energy elementary particles.

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 colloidal casein micelles (a type of secreted biomolecular condensate).[2]

Note 4: An emulsion is termed an oil/water (o/w) emulsion if thedispersed phase is an organic material and the continuous phase iswater or an aqueous solution and is termed water/oil (w/o) if the dispersedphase is water or an aqueous solution and the continuous phase is anorganic liquid (an "oil").

Note 5: A w/o emulsion is sometimes called an inverse emulsion.The term "inverse emulsion" is misleading, suggesting incorrectly thatthe emulsion has properties that are the opposite of those of an emulsion.Its use is, therefore, not recommended.[4]

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.[11]

Emulsion stability refers to the ability of an emulsion to resist change in its properties over time.[12][13] There are four types of instability in emulsions: flocculation, coalescence, creaming/sedimentation, and Ostwald ripening. 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. [14] 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, or under the influence of the centripetal force induced when a centrifuge is used.[12] 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.[15] Sedimentation is the opposite phenomenon of creaming and normally observed in water-in-oil emulsions.[5] 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) 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, can be studied in terms of 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.[16] For example, oil-in-water emulsions containing mono- and diglycerides and milk protein as surfactant showed that stable oil droplet size over 28 days storage at 25C.[15]

The stability of emulsions can be characterized using techniques such as light scattering, focused beam reflectance measurement, centrifugation, and rheology. Each method has advantages and disadvantages.[17]

An emulsifier is a substance that stabilizes an emulsion by reducing the oil-water interface tension. Emulsifiers are a part of a broader group of compounds known as surfactants, or "surface-active agents".[20] Surfactants are compounds that are typically amphiphilic, meaning they have a polar or hydrophilic (i.e. water-soluble) part and a non-polar (i.e. hydrophobic or lipophilic) part. Emulsifiers[21] 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.[22]

In food emulsions, the type of emulsifier greatly affects how emulsions are structured in the stomach and how accessible the oil is for gastric lipases, thereby influencing how fast emulsions are digested and trigger a satiety inducing hormone response.[25]

Detergents are another class of surfactant, and will interact physically with both oil and water, thus stabilizing the interface between the oil and water droplets in suspension. This principle is exploited in soap, to remove grease for the purpose of cleaning. Many different emulsifiers are used in pharmacy to prepare emulsions such as creams and lotions. Common examples include emulsifying wax, polysorbate 20, and ceteareth 20.[26]

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, or 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.

In pharmaceutics, 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 creams, ointments, liniments (balms), pastes, films, or liquids, depending mostly on their oil-to-water ratios, other additives, and their intended route of administration.[27][28] The first 5 are topical dosage forms, and may be used on the surface of the skin, transdermally, ophthalmically, rectally, or vaginally. A highly liquid emulsion may also be used orally, or may be injected in some cases.[27]

Emulsifying agents are effective at extinguishing fires on small, thin-layer spills of flammable liquids (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 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 aqueous film-forming foam need cover only the surface of the fuel to achieve vapor mitigation.[31]

Works better than anything I have ever used. I have Lupus and periodically get a lupus butterfly rash. This product, the face wash, and 1 a wk mask have made my skin better than it has ever been. At 59, I have attached a photo w/o makeup after using mask & emulsion.

An emulsion is a mixture of two or more liquids that are usually immiscible but under specific transforming processes will adopt a macroscopic homogeneous aspect and a microscopic heterogeneous one. In an emulsion, one liquid is dispersed in the other. There are several types of emulsions:

Although the terms colloid and emulsion are at times used indistinctly, emulsion applies only when both phases, dispersed and continuous, are liquids. A colloid is a mixture of a compound that is in solid, liquid, or gas state and a liquid. The critical difference between colloid and emulsion is that colloid can form when any state of matter (solid, gas, or liquid) combine with a liquid. In contrast, the emulsion has two liquid components that are initially immiscible with each other.

Emulsions, as liquids, do not demonstrate a static internal structure. Emulsions are thermodynamically unstable as both the dispersed and continuous phases can revert as separate phases, oil, and water; by fusion or the coalescing of droplets. Industries use emulsifying agents, e.g., surfactants to maintain a static structure.[1] Usually, the phase in which the surfactant exhibits the greatest solubility becomes the continuous phase. Thus, hydrophilic surfactants foster O/W emulsions, whereas lipophilic surfactants promote W/O emulsions.

Emulsions are frequently used in pharmaceuticals, personal hygiene products, and cosmetics. These are usually oil and water emulsions, albeit dispersed. These emulsions are called creams, ointments, balms, pastes, films, or liquids, depending on their oil-to-water ratios, the addition of other additives, and their intended administration route. Emulsions allow the encapsulation of an active ingredient in the dispersed phase, to protect it from degradation and to preserve its activity in a sustained manner. They are used to make medications more palatable, to improve their effectiveness via dosage control of active ingredients, and to provide better aesthetics for topical drugs such as ointments. Intravenous and parenteral emulsions may be used for nutritive therapy applications when a patient is unable to consume food or receive nutrition. Fat emulsions serve as dietary complements for patients who cannot get the required fat solely from their diet. For oral administration, the compound may be given in the form of a tablet, capsule, granule, or powder. 041b061a72

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