Emulsion

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Two immiscible liquids, not yet emulsifior An emulsion of Phase II dispersed in Phase I The unstable emulsion progressively separates The surfactant (outline around particles) positions itself on the interfaces between Phase II and Phase I, stabilizing the emulsion Emulsions.svg
  1. Two immiscible liquids, not yet emulsifior
  2. An emulsion of Phase II dispersed in Phase I
  3. The unstable emulsion progressively separates
  4. The surfactant (outline around particles) positions itself on the interfaces between Phase II and Phase I, stabilizing the emulsion

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.

Contents

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]

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. 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.

IUPAC definition for an emulsion IUPAC definition for an emulsion.png
IUPAC definition for an emulsion

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

Appearance and properties

Emulsions contain both a dispersed and a continuous phase, with the boundary between the phases called the "interface". [3] Emulsions tend to have a cloudy appearance because the many phase interfaces scatter light as it passes through the emulsion. Emulsions appear white when all light is scattered equally. If the emulsion is dilute enough, higher-frequency (shorter-wavelength) light will be scattered more, and the emulsion will appear bluer  – this is called the "Tyndall effect". [4] If the emulsion is concentrated enough, the color will be distorted toward comparatively longer wavelengths, and will appear more yellow. This phenomenon is easily observable when comparing skimmed milk, which contains little fat, to cream, which contains a much higher concentration of milk fat. One example would be a mixture of water and oil. [5]

Two special classes of emulsions – microemulsions and nanoemulsions, with droplet sizes below 100 nm – appear translucent. [6] 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 of light is composed of wavelengths between 390 and 750 nanometers (nm), if the droplet sizes in the emulsion are below about 100 nm, the light can penetrate through the emulsion without being scattered. [7] 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 surfactants, co-surfactants, and co-solvents. [6] The required surfactant concentration in a microemulsion 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.[ citation needed ]

Common emulsions are inherently unstable and, thus, do not tend to form spontaneously. Energy input – through shaking, stirring, homogenizing, or exposure to power ultrasound [8]  – 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, an unstable emulsion that will quickly separate unless shaken almost continuously. There are important exceptions to this rule – microemulsions are thermodynamically stable, while translucent nanoemulsions are kinetically stable. [6]

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. [9]

Instability

Emulsion stability refers to the ability of an emulsion to resist change in its properties over time. [10] [11] 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. [12] 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. [10] 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. [13] Sedimentation is the opposite phenomenon of creaming and normally observed in water-in-oil emulsions. [3] 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. [14] 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 25 °C. [13]

Monitoring physical stability

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. [15]

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. [16] 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). [17] 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.[ citation needed ]

Mechanical methods of acceleration, including vibration, centrifugation, and agitation, can also be used. [18]

These methods are almost always empirical, without a sound scientific basis.[ citation needed ]

Emulsifiers

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". [19] 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 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. [20]

Examples of food emulsifiers are:

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. [22]

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. [23]

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.

Mechanisms of emulsification

A number of different chemical and physical processes and mechanisms can be involved in the process of emulsification: [3]

Uses

In food

An example of the ingredients used to make mayonnaise; olive oil, table salt, an egg (for yolk) and a lemon (for lemon juice). The oil and water in the egg yolk do not mix, while the lecithin in the yolk serves as an emulsifier, allowing the two to be blended together. Ingredients maonesa.jpg
An example of the ingredients used to make mayonnaise; olive oil, table salt, an egg (for yolk) and a lemon (for lemon juice). The oil and water in the egg yolk do not mix, while the lecithin in the yolk serves as an emulsifier, allowing the two to be blended together.

Oil-in-water emulsions are common in food products:

Water-in-oil emulsions are less common in food, but still exist:

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, 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. [24] [25] 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. [24]

Microemulsions are used to deliver vaccines and kill microbes. [26] Typical emulsions used in these techniques are nanoemulsions of soybean oil, with particles that are 400–600 nm in diameter. [27] 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 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 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.

Applications in Pharmaceutical industry

  • Oral drug delivery: Emulsions may provide an efficient means of administering drugs that are poorly soluble or have low bioavailability or dissolution rates, increasing both dissolution rates and absorption to increase bioavailability and improve bioavailability. By increasing surface area provided by an emulsion, dissolution rates and absorption rates of drugs are increased, improving their bioavailability. [28]
  • Topical formulations: Emulsions are widely utilized as bases for topical drug delivery formulations such as creams, lotions and ointments. Their incorporation allows lipophilic as well as hydrophilic drugs to be mixed together for maximum skin penetration and permeation of active ingredients. [29]
  • Parenteral drug delivery: Emulsions serve as carriers for intravenous or intramuscular administration of drugs, solubilizing lipophilic ones while protecting from degradation and decreasing injection site irritation. Examples include propofol as a widely used anesthetic and lipid-based solutions used for total parenteral nutrition delivery. [30]
  • Ocular Drug Delivery: Emulsions can be used to formulate eye drops and other ocular drug delivery systems, increasing drug retention time in the eye and permeating through corneal barriers more easily while providing sustained release of active ingredients and thus increasing therapeutic efficacy. [31]
  • Nasal and Pulmonary Drug Delivery: Emulsions can be an ideal vehicle for creating nasal sprays and inhalable drug products, enhancing drug absorption through nasal and pulmonary mucosa while providing sustained release with reduced local irritation. [32]
  • Vaccine Adjuvants: Emulsions can serve as vaccine adjuvants by strengthening immune responses against specific antigens. Emulsions can enhance antigen solubility and uptake by immune cells while simultaneously providing controlled release, amplifying an immunological response and thus amplifying its effect. [33]
  • Taste Masking: Emulsions can be used to encase bitter or otherwise unpleasant-tasting drugs, masking their taste and increasing patient compliance - particularly with pediatric formulations. [33]
  • Cosmeceuticals: Emulsions are widely utilized in cosmeceuticals products that combine cosmetic and pharmaceutical properties. These emulsions act as carriers for active ingredients like vitamins, antioxidants and skin lightening agents to provide improved skin penetration and increased stability. [34]

In firefighting

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. [35]

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

Related Research Articles

<span class="mw-page-title-main">Colloid</span> Mixture of an insoluble substance microscopically dispersed throughout another substance

A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend the definition to include substances like aerosols and gels. The term colloidal suspension refers unambiguously to the overall mixture. A colloid has a dispersed phase and a continuous phase. The dispersed phase particles have a diameter of approximately 1 nanometre to 1 micrometre.

<span class="mw-page-title-main">Surfactant</span> Substance that lowers the surface tension between a liquid and another material

Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word "surfactant" is a blend of surface-active agent, coined c. 1950. As they consist of a water-repellent and a water-attracting part, they enable water and oil to mix; they can form foam and facilitate the detachment of dirt.

In polymer chemistry, emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomers, and surfactants. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer are emulsified in a continuous phase of water. Water-soluble polymers, such as certain polyvinyl alcohols or hydroxyethyl celluloses, can also be used to act as emulsifiers/stabilizers. The name "emulsion polymerization" is a misnomer that arises from a historical misconception. Rather than occurring in emulsion droplets, polymerization takes place in the latex/colloid particles that form spontaneously in the first few minutes of the process. These latex particles are typically 100 nm in size, and are made of many individual polymer chains. The particles are prevented from coagulating with each other because each particle is surrounded by the surfactant ('soap'); the charge on the surfactant repels other particles electrostatically. When water-soluble polymers are used as stabilizers instead of soap, the repulsion between particles arises because these water-soluble polymers form a 'hairy layer' around a particle that repels other particles, because pushing particles together would involve compressing these chains.

<span class="mw-page-title-main">Suspension (chemistry)</span> Heterogeneous mixture of solid particles dispersed in a medium

In chemistry, a suspension is a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation. The particles may be visible to the naked eye, usually must be larger than one micrometer, and will eventually settle, although the mixture is only classified as a suspension when and while the particles have not settled out.

<span class="mw-page-title-main">Lecithin</span> Generic term for amphiphilic substances of plant and animal origin

Lecithin is a generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues which are amphiphilic – they attract both water and fatty substances, and are used for smoothing food textures, emulsifying, homogenizing liquid mixtures, and repelling sticking materials.

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(s) and/or other ingredients, and the "oil" may actually be a complex mixture of different hydrocarbons. In contrast to ordinary emulsions, microemulsions form upon simple mixing of the components and do not require the high shear conditions generally used in the formation of ordinary emulsions. The three basic types of microemulsions are direct, reversed and bicontinuous.

<span class="mw-page-title-main">Cream (pharmacy)</span> Preparation for application to the skin or mucous membranes

A cream is a preparation usually for application to the skin. Creams for application to mucous membranes such as those of the rectum or vagina are also used. Creams may be considered pharmaceutical products, since even cosmetic creams are manufactured using techniques developed by pharmacy and unmedicated creams are highly used in a variety of skin conditions (dermatoses). The use of the finger tip unit concept may be helpful in guiding how much topical cream is required to cover different areas.

<span class="mw-page-title-main">Polysorbate 80</span> Nonionic surfactant and emulsifier used in food and cosmetics

Polysorbate 80 is a nonionic surfactant and emulsifier often used in pharmaceuticals, foods, and cosmetics. This synthetic compound is a viscous, water-soluble yellow liquid.

The Bancroft rule in colloidal chemistry states: "The phase in which an emulsifier is more soluble constitutes the continuous phase." This means that water-soluble surfactants tend to give oil-in-water emulsions and oil-soluble surfactants give water-in-oil emulsions. It is a general rule of thumb, still used, but regarded as inferior to HLD theory, which takes many more factors into consideration.

<span class="mw-page-title-main">Miniemulsion</span> Particular type of emulsion

A miniemulsion is a particular type of emulsion. A miniemulsion is obtained by shearing a mixture comprising two immiscible liquid phases, one or more surfactants and, possibly, one or more co-surfactants. They usually have nanodroplets with uniform size distribution (20–500 nm) and are also known as sub-micron, mini-, and ultra-fine grain emulsions.

A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid to improve the separation of the particles and to prevent their settling or clumping.

<span class="mw-page-title-main">Ouzo effect</span> Phenomenon observed in drink mixing

The ouzo effect, also known as the louche effect and spontaneous emulsification, is the phenomenon of formation of a milky oil-in-water emulsion when water is added to ouzo and other anise-flavored liqueurs and spirits, such as pastis, rakı, arak, sambuca and absinthe. Such emulsions occur with only minimal mixing and are highly stable.

A Ramsden emulsion, sometimes named Pickering emulsion, is an emulsion that is stabilized by solid particles which adsorb onto the interface between the water and oil phases. Typically, the emulsions are either water-in-oil or oil-in-water emulsions, but other more complex systems such as water-in-water, oil-in-oil, water-in-oil-in-water, and oil-in-water-in-oil also do exist. Pickering emulsions were named after S.U. Pickering, who described the phenomenon in 1907, although the effect was first recognized by Walter Ramsden in 1903.

<span class="mw-page-title-main">Emulsion dispersion</span> Thermoplastics or elastomers suspended in a liquid state by means of emulsifiers

An emulsion dispersion is thermoplastics or elastomers suspended in a liquid state by means of emulsifiers.

Meat emulsion is a two-phase system, with the dispersed phase consisting of either solid or liquid fat particles and the continuous phase being the water containing salts and dissolved, gelled and suspended proteins. Thus, they can be classified as oil-in-water emulsion. Meat emulsion is not a true emulsion since the two phases involved are not liquids and the fat droplets in a commercial emulsion are larger than 50 μm in diameter and thus do not conform to one of the requirement of a classical emulsion. Common examples of meat emulsions include bologna, frankfurters, sausages, and meatloaf.

<span class="mw-page-title-main">Membrane emulsification</span>

Membrane emulsification (ME) is a relatively novel technique for producing all types of single and multiple emulsions for DDS, solid micro carriers for encapsulation of drug or nutrient, solder particles for surface-mount technology, mono dispersed polymer microspheres. Membrane emulsification was introduced by Nakashima and Shimizu in the late 1980s in Japan.

Paint has four major components: pigments, binders, solvents, and additives. Pigments serve to give paint its color, texture, toughness, as well as determining if a paint is opaque or not. Common white pigments include titanium dioxide and zinc oxide. Binders are the film forming component of a paint as it dries and affects the durability, gloss, and flexibility of the coating. Polyurethanes, polyesters, and acrylics are all examples of common binders. The solvent is the medium in which all other components of the paint are dissolved and evaporates away as the paint dries and cures. The solvent also modifies the curing rate and viscosity of the paint in its liquid state. There are two types of paint: solvent-borne and water-borne paints. Solvent-borne paints use organic solvents as the primary vehicle carrying the solid components in a paint formulation, whereas water-borne paints use water as the continuous medium. The additives that are incorporated into paints are a wide range of things which impart important effects on the properties of the paint and the final coating. Common paint additives are catalysts, thickeners, stabilizers, emulsifiers, texturizers, biocides to fight bacterial growth, etc.

Emulsified Fuels are emulsions composed of water and a combustible liquid, either oil or a fuel. Emulsions are a particular example of a dispersion comprising a continuous and a dispersed phase. The most commonly used emulsion fuel is water-in-diesel emulsion. In the case of emulsions, both phases are the immiscible liquids, oil and water. Emulsion fuels can be either a microemulsion or an ordinary emulsion. The essential differences between the two are stability and particle size distribution. Microemulsions are isotropic whereas macroemulsions are prone to settling and changes in particle size over time. Both use surfactants and can be either water-in-oil, or oil-in-water or bicontinuous.

Macroemulsions are dispersed liquid-liquid, thermodynamically unstable systems with particle sizes ranging from 1 to 100 μm, which, most often, do not form spontaneously. Macroemulsions scatter light effectively and therefore appear milky, because their droplets are greater than a wavelength of light. They are part of a larger family of emulsions along with miniemulsions. As with all emulsions, one phase serves as the dispersing agent. It is often called the continuous or outer phase. The remaining phase(s) are disperse or inner phase(s), because the liquid droplets are finely distributed amongst the larger continuous phase droplets. This type of emulsion is thermodynamically unstable, but can be stabilized for a period of time with applications of kinetic energy. Surfactants are used to reduce the interfacial tension between the two phases, and induce macroemulsion stability for a useful amount of time. Emulsions can be stabilized otherwise with polymers, solid particles or proteins.

<span class="mw-page-title-main">Topical cream formulation</span>

Topical cream formulation is an emulsion semisolid dosage form that is used for skin external application. Most of the topical cream formulations contain more than 20 per cent of water and volatiles and/or less than 50 per cent of hydrocarbons, waxes, or polyethylene glycols as the vehicle for external skin application. In a topical cream formulation, ingredients are dissolved or dispersed in either a water-in-oil (W/O) emulsion or an oil-in-water (O/W) emulsion. The topical cream formulation has a higher content of oily substance than gel, but a lower content of oily ingredient than ointment. Therefore, the viscosity of topical cream formulation lies between gel and ointment. The pharmacological effect of the topical cream formulation is confined to the skin surface or within the skin. Topical cream formulation penetrates through the skin by transcellular route, intercellular route, or trans-appendageal route. Topical cream formulation is used for a wide range of diseases and conditions, including atopic dermatitis (eczema), psoriasis, skin infection, acne, and wart. Excipients found in a topical cream formulation include thickeners, emulsifying agents, preservatives, antioxidants, and buffer agents. Steps required to manufacture a topical cream formulation include excipient dissolution, phase mixing, introduction of active substances, and homogenization of the product mixture.

References

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  23. ↑ Anne-Marie Faiola (2008-05-21). "Using Emulsifying Wax". TeachSoap.com. Retrieved 2008-07-22.
  24. 1 2 Aulton, Michael E., ed. (2007). Aulton's Pharmaceutics: The Design and Manufacture of Medicines (3rd ed.). Churchill Livingstone. pp. 92–97, 384, 390–405, 566–69, 573–74, 589–96, 609–10, 611. ISBN   978-0-443-10108-3.
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  26. ↑ "Adjuvant Vaccine Development". Archived from the original on 2008-07-05. Retrieved 2008-07-23.
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  28. ↑ Sharma, Dr Anubhav (2023-04-26). "Role of Surfactant in Emulsion Stabilization: A Comprehensive Overview". Witfire. Retrieved 2023-04-27.
  29. ↑ Apostolidis, Eftychios; Stoforos, George N.; Mandala, Ioanna (April 2023). "Starch physical treatment, emulsion formation, stability, and their applications". Carbohydrate Polymers. 305: 120554. doi:10.1016/j.carbpol.2023.120554. ISSN   0144-8617. PMID   36737219. S2CID   255739614.
  30. ↑ Hazt, Bianca; Pereira Parchen, Gabriela; Fernanda Martins do Amaral, Lilian; Rondon Gallina, Patrícia; Martin, Sandra; Hess Gonçalves, Odinei; Alves de Freitas, Rilton (April 2023). "Unconventional and conventional Pickering emulsions: Perspectives and challenges in skin applications". International Journal of Pharmaceutics. 636: 122817. doi:10.1016/j.ijpharm.2023.122817. hdl: 10198/16535 . ISSN   0378-5173. PMID   36905974. S2CID   257474428.
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  32. ↑ Udepurkar, Aniket Pradip; Clasen, Christian; Kuhn, Simon (March 2023). "Emulsification mechanism in an ultrasonic microreactor: Influence of surface roughness and ultrasound frequency". Ultrasonics Sonochemistry. 94: 106323. doi:10.1016/j.ultsonch.2023.106323. ISSN   1350-4177. PMC   9945801 . PMID   36774674.
  33. 1 2 Hong, Xin; Zhao, Qiaoli; Liu, Yuanfa; Li, Jinwei (2021-08-13). "Recent advances on food-grade water-in-oil emulsions: Instability mechanism, fabrication, characterization, application, and research trends". Critical Reviews in Food Science and Nutrition. 63 (10): 1406–1436. doi:10.1080/10408398.2021.1964063. ISSN   1040-8398. PMID   34387517. S2CID   236998385.
  34. ↑ Xu, Tian; Jiang, Chengchen; Huang, Zehao; Gu, Zhengbiao; Cheng, Li; Hong, Yan (January 2023). "Formation, stability and the application of Pickering emulsions stabilized with OSA starch/chitosan complexes". Carbohydrate Polymers. 299: 120149. doi:10.1016/j.carbpol.2022.120149. ISSN   0144-8617. PMID   36876777. S2CID   252553332.
  35. ↑ Friedman, Raymond (1998). Principles of Fire Protection Chemistry and Physics. Jones & Bartlett Learning. ISBN   978-0-87765-440-7.

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