Emulsion and Colloid

7/30/2019 Emulsion and Colloid

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Emulsion

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A. Two immiscible liquids, not yet emulsifiedB. An emulsion of Phase II dispersed in Phase I

C. The unstable emulsion progressively separates

D. The surfactant (purple 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 normallyimmiscible

(nonmixable or unblendable). Emulsions are part of a more general class of two-phase

systems ofmattercalled colloids. Although the terms colloidand emulsion are sometimesused interchangeably, emulsion should be used when both the dispersed and the

continuous phase are liquids. In an emulsion, one liquid (the dispersedphase) is dispersedin the other (the continuous phase). Examples of emulsions includevinaigrettes,milk,

mayonnaise, and some cutting fluids formetal working. The photo-sensitive side ofphotographic filmis also an example of a colloid.

The word "emulsion" comes from the Latin word for "to milk", as milk is (among other

things) an emulsion of milk fat and water.

Two liquids can form different types of emulsions. As an example, oil and water canform, firstly, an oil-in-water emulsion, where the oil is the dispersed phase, and water is

the dispersion medium. Secondly, they can form a water-in-oil emulsion, where water is

the dispersed phase and oil is the external phase. Multiple emulsions are also possible,including a "water-in-oil-in-water" emulsion and an "oil-in-water-in-oil" emulsion.

Contents

[hide]

1 Structure and properties of emulsions

2 Appearance and properties

o 2.1 Instability

o 2.2 Monitoring physical stability

o 2.3 Accelerating methods for shelf life prediction 3 Emulsifiers

4 Mechanisms of emulsification

5 Uses

o 5.1 In food

o 5.2 In medicine

o 5.3 In firefighting

6 See also
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7 External links

8 References

[edit] Structure and properties of emulsions

Emulsions, being liquids, do not exhibit a static internal structure. The droplets dispersedin the liquid matrix (called the dispersion medium) are usually assumed to be

statistically distributed.

[edit] Appearance and properties

Emulsions contain both a dispersed and a continuous phase, with the boundary betweenthe phases called the "interface". Emulsions tend to have a cloudy appearance because the

manyphase interfacesscatterlight as it passes through the emulsion. Emulsions appear

white when all light is scattered equally. If the emulsion is dilute enough, higher-frequency and low-wavelength light will be scattered more, and the emulsion will appear

bluer- this is called the "Tyndall effect". 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, whichcontains little fat, to cream, which contains a much higher concentration of milk fat.

Two special classes of emulsions - microemulsions and nanoemulsions, with droplet sizes

below 100 nm - appear translucent.[1] This property is due to the fact that light waves arescattered 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 belowabout 100 nm, the light can penetrate through the emulsion without being scattered.[2]

Due to their similarity in appearance, translucent nanoemulsions andmicroemulsionsare

frequently confused. Unlike translucent nanoemulsions, which require specialized

equipment to be produced,[3]microemulsions are spontaneously formed by solubilizingoil molecules with a mixture ofsurfactants, co-surfactants, and co-solvents.[1] The

required surfactant concentration in a microemulsionis, however, several times higher

than that in a translucent nanoemulsion, and significantly exceeds the concentration ofthe 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[4] - is needed to form an emulsion. Over time, emulsions tend to revert to thestable state of the phases comprising the emulsion. An example of this is seen in the

separation of the oil and vinegar components ofvinaigrette, an unstable emulsion that

will quickly separate unless shaken almost continuously. There are important exceptions
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to this rule - microemulsions are thermodynamically stable, while translucent

nanoemulsions are kineticallystable.[1]

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) (seeEmulsifier, below) present. In general, theBancroft ruleapplies.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).

[edit] Instability

Emulsion stability refers to the ability of an emulsion to resist change in its properties

over time.[5] There are three types of instability in emulsions: flocculation,creaming, andcoalescence. Flocculation describes the process by which the dispersed phase comes out

of suspension in the form of flakes. Coalescence is another form of instability - smalldroplets bump into each other within the media volume and continuously combine toform progressively larger droplets. Emulsions can also undergocreaming, where one of

the substances migrates to the top (or the bottom, depending on the relative densities of

the two phases) of the emulsion under the influence ofbuoyancy, or under the influenceof the centripetal force induced when a centrifuge is used.

"Surface active substances" (or "surfactants") can increase the kinetic stability of

emulsions so that the emulsion does not change significantly with 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.

[edit] Monitoring physical stability

Multiple light scattering, coupled with vertical scanning, is the most widely used

technique to monitor the dispersion state of a product that exists as an emulsion. This

technique allows the identification and quantification of destabilizing phenomena.[6][7][8][9]

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 (i.e. creaming) and global changes in size (i.e. flocculation,

coalescence) can be detected and monitored.

[edit] 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. It is often required that the formulator use methods that further

accelerate this process in order to reach a reasonable development time for new productdesigns. Thermal methods are the most commonly used - these consist of increasing the
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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 of forces inside 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 to accelerate destabilization processes up to 200 times.

Mechanical methods of acceleration - including vibration, centrifugation, and agitation -are sometimes used. These subject the product to different forces that push the droplets

against one another. However, some emulsions would never coalesce under normal

gravitational force, but will under highergforces.[10]Moreover, segregation of differentpopulations of particles have also been seen when using centrifugation and vibration

methods.[11]

[edit] Emulsifiers

An emulsifier (also known as an "emulgent") is a substance that stabilizes an emulsion byincreasing its kinetic stability. One class of emulsifiers is known as "surface active

substances", orsurfactants.

Examples of food emulsifiers are:

Egg yolk- in which the main emulsifying agent is lecithin

mustard - where a variety of chemicals in themucilage surrounding the seed hullact as emulsifiers

Proteins Low molecular weight emulsifiers

Soy lecithin is another emulsifier and thickener Pickering stabilization - uses particles under certain circumstances

sodium stearoyl lactylate

DATEM (Diacetyl Tartaric (Acid) Ester of Monoglyceride) - an emulsifierprimarily used in baking

Detergents are another class of surfactants, and will physically interact 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 ofcleaning. Many

different emulsifiers are used inpharmacy to prepare emulsions such as creams andlotions. Common examples include emulsifying wax,cetearyl alcohol,polysorbate 20,

andceteareth 20.[12]Sometimes the inner phase itself can act as an emulsifier, and theresult 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,arak, orraki. The anisolic compounds, which are soluble inethanol, then form nano-size
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droplets and emulsify within the water. The resulting color of the drink is opaque and

milky white.

[edit] Mechanisms of emulsification

A number of different chemical and physical processes and mechanisms can be involvedin 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 formsglobules, which repel each other. This repulsive force causes them to remain

suspended in the dispersion medium

Viscosity modification - emulgents like acacia and tragacanth, which are

hydrocolloids, as well as PEG (or polyethylene glycol), glycerine, and otherpolymers like CMC (carboxymethylcellulose), all increase the viscosity of the

medium, which helps create and maintain the suspension of globules of dispersed

phase

[edit] Uses

[edit] In food

Oil-in-water emulsions are common in food:

Crema in espresso coffee oil in water (brewed coffee), unstable emulsion

Mayonnaise and Hollandaise sauce - these are oil-in-water emulsions that are

stabilized with egg yolklecithin, or with other types of food additives, such assodium stearoyl lactylate

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

Homogenized milk an emulsion of milk fat in water and milk proteins

[edit] In medicine
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20 ml ampule of 1% Propofol emulsion suitable forintravenousinjection. The

manufacturers emulsify lipid-soluble Propofol in a mixture of water, soy oil, and egglecithin.

Inpharmaceutics,hairstyling,personal hygiene, and cosmetics, emulsions are frequentlyused. These are usually oil and water emulsions, but which is dispersed and which is

continuous depends in many cases on thepharmaceutical formulation. These emulsionsmay be called creams, ointments, liniments (balms),pastes,films, orliquids, depending

mostly on their oil-to-water ratios, other additives, and their intendedroute of

administration.[13][14] The first 5 are topicaldosage forms, and may be used on the surfaceof the skin, transdermally, ophthalmically, rectally, orvaginally. A highly liquid

emulsion may also be used orally, or may be injectedin some cases.[13] Popular

medications occurring in emulsion form include calamine lotion,cod liver oil,Polysporin, cortisol cream, Canesten, and Fleet.

Microemulsions are used to delivervaccines and kill microbes.[15] Typical emulsions usedin these techniques are nanoemulsions ofsoybean oil, with particles that are 400-600 nm

in diameter.[16] The process is not chemical, as with other types ofantimicrobialtreatments, but mechanical. The smaller the droplet, the greater the surface tension, and

thus the greater the force required to merge with otherlipids. The oil is emulsified with

detergents using a high-shear mixerto stabilize the emulsion, so when they encounter thelipids in the cell membrane or envelope ofbacteria orviruses, they force the lipids to

merge with themselves. On a mass scale, this effectively disintegrates the membrane and
http://en.wikipedia.org/wiki/Propofolhttp://en.wikipedia.org/wiki/Intravenoushttp://en.wikipedia.org/wiki/Intravenoushttp://en.wikipedia.org/wiki/Lecithinhttp://en.wikipedia.org/wiki/Pharmaceuticshttp://en.wikipedia.org/wiki/Pharmaceuticshttp://en.wikipedia.org/wiki/Hairstyling_producthttp://en.wikipedia.org/wiki/Personal_hygienehttp://en.wikipedia.org/wiki/Personal_hygienehttp://en.wikipedia.org/wiki/Cosmeticshttp://en.wikipedia.org/wiki/Pharmaceutical_formulationhttp://en.wikipedia.org/wiki/Cream_(pharmaceutical)http://en.wikipedia.org/wiki/Ointmenthttp://en.wikipedia.org/wiki/Linimenthttp://en.wikipedia.org/wiki/Paste_(rheology)http://en.wikipedia.org/wiki/Thin_filmhttp://en.wikipedia.org/wiki/Thin_filmhttp://en.wikipedia.org/wiki/Thin_filmhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Route_of_administrationhttp://en.wikipedia.org/wiki/Route_of_administrationhttp://en.wikipedia.org/wiki/Route_of_administrationhttp://en.wikipedia.org/wiki/Route_of_administrationhttp://en.wikipedia.org/wiki/Emulsion#cite_note-Aulton-12%23cite_note-Aulton-12http://en.wikipedia.org/wiki/Emulsion#cite_note-Remington-13%23cite_note-Remington-13http://en.wikipedia.org/wiki/Topicalhttp://en.wikipedia.org/wiki/Dosage_formhttp://en.wikipedia.org/wiki/Human_skinhttp://en.wikipedia.org/wiki/Transdermalhttp://en.wikipedia.org/wiki/Eye_drophttp://en.wikipedia.org/wiki/Rectalhttp://en.wikipedia.org/wiki/Vaginahttp://en.wikipedia.org/wiki/Vaginahttp://en.wikipedia.org/wiki/Oral_administrationhttp://en.wikipedia.org/wiki/Oral_administrationhttp://en.wikipedia.org/wiki/Injection_(medicine)http://en.wikipedia.org/wiki/Injection_(medicine)http://en.wikipedia.org/wiki/Emulsion#cite_note-Aulton-12%23cite_note-Aulton-12http://en.wikipedia.org/wiki/Calamine_lotionhttp://en.wikipedia.org/wiki/Calamine_lotionhttp://en.wikipedia.org/wiki/Cod_liver_oilhttp://en.wikipedia.org/wiki/Cod_liver_oilhttp://en.wikipedia.org/wiki/Polysporinhttp://en.wikipedia.org/wiki/Cortisolhttp://en.wikipedia.org/wiki/Canestenhttp://en.wikipedia.org/wiki/Canestenhttp://en.wikipedia.org/wiki/Fleet_(laxative)http://en.wikipedia.org/wiki/Vaccinehttp://en.wikipedia.org/wiki/Microbehttp://en.wikipedia.org/wiki/Emulsion#cite_note-14%23cite_note-14http://en.wikipedia.org/wiki/Soybean_oilhttp://en.wikipedia.org/wiki/Emulsion#cite_note-15%23cite_note-15http://en.wikipedia.org/wiki/Antimicrobialhttp://en.wikipedia.org/wiki/Antimicrobialhttp://en.wikipedia.org/wiki/Surface_tensionhttp://en.wikipedia.org/wiki/Lipidshttp://en.wikipedia.org/wiki/Lipidshttp://en.wikipedia.org/wiki/Lipidshttp://en.wikipedia.org/wiki/High-shear_mixerhttp://en.wikipedia.org/wiki/High-shear_mixerhttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Cell_envelopehttp://en.wikipedia.org/wiki/Virushttp://en.wikipedia.org/wiki/File:Propofol.jpghttp://en.wikipedia.org/wiki/Propofolhttp://en.wikipedia.org/wiki/Intravenoushttp://en.wikipedia.org/wiki/Lecithinhttp://en.wikipedia.org/wiki/Pharmaceuticshttp://en.wikipedia.org/wiki/Hairstyling_producthttp://en.wikipedia.org/wiki/Personal_hygienehttp://en.wikipedia.org/wiki/Cosmeticshttp://en.wikipedia.org/wiki/Pharmaceutical_formulationhttp://en.wikipedia.org/wiki/Cream_(pharmaceutical)http://en.wikipedia.org/wiki/Ointmenthttp://en.wikipedia.org/wiki/Linimenthttp://en.wikipedia.org/wiki/Paste_(rheology)http://en.wikipedia.org/wiki/Thin_filmhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Route_of_administrationhttp://en.wikipedia.org/wiki/Route_of_administrationhttp://en.wikipedia.org/wiki/Emulsion#cite_note-Aulton-12%23cite_note-Aulton-12http://en.wikipedia.org/wiki/Emulsion#cite_note-Remington-13%23cite_note-Remington-13http://en.wikipedia.org/wiki/Topicalhttp://en.wikipedia.org/wiki/Dosage_formhttp://en.wikipedia.org/wiki/Human_skinhttp://en.wikipedia.org/wiki/Transdermalhttp://en.wikipedia.org/wiki/Eye_drophttp://en.wikipedia.org/wiki/Rectalhttp://en.wikipedia.org/wiki/Vaginahttp://en.wikipedia.org/wiki/Oral_administrationhttp://en.wikipedia.org/wiki/Injection_(medicine)http://en.wikipedia.org/wiki/Emulsion#cite_note-Aulton-12%23cite_note-Aulton-12http://en.wikipedia.org/wiki/Calamine_lotionhttp://en.wikipedia.org/wiki/Cod_liver_oilhttp://en.wikipedia.org/wiki/Polysporinhttp://en.wikipedia.org/wiki/Cortisolhttp://en.wikipedia.org/wiki/Canestenhttp://en.wikipedia.org/wiki/Fleet_(laxative)http://en.wikipedia.org/wiki/Vaccinehttp://en.wikipedia.org/wiki/Microbehttp://en.wikipedia.org/wiki/Emulsion#cite_note-14%23cite_note-14http://en.wikipedia.org/wiki/Soybean_oilhttp://en.wikipedia.org/wiki/Emulsion#cite_note-15%23cite_note-15http://en.wikipedia.org/wiki/Antimicrobialhttp://en.wikipedia.org/wiki/Surface_tensionhttp://en.wikipedia.org/wiki/Lipidshttp://en.wikipedia.org/wiki/High-shear_mixerhttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Cell_envelopehttp://en.wikipedia.org/wiki/Virus


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kills the pathogen. The soybean oil emulsion does not harm normal human cells, or the

cells of most otherhigher organisms, with the exceptions ofsperm cells andblood cells,

which are vulnerable to nanoemulsions due to the peculiarities of their membranestructures. 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 destroyHIV-1andtuberculosis pathogens on non-porous surfaces.

[edit] 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 isachieved by applying an aqueoussurfactant 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 agent needed for extinguishment is a function of the

volume of the fuel, whereas agents such as aqueous film-forming foam (AFFF) needcover only the surface of the fuel to achieve vapor mitigation.[citation needed]

[edit] See also

Colloid

From Wikipedia, the free encyclopedia

Jump to: navigation,search
http://en.wikipedia.org/wiki/Higher_organismshttp://en.wikipedia.org/wiki/Spermatozoonhttp://en.wikipedia.org/wiki/Blood_cellshttp://en.wikipedia.org/wiki/Blood_cellshttp://en.wikipedia.org/wiki/Intravenoushttp://en.wikipedia.org/wiki/Intravenoushttp://en.wikipedia.org/wiki/Disinfectionhttp://en.wikipedia.org/wiki/Surfacehttp://en.wikipedia.org/wiki/Surfacehttp://en.wikipedia.org/wiki/HIV-1http://en.wikipedia.org/wiki/HIV-1http://en.wikipedia.org/wiki/Tuberculosishttp://en.wikipedia.org/wiki/Tuberculosishttp://en.wikipedia.org/wiki/Poroushttp://en.wikipedia.org/w/index.php?title=Emulsion&action=edit&section=11http://en.wikipedia.org/wiki/Fire_classeshttp://en.wikipedia.org/wiki/Aqueous_solutionhttp://en.wikipedia.org/wiki/Aqueous_solutionhttp://en.wikipedia.org/wiki/Fire-fighting_foamhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Emulsion&action=edit&section=12http://en.wikipedia.org/wiki/Colloid#mw-head%23mw-headhttp://en.wikipedia.org/wiki/Colloid#mw-head%23mw-headhttp://en.wikipedia.org/wiki/Colloid#p-search%23p-searchhttp://en.wikipedia.org/wiki/File:Glass_of_milk_on_tablecloth.jpghttp://en.wikipedia.org/wiki/Higher_organismshttp://en.wikipedia.org/wiki/Spermatozoonhttp://en.wikipedia.org/wiki/Blood_cellshttp://en.wikipedia.org/wiki/Intravenoushttp://en.wikipedia.org/wiki/Disinfectionhttp://en.wikipedia.org/wiki/Surfacehttp://en.wikipedia.org/wiki/HIV-1http://en.wikipedia.org/wiki/Tuberculosishttp://en.wikipedia.org/wiki/Poroushttp://en.wikipedia.org/w/index.php?title=Emulsion&action=edit&section=11http://en.wikipedia.org/wiki/Fire_classeshttp://en.wikipedia.org/wiki/Aqueous_solutionhttp://en.wikipedia.org/wiki/Fire-fighting_foamhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Emulsion&action=edit&section=12http://en.wikipedia.org/wiki/Colloid#mw-head%23mw-headhttp://en.wikipedia.org/wiki/Colloid#p-search%23p-search


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Milkis an emulsified colloid of liquidbutterfat globules dispersed within a water-based

solution.

A colloid is a substance microscopically dispersed evenly throughout another substance.[1]

A colloidal system consists of two separate phases: a dispersed phase (orinternal phase)

and a continuous phase (ordispersion medium) in which the colloid is dispersed. A

colloidal system may be solid, liquid, orgas.

The dispersed-phase particles have a diameter of between approximately 1 and 1000nanometers.[2] Such particles are normally invisible in an optical microscope, though their

presence can be confirmed with the use of anultramicroscope or an electron microscope.

Homogeneousmixtures with a dispersed phase in this size range may be called colloidalaerosols, colloidal emulsions, colloidal foams, colloidal dispersions, orhydrosols. The

dispersed-phase particles or droplets are affected largely by the surface chemistry present

in the colloid.

Some colloids are translucent because of the Tyndall effect, which is the scattering oflight by particles in the colloid. Other colloids may be opaque or have a slight color.

Colloidal solutions (also called colloidal suspensions) are the subject ofinterface and

colloid science. This field of study was introduced in 1861 by Scottish scientist Thomas

Graham.

Contents

[hide]

1 Classification

2 Hydrocolloids

3 Interaction between colloid particles

4 Preparation of colloids

5 Stabilization of a colloidal dispersion (peptization)

6 Destabilizing a colloidal dispersion (flocculation)

o 6.1 Technique monitoring colloidal stability

o 6.2 Accelerating methods for shelf life prediction

7 Colloids as a model system for atoms

8 Colloidal crystals 9 Colloids in biology

10 Colloids in the environment

11 Use in intravenous therapy

12 See also

13 References

14 Further reading
http://en.wikipedia.org/wiki/Milkhttp://en.wikipedia.org/wiki/Emulsionhttp://en.wikipedia.org/wiki/Butterfathttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Colloid#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Colloid#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Microscopehttp://en.wikipedia.org/wiki/Ultramicroscopehttp://en.wikipedia.org/wiki/Ultramicroscopehttp://en.wikipedia.org/wiki/Electron_microscopehttp://en.wikipedia.org/wiki/Homogeneous_(chemistry)http://en.wikipedia.org/wiki/Homogeneous_(chemistry)http://en.wikipedia.org/wiki/Surface_sciencehttp://en.wikipedia.org/wiki/Tyndall_effecthttp://en.wikipedia.org/wiki/Interface_and_colloid_sciencehttp://en.wikipedia.org/wiki/Interface_and_colloid_sciencehttp://en.wikipedia.org/wiki/Interface_and_colloid_sciencehttp://en.wikipedia.org/wiki/Scotlandhttp://en.wikipedia.org/wiki/Thomas_Graham_(chemist)http://en.wikipedia.org/wiki/Thomas_Graham_(chemist)http://en.wikipedia.org/wiki/Colloidhttp://en.wikipedia.org/wiki/Colloid#Classification%23Classificationhttp://en.wikipedia.org/wiki/Colloid#Hydrocolloids%23Hydrocolloidshttp://en.wikipedia.org/wiki/Colloid#Interaction_between_colloid_particles%23Interaction_between_colloid_particleshttp://en.wikipedia.org/wiki/Colloid#Preparation_of_colloids%23Preparation_of_colloidshttp://en.wikipedia.org/wiki/Colloid#Stabilization_of_a_colloidal_dispersion_.28peptization.29%23Stabilization_of_a_colloidal_dispersion_.28peptization.29http://en.wikipedia.org/wiki/Colloid#Destabilizing_a_colloidal_dispersion_.28flocculation.29%23Destabilizing_a_colloidal_dispersion_.28flocculation.29http://en.wikipedia.org/wiki/Colloid#Technique_monitoring_colloidal_stability%23Technique_monitoring_colloidal_stabilityhttp://en.wikipedia.org/wiki/Colloid#Accelerating_methods_for_shelf_life_prediction%23Accelerating_methods_for_shelf_life_predictionhttp://en.wikipedia.org/wiki/Colloid#Colloids_as_a_model_system_for_atoms%23Colloids_as_a_model_system_for_atomshttp://en.wikipedia.org/wiki/Colloid#Colloidal_crystals%23Colloidal_crystalshttp://en.wikipedia.org/wiki/Colloid#Colloids_in_biology%23Colloids_in_biologyhttp://en.wikipedia.org/wiki/Colloid#Colloids_in_the_environment%23Colloids_in_the_environmenthttp://en.wikipedia.org/wiki/Colloid#Use_in_intravenous_therapy%23Use_in_intravenous_therapyhttp://en.wikipedia.org/wiki/Colloid#See_also%23See_alsohttp://en.wikipedia.org/wiki/Colloid#References%23Referenceshttp://en.wikipedia.org/wiki/Colloid#Further_reading%23Further_readinghttp://en.wikipedia.org/wiki/Milkhttp://en.wikipedia.org/wiki/Emulsionhttp://en.wikipedia.org/wiki/Butterfathttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Colloid#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Colloid#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Microscopehttp://en.wikipedia.org/wiki/Ultramicroscopehttp://en.wikipedia.org/wiki/Electron_microscopehttp://en.wikipedia.org/wiki/Homogeneous_(chemistry)http://en.wikipedia.org/wiki/Surface_sciencehttp://en.wikipedia.org/wiki/Tyndall_effecthttp://en.wikipedia.org/wiki/Interface_and_colloid_sciencehttp://en.wikipedia.org/wiki/Interface_and_colloid_sciencehttp://en.wikipedia.org/wiki/Scotlandhttp://en.wikipedia.org/wiki/Thomas_Graham_(chemist)http://en.wikipedia.org/wiki/Thomas_Graham_(chemist)http://en.wikipedia.org/wiki/Colloidhttp://en.wikipedia.org/wiki/Colloid#Classification%23Classificationhttp://en.wikipedia.org/wiki/Colloid#Hydrocolloids%23Hydrocolloidshttp://en.wikipedia.org/wiki/Colloid#Interaction_between_colloid_particles%23Interaction_between_colloid_particleshttp://en.wikipedia.org/wiki/Colloid#Preparation_of_colloids%23Preparation_of_colloidshttp://en.wikipedia.org/wiki/Colloid#Stabilization_of_a_colloidal_dispersion_.28peptization.29%23Stabilization_of_a_colloidal_dispersion_.28peptization.29http://en.wikipedia.org/wiki/Colloid#Destabilizing_a_colloidal_dispersion_.28flocculation.29%23Destabilizing_a_colloidal_dispersion_.28flocculation.29http://en.wikipedia.org/wiki/Colloid#Technique_monitoring_colloidal_stability%23Technique_monitoring_colloidal_stabilityhttp://en.wikipedia.org/wiki/Colloid#Accelerating_methods_for_shelf_life_prediction%23Accelerating_methods_for_shelf_life_predictionhttp://en.wikipedia.org/wiki/Colloid#Colloids_as_a_model_system_for_atoms%23Colloids_as_a_model_system_for_atomshttp://en.wikipedia.org/wiki/Colloid#Colloidal_crystals%23Colloidal_crystalshttp://en.wikipedia.org/wiki/Colloid#Colloids_in_biology%23Colloids_in_biologyhttp://en.wikipedia.org/wiki/Colloid#Colloids_in_the_environment%23Colloids_in_the_environmenthttp://en.wikipedia.org/wiki/Colloid#Use_in_intravenous_therapy%23Use_in_intravenous_therapyhttp://en.wikipedia.org/wiki/Colloid#See_also%23See_alsohttp://en.wikipedia.org/wiki/Colloid#References%23Referenceshttp://en.wikipedia.org/wiki/Colloid#Further_reading%23Further_reading


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15 External links

[edit] Classification

Because the size of the dispersed phase may be difficult to measure, and because colloids

have the appearance ofsolutions, colloids are sometimes identified and characterized bytheir physico-chemical and transport properties. For example, if a colloid consists of a

solid phase dispersed in a liquid, the solid particles will not diffuse through a membrane,

whereas with a true solution the dissolved ions or molecules will diffuse through amembrane. Because of the size exclusion, the colloidal particles are unable to pass

through the pores of an ultrafiltration membrane with a size smaller than their own

dimension. The smaller the size of the pore of the ultrafiltration membrane, the lower the

concentration of the dispersed colloidal particules remaining in the ultrafiltred liquid. Theexact value of the concentration of a truly dissolved species will thus depend on the

experimental conditions applied to separate it from the colloidal particles also dispersed

in the liquid. This is, a.o., particularly important forsolubility studies of readilyhydrolysed species such as Al, Eu, Am, Cm, ... ororganic mattercomplexing these

species. Colloids can be classified as follows:

Medium / PhasesDispersed phase

Gas Liquid Solid

Continuousmedium

GasNONE

(All gases are

mutuallymiscible)

Liquid aerosol

Examples: fog,mist,

hair sprays

Solid aerosol

Examples: smoke,

cloud, air particulates

Liquid

Foam

Example: whippedcream, Shaving

cream

Emulsion

Examples:milk,mayonnaise, hand

cream

Sol

Examples:pigmentedink,blood

SolidSolid foam

Examples:aerogel,

styrofoam,pumice

Gel

Examples: agar,

gelatin,jelly, opal

Solid sol

Example:cranberry

glass

In some cases, a colloid can be considered as a homogeneous mixture. This is because thedistinction between "dissolved" and "particulate" matter can be sometimes a matter of

approach, which affects whether or not it is homogeneous or heterogeneous.

[edit] Hydrocolloids

A hydrocolloid is defined as a colloid system wherein the colloid particles arehydrophilic polymers dispersed in water. A hydrocolloid has colloid particles spread

throughout water, and depending on the quantity of water available that can take place in

different states, e.g., gel orsol (liquid). Hydrocolloids can be eitherirreversible (single-state) orreversible. For example,agar, a reversible hydrocolloid ofseaweed extract, can
http://en.wikipedia.org/wiki/Colloid#External_links%23External_linkshttp://en.wikipedia.org/w/index.php?title=Colloid&action=edit&section=1http://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Molecular_diffusionhttp://en.wikipedia.org/wiki/Solubilityhttp://en.wikipedia.org/wiki/Solubilityhttp://en.wikipedia.org/wiki/Hydrolysedhttp://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Complexationhttp://en.wikipedia.org/wiki/Miscibilityhttp://en.wikipedia.org/wiki/Miscibilityhttp://en.wikipedia.org/wiki/Aerosolhttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Misthttp://en.wikipedia.org/wiki/Hair_sprayhttp://en.wikipedia.org/wiki/Smokehttp://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Particulatehttp://en.wikipedia.org/wiki/Foamhttp://en.wikipedia.org/wiki/Whipped_creamhttp://en.wikipedia.org/wiki/Whipped_creamhttp://en.wikipedia.org/wiki/Shaving_creamhttp://en.wikipedia.org/wiki/Shaving_creamhttp://en.wikipedia.org/wiki/Emulsionhttp://en.wikipedia.org/wiki/Milkhttp://en.wikipedia.org/wiki/Milkhttp://en.wikipedia.org/wiki/Mayonnaisehttp://en.wikipedia.org/wiki/Soaphttp://en.wikipedia.org/wiki/Soaphttp://en.wikipedia.org/wiki/Sol_(colloid)http://en.wikipedia.org/wiki/Inkhttp://en.wikipedia.org/wiki/Inkhttp://en.wikipedia.org/wiki/Inkhttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Aerogelhttp://en.wikipedia.org/wiki/Aerogelhttp://en.wikipedia.org/wiki/Styrofoamhttp://en.wikipedia.org/wiki/Pumicehttp://en.wikipedia.org/wiki/Pumicehttp://en.wikipedia.org/wiki/Gelhttp://en.wikipedia.org/wiki/Agarhttp://en.wikipedia.org/wiki/Gelatinhttp://en.wikipedia.org/wiki/Fruit_preserveshttp://en.wikipedia.org/wiki/Fruit_preserveshttp://en.wikipedia.org/wiki/Opalhttp://en.wikipedia.org/wiki/Cranberry_glasshttp://en.wikipedia.org/wiki/Cranberry_glasshttp://en.wikipedia.org/wiki/Cranberry_glasshttp://en.wikipedia.org/w/index.php?title=Colloid&action=edit&section=2http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Gelhttp://en.wikipedia.org/wiki/Sol_(colloid)http://en.wikipedia.org/wiki/Irreversibilityhttp://en.wikipedia.org/wiki/Reversible_reactionhttp://en.wikipedia.org/wiki/Reversible_reactionhttp://en.wikipedia.org/wiki/Agarhttp://en.wikipedia.org/wiki/Agarhttp://en.wikipedia.org/wiki/Agarhttp://en.wikipedia.org/wiki/Seaweedhttp://en.wikipedia.org/wiki/Colloid#External_links%23External_linkshttp://en.wikipedia.org/w/index.php?title=Colloid&action=edit&section=1http://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Molecular_diffusionhttp://en.wikipedia.org/wiki/Solubilityhttp://en.wikipedia.org/wiki/Hydrolysedhttp://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Complexationhttp://en.wikipedia.org/wiki/Miscibilityhttp://en.wikipedia.org/wiki/Aerosolhttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Misthttp://en.wikipedia.org/wiki/Hair_sprayhttp://en.wikipedia.org/wiki/Smokehttp://en.wikipedia.org/wiki/Cloudhttp://en.wikipedia.org/wiki/Particulatehttp://en.wikipedia.org/wiki/Foamhttp://en.wikipedia.org/wiki/Whipped_creamhttp://en.wikipedia.org/wiki/Whipped_creamhttp://en.wikipedia.org/wiki/Shaving_creamhttp://en.wikipedia.org/wiki/Shaving_creamhttp://en.wikipedia.org/wiki/Emulsionhttp://en.wikipedia.org/wiki/Milkhttp://en.wikipedia.org/wiki/Mayonnaisehttp://en.wikipedia.org/wiki/Soaphttp://en.wikipedia.org/wiki/Soaphttp://en.wikipedia.org/wiki/Sol_(colloid)http://en.wikipedia.org/wiki/Inkhttp://en.wikipedia.org/wiki/Inkhttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Aerogelhttp://en.wikipedia.org/wiki/Styrofoamhttp://en.wikipedia.org/wiki/Pumicehttp://en.wikipedia.org/wiki/Gelhttp://en.wikipedia.org/wiki/Agarhttp://en.wikipedia.org/wiki/Gelatinhttp://en.wikipedia.org/wiki/Fruit_preserveshttp://en.wikipedia.org/wiki/Opalhttp://en.wikipedia.org/wiki/Cranberry_glasshttp://en.wikipedia.org/wiki/Cranberry_glasshttp://en.wikipedia.org/w/index.php?title=Colloid&action=edit&section=2http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Gelhttp://en.wikipedia.org/wiki/Sol_(colloid)http://en.wikipedia.org/wiki/Irreversibilityhttp://en.wikipedia.org/wiki/Reversible_reactionhttp://en.wikipedia.org/wiki/Agarhttp://en.wikipedia.org/wiki/Seaweed


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exist in a gel and sol state, and alternate between states with the addition or elimination of

heat.

Many hydrocolloids are derived from natural sources. For example,agar-agarandcarrageenan are extracted from seaweed,gelatinis produced by hydrolysis of proteins of

bovine and fish origins, andpectin is extracted from citrus peel and applepomace.

Gelatin dessertslike jelly orJell-O are made from gelatin powder, another effective

hydrocolloid. Hydrocolloids are employed in food mainly to influencetexture orviscosity (e.g., a sauce). Hydrocolloid-based medical dressings are used forskin and

wound treatment.

Other main hydrocolloids are xanthan gum,gum arabic, guar gum,locust bean gum,

cellulose derivatives as carboxymethyl cellulose, alginate and starch.

[edit] Interaction between colloid particles

The following forces play an important role in the interaction of colloid particles:

Excluded volume repulsion: This refers to the impossibility of any overlap

between hard particles.

Electrostatic interaction: Colloidal particles often carry an electrical charge and

therefore attract or repel each other. The charge of both the continuous and the

dispersed phase, as well as the mobility of the phases are factors affecting this

interaction.

van der Waals forces: This is due to interaction between two dipoles that are

either permanent or induced. Even if the particles do not have a permanent dipole,

fluctuations of the electron density gives rise to a temporary dipole in a particle.This temporary dipole induces a dipole in particles nearby. The temporary dipole

and the induced dipoles are then attracted to each other. This is known as van der

Waals force, and is always present (unless the refractive indexes of the dispersedand continuous phases are matched), is short-range, and is attractive.

Entropic forces: According to the second law of thermodynamics, a system

progresses to a state in which entropy is maximized. This can result in effective

forces even between hard spheres.

Steric forcesbetween polymer-covered surfaces or in solutions containing non-

adsorbing polymer can modulate interparticle forces, producing an additional

steric repulsive force (which is predominantly entropic in origin) or an attractive

depletion force between them. Such an effect is specifically searched for withtailor-made superplasticizersdeveloped to increase the workability of concrete

and to reduce its water content.

[edit] Preparation of colloids

There are two principal ways of preparation of colloids: [3]
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Dispersion of large particles or droplets to the colloidal dimensions by milling,

spraying, or application of shear (e.g., shaking, mixing, orhigh shear mixing).

Condensation of small dissolved molecules into larger colloidal particles byprecipitation, condensation, or redox reactions. Such processes are used in the

preparation of colloidal silica orgold.

[edit] Stabilization of a colloidal dispersion (peptization)

The stability of a colloidal system is the capability of the system to remain as it is.Stability is hindered by aggregation and by sedimentation phenomena, that determine

phase separation.

Examples of a stable and of an unstable colloidal dispersion.

Aggregation is due to the sum of the interaction forces between particles.[4][5] If attractiveforces (such as van der Waals forces) prevail over the repulsive ones (such as the

electrostatic ones) particles aggregate in clusters.

Electrostatic stabilization and steric stabilization are the two main mechanisms forstabilization against aggregation.

Electrostatic stabilization is based on the mutual repulsion of like electrical

charges. In general, different phases have different charge affinities, so that an

electrical double layer forms at any interface. Small particle sizes lead toenormous surface areas, and this effect is greatly amplified in colloids. In a stable

colloid, mass of a dispersed phase is so low that its buoyancy or kinetic energy is

too weak to overcome the electrostatic repulsion between charged layers of thedispersing phase.

Steric stabilization consists in covering the particles in polymers which prevents

the particle to get close in the range of attractive forces.

A combination of the two mechanisms is also possible (electrosteric stabilization). All theabove mentioned mechanisms for minimizing particle aggregation rely on the

enhancement of the repulsive interaction forces.

Electrostatic and steric stabilization do not directly address the sedimentation/floatingproblem.

Particle sedimentation (and also floating, although this phenomenon is less common)

arises from a difference in the density of the dispersed and of the continuous phase. Thehigher the difference in densities, the faster the particle settling.

The gel network stabilization represents the principal way to produce colloids

stable to both aggregation and sedimentation.[6][7]
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The method consists in adding to the colloidal suspension a green biopolymer able to

form a gel network and characterized by shear thinning properties. Examples of such

substances are xanthan and guar gum.

Steric and Gel network stabilization.

Particle settling is hindered by the stiffness of the polymeric matrix where particles are

trapped.[6] In addition, the long polymeric chains can provide a steric or electrosteric

stabilization to dispersed particles.The rheological shear thinning properties find beneficial in the preparation of the

suspensions and in their use, as the reduced viscosity at high shear rates facilitates

deagglomeration, mixing and in general the flow of the suspensions.

[edit] Destabilizing a colloidal dispersion (flocculation)

Unstable colloidal dispersions form flocsas the particles aggregate due to interparticle

attractions. In this way photonic glasses can be grown. This can be accomplished by a

number of different methods:

Removal of the electrostatic barrier that prevents aggregation of the particles. This

can be accomplished by the addition of salt to a suspension or changing the pH of

a suspension to effectively neutralize or "screen" the surface charge of the

particles in suspension. This removes the repulsive forces that keep colloidalparticles separate and allows for coagulation due to van der Waals forces.

Addition of a charged polymer flocculant. Polymer flocculants can bridge

individual colloidal particles by attractive electrostatic interactions. For example,negatively-charged colloidal silica or clay particles can be flocculated by the

addition of a positively-charged polymer.

Addition of non-adsorbed polymers called depletants that cause aggregation dueto entropic effects.

Physical deformation of the particle (e.g., stretching) may increase the van der

Waals forces more than stabilization forces (such as electrostatic), resulting

coagulation of colloids at certain orientations.

Unstable colloidal suspensions of low-volume fraction form clustered liquid suspensions,

wherein individual clusters of particles fall to the bottom of the suspension (or float to the

top if the particles are less dense than the suspending medium) once the clusters are ofsufficient size for the Brownian forcesthat work to keep the particles in suspension to be

overcome by gravitational forces. However, colloidal suspensions of higher-volume

fraction form colloidal gels with viscoelastic properties. Viscoelastic colloidal gels, such

asbentonite and toothpaste, flow like liquids under shear, but maintain their shape whenshear is removed. It is for this reason that toothpaste can be squeezed from a toothpaste

tube, but stays on the toothbrush after it is applied.
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[edit] Technique monitoring colloidal stability

Measurement principle of multiple light scattering coupled with vertical scanning

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.[8][9][10][11] It works on concentrated dispersions without dilution.When light is sent through the sample, it is backscattered by the particles / droplets. The

backscattering intensity is directly proportional to the size and volume fraction of the

dispersed phase. Therefore, local changes in concentration (e.g.Creamingand

Sedimentation) and global changes in size (e.g.flocculation, coalescence) are detected

and monitored.

[edit] Accelerating methods for shelf life prediction

The kinetic process of destabilisation can be rather long (up to several months or evenyears 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 and consists in increasingtemperature 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 more generally interactions forces inside

the system. Storing a dispersion at high temperatures enables to simulate real lifeconditions 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 includingvibration,centrifugation and agitation are sometimes used. They subject the product to

different forces that pushes the particles / droplets against one another, hence helping in

the film drainage. However, some emulsions would never coalesce in normal gravity,

while they do under artificial gravity.[12] Moreover segregation of different populations ofparticles have been highlighted when using centrifugation and vibration.[13]
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[edit] Colloids as a model system for atoms

Inphysics, colloids are an interesting model system foratoms. Micrometre-scale

colloidal particles are large enough to be observed by optical techniques such asconfocalmicroscopy. Many of the forces that govern the structure and behavior of matter, such as

excluded volume interactions or electrostatic forces, govern the structure and behavior ofcolloidal suspensions. For example, the same techniques used to model ideal gases can beapplied to model the behavior of a hard sphere colloidal suspension. In addition, phase

transitions in colloidal suspensions can be studied in real time using optical techniques,

and are analogous to phase transitions in liquids.

[edit] Colloidal crystals

Main article: Colloidal crystal

A colloidal crystal is a highly orderedarray of particles that can be formed over a verylong range (typically on the order of a few millimeters to one centimeter) and that appear

analogous to their atomic or molecular counterparts.[14] One of the finest natural examplesof this ordering phenomenon can be found in precious opal, in which brilliant regions of

pure spectralcolorresult from close-packed domains ofamorphous colloidal spheres of

silicon dioxide (orsilica, SiO2).[15][16] These spherical particlesprecipitate in highly

siliceous pools inAustralia and elsewhere, and form these highly ordered arrays after

years ofsedimentation and compression underhydrostaticand gravitational forces. The

periodic arrays of submicrometre spherical particles provide similar arrays ofinterstitialvoids, which act as a natural diffraction grating forvisiblelightwaves, particularly when

the interstitial spacing is of the same order of magnitudeas the incident lightwave.[17][18]

Thus, it has been known for many years that, due torepulsiveCoulombic interactions,

electrically chargedmacromolecules in anaqueous environment can exhibit long-rangecrystal-like correlations with interparticle separation distances, often being considerably

greater than the individual particle diameter. In all of these cases in nature, the same

brilliant iridescence (or play of colors) can be attributed to the diffraction and

constructive interference of visible lightwaves that satisfy Braggs law, in a matteranalogous to the scatteringofX-rays in crystalline solids.

The large number of experiments exploring thephysics and chemistryof these so-called

"colloidal crystals" has emerged as a result of the relatively simple methods that have

evolved in the last 20 years for preparing synthetic monodisperse colloids (both polymerand mineral) and, through various mechanisms, implementing and preserving their long-

range order formation.

[edit] Colloids in biology

In the early 20th century, beforeenzymology was well understood, colloids were thought

to be the key to the operation ofenzymes; i.e., the addition of small quantities of an
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enzyme to a quantity of water would, in some fashion yet to be specified, subtly alter the

properties of the water so that it would break down the enzyme's specific substrate,[citation

needed] such as a solution ofATPase breaking down ATP. Furthermore, life itself wasexplainable in terms of the aggregate properties of all the colloidal substances that make

up anorganism. As more detailed knowledge ofbiologyandbiochemistrydeveloped, the

colloidal theory was replaced by themacromoleculartheory, which explains an enzymeas a collection of identical huge molecules that act as very tiny machines, freely moving

about between the water molecules of the solution and individually operating on the

substrate, no more mysterious than a factory full of machinery. The properties of thewater in the solution are not altered, other than the simple osmotic changes that would be

caused by the presence of anysolute. In humans, both thethyroid gland and the

intermediate lobe (pars intermedia) of thepituitary gland contain colloid follicles.

[edit] Colloids in the environment

Colloidal particles can also serve as transport vector[19] of diverse contaminants in the

surface water (sea water, lakes, rivers, fresh water bodies) and in underground watercirculating in fissured rocks[20](limestone, sandstone,granite, ...). Radionuclides and

heavy metals easily sorb onto colloids suspended in water. Various types of colloids arerecognised: inorganic colloids (clay particles, silicates, iron oxy-hydroxides, ...), organic

colloids (humic andfulvic substances). When heavy metals or radionuclides form their

own pure colloids, the term "Eigencolloid" is used to designate pure phases, e.g.,Tc(OH)4, U(OH)4, Am(OH)3. Colloids have been suspected for the long-range transport

of plutonium on theNevada Nuclear Test Site. They have been the subject of detailed

studies for many years. However, the mobility of inorganic colloids is very low incompactedbentonitesand in deep clay formations[21]because of the process of

ultrafiltration occurring in dense clay membrane.[22] The question is less clear for small

organic colloids often mixed in porewater with truly dissolved organic molecules. [23]

[edit] Use in intravenous therapy

Colloid solutions used in intravenous therapy belong to a major group ofvolume

expanders, and can be used for intravenous fluid replacement. Colloids preserve a high

colloid osmotic pressurein the blood,[24]and therefore, they should theoreticallypreferentially increase theintravascular volume, whereas other types of volume

expanders called crystalloids also increases theinterstitial volumeandintracellular

volume. However, there is still controversy to the actual difference in efficacy by this

difference.[24]Another difference is that crystalloids generally are much cheaper thancolloids.[24] Recently, however, it has been determined that the use of colloids was

bolstered by faked research studies.[25][clarification needed]
http://en.wikipedia.org/wiki/Enzyme_substratehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/ATPasehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Lifehttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Biochemistryhttp://en.wikipedia.org/wiki/Biochemistryhttp://en.wikipedia.org/wiki/Biochemistryhttp://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Machinehttp://en.wikipedia.org/wiki/Machinehttp://en.wikipedia.org/wiki/Factoryhttp://en.wikipedia.org/wiki/Osmosishttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Thyroid_glandhttp://en.wikipedia.org/wiki/Thyroid_glandhttp://en.wikipedia.org/wiki/Intermediate_lobehttp://en.wikipedia.org/wiki/Pituitary_glandhttp://en.wikipedia.org/wiki/Pituitary_glandhttp://en.wikipedia.org/w/index.php?title=Colloid&action=edit&section=12http://en.wikipedia.org/wiki/Colloid#cite_note-18%23cite_note-18http://en.wikipedia.org/wiki/Colloid#cite_note-19%23cite_note-19http://en.wikipedia.org/wiki/Colloid#cite_note-19%23cite_note-19http://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Granitehttp://en.wikipedia.org/wiki/Sorptionhttp://en.wikipedia.org/wiki/Clayhttp://en.wikipedia.org/wiki/Ferrihydritehttp://en.wikipedia.org/wiki/Humic_acidhttp://en.wikipedia.org/wiki/Fulvic_acidhttp://en.wikipedia.org/wiki/Fulvic_acidhttp://en.wikipedia.org/wiki/Eigencolloidhttp://en.wikipedia.org/wiki/Nevada_Test_Sitehttp://en.wikipedia.org/wiki/Bentonitehttp://en.wikipedia.org/wiki/Bentonitehttp://en.wikipedia.org/wiki/Colloid#cite_note-20%23cite_note-20http://en.wikipedia.org/wiki/Colloid#cite_note-20%23cite_note-20http://en.wikipedia.org/wiki/Ultrafiltrationhttp://en.wikipedia.org/wiki/Colloid#cite_note-21%23cite_note-21http://en.wikipedia.org/wiki/Colloid#cite_note-22%23cite_note-22http://en.wikipedia.org/w/index.php?title=Colloid&action=edit&section=13http://en.wikipedia.org/wiki/Intravenous_therapyhttp://en.wikipedia.org/wiki/Volume_expanderhttp://en.wikipedia.org/wiki/Volume_expanderhttp://en.wikipedia.org/wiki/Fluid_replacementhttp://en.wikipedia.org/wiki/Fluid_replacementhttp://en.wikipedia.org/wiki/Colloid_osmotic_pressurehttp://en.wikipedia.org/wiki/Colloid_osmotic_pressurehttp://en.wikipedia.org/wiki/Colloid#cite_note-gregory-23%23cite_note-gregory-23http://en.wikipedia.org/wiki/Colloid#cite_note-gregory-23%23cite_note-gregory-23http://en.wikipedia.org/wiki/Intravascular_volumehttp://en.wikipedia.org/wiki/Intravascular_volumehttp://en.wikipedia.org/wiki/Crystalloid_solutionhttp://en.wikipedia.org/wiki/Interstitial_volumehttp://en.wikipedia.org/wiki/Interstitial_volumehttp://en.wikipedia.org/wiki/Interstitial_volumehttp://en.wikipedia.org/wiki/Intracellular_volumehttp://en.wikipedia.org/wiki/Intracellular_volumehttp://en.wikipedia.org/wiki/Intracellular_volumehttp://en.wikipedia.org/wiki/Colloid#cite_note-gregory-23%23cite_note-gregory-23http://en.wikipedia.org/wiki/Colloid#cite_note-gregory-23%23cite_note-gregory-23http://en.wikipedia.org/wiki/Colloid#cite_note-gregory-23%23cite_note-gregory-23http://en.wikipedia.org/wiki/Colloid#cite_note-24%23cite_note-24http://en.wikipedia.org/wiki/Colloid#cite_note-24%23cite_note-24http://en.wikipedia.org/wiki/Wikipedia:Please_clarifyhttp://en.wikipedia.org/wiki/Wikipedia:Please_clarifyhttp://en.wikipedia.org/wiki/Enzyme_substratehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/ATPasehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Lifehttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Biochemistryhttp://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Machinehttp://en.wikipedia.org/wiki/Factoryhttp://en.wikipedia.org/wiki/Osmosishttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Thyroid_glandhttp://en.wikipedia.org/wiki/Intermediate_lobehttp://en.wikipedia.org/wiki/Pituitary_glandhttp://en.wikipedia.org/w/index.php?title=Colloid&action=edit&section=12http://en.wikipedia.org/wiki/Colloid#cite_note-18%23cite_note-18http://en.wikipedia.org/wiki/Colloid#cite_note-19%23cite_note-19http://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Granitehttp://en.wikipedia.org/wiki/Sorptionhttp://en.wikipedia.org/wiki/Clayhttp://en.wikipedia.org/wiki/Ferrihydritehttp://en.wikipedia.org/wiki/Humic_acidhttp://en.wikipedia.org/wiki/Fulvic_acidhttp://en.wikipedia.org/wiki/Eigencolloidhttp://en.wikipedia.org/wiki/Nevada_Test_Sitehttp://en.wikipedia.org/wiki/Bentonitehttp://en.wikipedia.org/wiki/Colloid#cite_note-20%23cite_note-20http://en.wikipedia.org/wiki/Ultrafiltrationhttp://en.wikipedia.org/wiki/Colloid#cite_note-21%23cite_note-21http://en.wikipedia.org/wiki/Colloid#cite_note-22%23cite_note-22http://en.wikipedia.org/w/index.php?title=Colloid&action=edit&section=13http://en.wikipedia.org/wiki/Intravenous_therapyhttp://en.wikipedia.org/wiki/Volume_expanderhttp://en.wikipedia.org/wiki/Volume_expanderhttp://en.wikipedia.org/wiki/Fluid_replacementhttp://en.wikipedia.org/wiki/Colloid_osmotic_pressurehttp://en.wikipedia.org/wiki/Colloid#cite_note-gregory-23%23cite_note-gregory-23http://en.wikipedia.org/wiki/Intravascular_volumehttp://en.wikipedia.org/wiki/Crystalloid_solutionhttp://en.wikipedia.org/wiki/Interstitial_volumehttp://en.wikipedia.org/wiki/Intracellular_volumehttp://en.wikipedia.org/wiki/Intracellular_volumehttp://en.wikipedia.org/wiki/Colloid#cite_note-gregory-23%23cite_note-gregory-23http://en.wikipedia.org/wiki/Colloid#cite_note-gregory-23%23cite_note-gregory-23http://en.wikipedia.org/wiki/Colloid#cite_note-24%23cite_note-24http://en.wikipedia.org/wiki/Wikipedia:Please_clarify

Emulsion and Colloid

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