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{{Short description|Mixture of an insoluble substance microscopically dispersed throughout another substance}} | {{Short description|Mixture of an insoluble substance microscopically dispersed throughout another substance}} | ||
{{Use dmy dates|date=March 2021}} | {{Use dmy dates|date=March 2021}} | ||
{{Lead extra info|date=January 2026}} | |||
{{Condensed matter physics}} | {{Condensed matter physics}} | ||
A '''colloid''' is a [[mixture]] in which one substance consisting of microscopically [[Dispersion (chemistry)|dispersed]] [[insoluble]] [[particle]]s is [[suspension (chemistry)|suspended]] throughout another substance. Some definitions specify that the particles must be dispersed in a [[liquid]],<ref name="Israelachvili-2011">{{Cite book |last=Israelachvili |first=Jacob N. |title=Intermolecular and surface forces |date=2011 |publisher=Academic Press |isbn=978-0-08-092363-5|edition=4rd |location=Burlington, MA |oclc=706803091}}</ref> while others extend the definition to include substances like [[aerosol]]s and [[gel]]s. The term '''colloidal suspension''' refers unambiguously to the overall mixture (although a narrower sense of the word ''[[suspension (chemistry)|suspension]]'' is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). | A '''colloid''' is a [[mixture]] in which one substance, consisting of microscopically [[Dispersion (chemistry)|dispersed]] [[insoluble]] [[particle]]s, is [[suspension (chemistry)|suspended]] throughout another substance. Some definitions specify that the particles must be dispersed in a [[liquid]],<ref name="Israelachvili-2011">{{Cite book |last=Israelachvili |first=Jacob N. |title=Intermolecular and surface forces |date=2011 |publisher=Academic Press |isbn=978-0-08-092363-5|edition=4rd |location=Burlington, MA |oclc=706803091}}</ref> while others extend the definition to include substances like [[aerosol]]s and [[gel]]s. The term '''colloidal suspension''' refers unambiguously to the overall mixture (although a narrower sense of the word ''[[suspension (chemistry)|suspension]]'' is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). | ||
[[File:SEM Image of Colloidal Particles.jpg|thumb|upright=1.2|[[Scanning electron microscope]] image of a colloid]] | |||
Some colloids are [[translucent]] because of the [[Tyndall effect]], which is the [[scattering]] of light by particles in the colloid. Other colloids may be [[Opacity (optics)|opaque]] or have a slight color. | |||
Colloidal suspensions are the subject of [[interface and colloid science]]. This field of study began in 1845 with [[Francesco Selmi]],<ref>Selmi, Francesco "Studi sulla dimulsione di cloruro d'argento". ''Nuovi Annali delle Scienze Naturali di Bologna, 1845''.</ref><ref>Selmi, Francesco, Studio intorno alle pseudo-soluzioni degli azzurri di Prussia ed alla influenza dei sali nel guastarle, Bologna: Tipi Sassi, 1847</ref><ref>Hatschek, Emil, The Foundations of Colloid Chemistry, A selection of early papers bearing on the subject, The British Association Committee on Colloid Chemistry, London, 1925</ref><ref>Selmi, Francesco - Sur le soufre pseudosoluble, sa pseudosolution e le soufre mou, Journal de Pharmacie et de Chimie, tome 21, 1852, Paris</ref> who called them pseudosolutions, and was later expanded by [[Michael Faraday]]<ref>Faraday, Michael, ''The Bakerian Lecture, Experimental relations of gold (and other metals) to light'' </ref><ref>{{cite journal|doi=10.1162/posc.2006.14.1.97|title=Discovering Discovery: How Faraday Found the First Metallic Colloid |year=2006 |last1=Tweney |first1=Ryan D. |journal=Perspectives on Science |volume=14 |pages=97–121 |s2cid=55882753 }}</ref> and [[Thomas Graham (chemist)|Thomas Graham]], who coined the term ''colloid'' in 1861.<ref>{{cite journal|doi=10.1098/rstl.1861.0011|title=X. Liquid diffusion applied to analysis |journal=Philosophical Transactions of the Royal Society of London |year=1861 |volume=151 |pages=183–224 |s2cid=186208563 }}. Page 183: "As gelatine appears to be its type, it is proposed to designate substances of the class as ''colloids'', and to speak of their peculiar form of aggregation as the ''colloidal condition of matter''."</ref> | |||
==Definition== | |||
{{Quote box | |||
| title = [[IUPAC]] definition | | title = [[IUPAC]] definition | ||
| width = 35% | | width = 35% | ||
| quote = '''Colloid''': Short synonym for ''colloidal'' system.<ref name=quote1>{{cite book|title=Compendium of Polymer Terminology and Nomenclature (IUPAC Recommendations 2008)|year=2009|publisher=RSC Publ.|isbn=978-0-85404-491-7| | | quote = '''Colloid''': Short synonym for ''colloidal'' system.<ref name=quote1>{{cite book|title=Compendium of Polymer Terminology and Nomenclature (IUPAC Recommendations 2008)|year=2009|publisher=RSC Publ.|isbn=978-0-85404-491-7|page=464|edition= 2nd|editor1=Richard G. Jones |editor2=Edward S. Wilks |editor3=W. Val Metanomski |editor4=Jaroslav Kahovec |editor5=Michael Hess |editor6=Robert Stepto |editor7=Tatsuki Kitayama }}</ref><ref name=quote2>{{cite journal|title=Dispersity in polymer science (IUPAC Recommendations 2009)|journal=[[Pure and Applied Chemistry]]|year=2009|volume=81|issue=2|pages=351–353|doi=10.1351/PAC-REC-08-05-02|url=http://pac.iupac.org/publications/pac/pdf/2009/pdf/8102x0351.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://pac.iupac.org/publications/pac/pdf/2009/pdf/8102x0351.pdf |archive-date=2022-10-09 |url-status=live|last1=Stepto|first1=Robert F. T.|s2cid=95122531}}</ref> | ||
'''Colloidal''': State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm, or that in a system discontinuities are found at distances of that order.<ref name=quote1 /><ref name=quote2 /><ref>{{cite journal|title=Terminology of polymers<br/>and polymerization processes in dispersed systems (IUPAC Recommendations 2011)|journal=[[Pure and Applied Chemistry]]|year=2011|volume=83|issue=12|pages=2229–2259|doi=10.1351/PAC-REC-10-06-03|url=http://pac.iupac.org/publications/pac/pdf/2011/pdf/8312x2229.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://pac.iupac.org/publications/pac/pdf/2011/pdf/8312x2229.pdf |archive-date=2022-10-09 |url-status=live|last1=Slomkowski|first1=Stanislaw|last2=Alemán|first2=José V.|last3=Gilbert|first3=Robert G.|last4=Hess|first4=Michael|last5=Horie|first5=Kazuyuki|last6=Jones|first6=Richard G.|last7=Kubisa|first7=Przemyslaw|last8=Meisel|first8=Ingrid|last9=Mormann|first9=Werner|last10=Penczek|first10=Stanisław|last11=Stepto|first11=Robert F. T.|s2cid=96812603}}</ref> | '''Colloidal''': State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm, or that in a system discontinuities are found at distances of that order.<ref name=quote1 /><ref name=quote2 /><ref>{{cite journal|title=Terminology of polymers<br/>and polymerization processes in dispersed systems (IUPAC Recommendations 2011)|journal=[[Pure and Applied Chemistry]]|year=2011|volume=83|issue=12|pages=2229–2259|doi=10.1351/PAC-REC-10-06-03|url=http://pac.iupac.org/publications/pac/pdf/2011/pdf/8312x2229.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://pac.iupac.org/publications/pac/pdf/2011/pdf/8312x2229.pdf |archive-date=2022-10-09 |url-status=live|last1=Slomkowski|first1=Stanislaw|last2=Alemán|first2=José V.|last3=Gilbert|first3=Robert G.|last4=Hess|first4=Michael|last5=Horie|first5=Kazuyuki|last6=Jones|first6=Richard G.|last7=Kubisa|first7=Przemyslaw|last8=Meisel|first8=Ingrid|last9=Mormann|first9=Werner|last10=Penczek|first10=Stanisław|last11=Stepto|first11=Robert F. T.|s2cid=96812603}}</ref> | ||
}} | }} | ||
Since the definition of a colloid is so ambiguous, the [[International Union of Pure and Applied Chemistry]] (IUPAC) formalized a modern definition of colloids: {{blockquote|The term colloidal refers to a state of subdivision, implying that the molecules or polymolecular particles dispersed in a medium have at least in one direction a dimension roughly between 1 [[nanometre]] and 1 [[micrometre]], or that in a system discontinuities are found at distances of that order. It is not necessary for all three dimensions to be in the colloidal range…Nor is it necessary for the units of a colloidal system to be discrete…The size limits given above are not rigid since they will depend to some extent on the properties under consideration.<ref>{{Cite book|author1=International Union of Pure and Applied Chemistry. Subcommittee on Polymer Terminology|title=Compendium of polymer terminology and nomenclature: IUPAC recommendations, 2008|date=2009|publisher=Royal Society of Chemistry|author2=Jones, Richard G. |isbn=978-1-84755-942-5|location=Cambridge|oclc=406528399}}</ref>}} This IUPAC definition is particularly important because it highlights the flexibility inherent in colloidal systems. However, much of the confusion surrounding colloids arises from oversimplifications. IUPAC makes it clear that exceptions exist, and the definition should not be viewed as a rigid rule. D.H. Everett—the scientist who wrote the IUPAC definition—emphasized that colloids are often better understood through examples rather than strict definitions.<ref>{{Cite book |last=Everett |first=Dogulas H. |title=Basic Principles of Colloid Science |date=1988 |publisher=The Royal Society of Chemistry |isbn=978-0-85186-443-3|location=London}}</ref> | |||
==Classification== | ==Classification== | ||
Colloids can be classified as follows: | Colloids can be classified as follows: | ||
{| class="wikitable" style="text-align:center" | {| class="wikitable" style="text-align:center; max-width:900px" | ||
|- | |- | ||
! colspan="2" rowspan="2" | | ! colspan="2" rowspan="2" | | ||
! colspan="3" | Dispersed phase | ! colspan="3" | Dispersed phase | ||
|- | |- | ||
| Line 30: | Line 34: | ||
! rowspan="3" | Dispersion <br />medium | ! rowspan="3" | Dispersion <br />medium | ||
! Gas | ! Gas | ||
| style="vertical-align: top;" | | style="vertical-align: top;" | '''No such colloids are known''' | ||
|style="vertical-align: top;"|'''Liquid [[aerosol]]''' | ---- | ||
|style="vertical-align: top;"|'''Solid aerosol''' | Helium and xenon are known to be [[immiscible]] under certain conditions.<ref name="de Swaan AronsDiepen2010">{{cite journal|last1=de Swaan Arons|first1=J.|last2=Diepen|first2=G. A. M.|title=Immiscibility of gases. The system He-Xe: (Short communication)|journal=Recueil des Travaux Chimiques des Pays-Bas|volume=82|issue=8|year=2010|page=806|doi=10.1002/recl.19630820810}}</ref><ref name="de Swaan AronsDiepen1996">{{Cite journal|last1=de Swaan Arons|first1=J.|last2=Diepen|first2=G. A. M.|year=1966|title=Gas—Gas Equilibria|journal=J. Chem. Phys.|volume=44|issue=6|page=2322|doi=10.1063/1.1727043|bibcode=1966JChPh..44.2322D}}</ref> | ||
| style="vertical-align: top;"|'''Liquid [[aerosol]]''' | |||
---- | |||
Examples: [[fog]], '''[[cloud]]s''', [[condensation]], [[mist]], [[steam]], [[hair spray]]s[[File:2013-05-19 15-05-07-nuages.jpg|none|120px]] | |||
| style="vertical-align: top;"|'''Solid aerosol''' | |||
---- | |||
Examples: '''[[smoke]]''', [[ice cloud]], [[atmospheric particulate matter]] [[File:Smoke Incense AB.jpg|none|120px]] | |||
|- | |- | ||
! Liquid | ! Liquid | ||
|style="vertical-align: top;"|'''[[Foam]]''' | | style="vertical-align: top;"|'''[[Foam]]''' | ||
|style="vertical-align: top;"|'''[[Emulsion]] or [[Liquid crystal]]''' | ---- | ||
|style="vertical-align: top;"|'''[[Sol (colloid)|Sol]]''' | Examples: '''[[whipped cream]]''', [[shaving cream]][[File:Crème Chantilly.jpg|none|120px]] | ||
| style="vertical-align: top;"|'''[[Emulsion]] or [[Liquid crystal]]''' | |||
---- | |||
Examples: '''[[milk]]''', [[mayonnaise]], [[hand cream]], [[latex]], {{nobr|[[biological membranes]]}}, liquid [[biomolecular condensate]][[File:Glass of Milk (33657535532).jpg|none|120px]] | |||
| style="vertical-align: top;"|'''[[Sol (colloid)|Sol]]''' | |||
---- | |||
Examples: [[ink|pigmented ink]], [[sedimentation|sediment]], '''[[mud]]''', [[precipitates]], solid [[biomolecular condensate]][[File:Bubbling Mud Volcano (3860838997).jpg|none|120px]] | |||
|- | |- | ||
! Solid | ! Solid | ||
|style="vertical-align: top;"|'''Solid foam''' | | style="vertical-align: top;"|'''Solid foam''' | ||
|style="vertical-align: top;"|'''[[Gel]]''' | ---- | ||
|style="vertical-align: top;"|'''Solid sol''' | Examples: '''[[aerogel]]''', [[Ivory (soap)|floating soap]], [[Expanded polystyrene|styrofoam]], [[pumice]][[File:Aerogel hand.jpg|none|120px]] | ||
| style="vertical-align: top;"|'''[[Gel]]''' | |||
---- | |||
Examples: [[agar]], '''[[gelatin]]''', [[Fruit preserves|jelly]], {{nowrap|gel-like [[biomolecular condensate]]}}[[File:Jello Cubes.jpg|none|120px]] | |||
| style="vertical-align: top;"|'''Solid sol''' | |||
---- | |||
Example: '''[[cranberry glass]]'''[[File:Vintage cranberry glass.jpg|none|120px]] | |||
|} | |} | ||
| Line 48: | Line 70: | ||
<gallery mode="packed"> | <gallery mode="packed"> | ||
File:Opaleszens Kolloid SiO2.jpg|Colloidal [[silica gel]] with light [[opalescence]] | File:Opaleszens Kolloid SiO2.jpg|Colloidal [[silica gel]] with light [[opalescence]] | ||
File:Dollop of hair gel.jpg|A dollop of hair gel | File:Dollop of hair gel.jpg|A dollop of hair gel | ||
File:Cream in round container.jpg|[[Cream (pharmacy)|Creams]] are semi-solid emulsions of oil and water. Oil-in-water creams are used for cosmetic purpose while water-in-oil creams for medicinal purpose | File:Cream in round container.jpg|[[Cream (pharmacy)|Creams]] are semi-solid emulsions of oil and water. Oil-in-water creams are used for cosmetic purpose while water-in-oil creams for medicinal purpose | ||
File:Why is the sky blue.jpg|[[Tyndall effect]] in an [[opalite]]:<br>it scatters blue light making it appear blue from the side, but orange light shines through.<br>[[Opal]] is a gel in which water is dispersed in silica [[Colloidal crystal|crystals]]. | File:Why is the sky blue.jpg|[[Tyndall effect]] in an [[opalite]]:<br />it scatters blue light making it appear blue from the side, but orange light shines through.<br />[[Opal]] is a gel in which water is dispersed in silica [[Colloidal crystal|crystals]]. | ||
File:Mist - Ensay region3.jpg|Mist | File:Mist - Ensay region3.jpg|Mist | ||
</gallery> | </gallery> | ||
| Line 66: | Line 84: | ||
===Components=== | ===Components=== | ||
Hydrocolloids contain some type of gel-forming agent, such as sodium carboxymethylcellulose (NaCMC) or gelatin. They are normally combined with some type of sealant, | Hydrocolloids contain some type of gel-forming agent, such as sodium carboxymethylcellulose (NaCMC) or gelatin. They are normally combined with some type of sealant, like polyurethane, to stick to skin. | ||
== Compared with solution == | == Compared with solution == | ||
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== Interaction between particles == | == Interaction between particles == | ||
The following forces play an important role in the interaction of colloid particles:<ref name="Lekkerkerker">{{cite book| last1=Lekkerkerker| first1=Henk N.W.| last2=Tuinier| first2=Remco| title=Colloids and the Depletion Interaction| publisher=Springer| location=Heidelberg| date=2011| doi=10.1007/978-94-007-1223-2| isbn= | The following forces play an important role in the interaction of colloid particles:<ref name="Lekkerkerker">{{cite book| last1=Lekkerkerker| first1=Henk N.W.| last2=Tuinier| first2=Remco| title=Colloids and the Depletion Interaction| publisher=Springer| location=Heidelberg| date=2011| doi=10.1007/978-94-007-1223-2| isbn=978-94-007-1222-5| url=https://cds.cern.ch/record/1399210| access-date=5 September 2018| archive-url=https://web.archive.org/web/20190414163235/https://cds.cern.ch/record/1399210| archive-date=14 April 2019}}</ref><ref name="vanAndersPNAS2014">{{cite journal|last1=van Anders| first1=Greg| last2=Klotsa| first2=Daphne| last3=Ahmed| first3=N. Khalid| last4=Engel| first4=Michael| last5=Glotzer| first5=Sharon C.| date=2014| title=Understanding shape entropy through local dense packing|journal=Proc Natl Acad Sci USA|volume=111| issue=45|pages=E4812–E4821|doi=10.1073/pnas.1418159111|arxiv=1309.1187| pmid=25344532| pmc=4234574|bibcode=2014PNAS..111E4812V| doi-access=free}}</ref> | ||
*[[Excluded volume|Excluded volume repulsion]]: This refers to the impossibility of any overlap between hard particles. | *[[Excluded volume|Excluded volume repulsion]]: This refers to the impossibility of any overlap between hard particles. | ||
*[[Coulomb's law|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. | *[[Coulomb's law|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. | ||
| Line 81: | Line 99: | ||
== Sedimentation velocity == | == Sedimentation velocity == | ||
[[File:Brownian Motion.gif|thumb|Brownian motion of 350 nm diameter polymer colloidal particles.|268x268px]] | [[File:Brownian Motion.gif|thumb|Brownian motion of 350 nm diameter polymer colloidal particles.|268x268px]] | ||
The | The Earth's [[gravitational field]] acts upon colloidal particles. Therefore, if the colloidal particles are denser than the medium of suspension, they will [[Sedimentation|sediment]] (fall to the bottom), or if they are less dense, they will [[Creaming (chemistry)|cream]] (float to the top). Larger particles also have a greater tendency to sediment because they have smaller [[Brownian motion]] to counteract this movement. | ||
The sedimentation or creaming velocity is found by equating the [[Stokes' law|Stokes drag force]] with the [[gravitational force]]: | The sedimentation or creaming velocity is found by equating the [[Stokes' law|Stokes drag force]] with the [[gravitational force]]: | ||
| Line 111: | Line 129: | ||
:<math>v = \frac{m_Ag}{6\pi\eta r}</math> | :<math>v = \frac{m_Ag}{6\pi\eta r}</math> | ||
There is an upper | There is an upper limit on the diameter of colloidal particles, because particles larger than 1 μm tend to sediment; thus, the substance would no longer be considered a colloidal suspension.<ref name="cosgrove2010">{{Cite book|last=Cosgrove|first=Terence|title=Colloid Science: Principles, Methods and Applications|publisher=[[John Wiley & Sons]]|year=2010|isbn=978-1-4443-2018-3}}</ref> | ||
The colloidal particles are said to be in [[sedimentation equilibrium]] if the rate of sedimentation is equal to the rate of movement from Brownian motion. | The colloidal particles are said to be in [[sedimentation equilibrium]], if the rate of sedimentation is equal to the rate of movement from Brownian motion. | ||
==Preparation== | ==Preparation== | ||
| Line 128: | Line 146: | ||
Electrostatic stabilization and steric stabilization are the two main mechanisms for stabilization against aggregation. | Electrostatic stabilization and steric stabilization are the two main mechanisms for stabilization against aggregation. | ||
* Electrostatic stabilization is based on the mutual repulsion of like electrical charges. The charge of colloidal particles is structured in an [[electrical double layer]], where the particles are charged on the surface, but then attract counterions (ions of opposite charge) which surround the particle. The electrostatic repulsion between suspended colloidal particles is most readily quantified in terms of the [[zeta potential]]. The combined effect of van der Waals attraction and electrostatic repulsion on aggregation is described quantitatively by the [[DLVO theory]].<ref>{{Cite journal|date=2011-01-01|title=Intermolecular Force|journal=Interface Science and Technology|volume=18|pages=1–57|doi=10.1016/B978-0-12-375049-5.00001-3|last1=Park|first1=Soo-Jin|last2=Seo|first2=Min-Kang|isbn= | * Electrostatic stabilization is based on the mutual repulsion of like electrical charges. The charge of colloidal particles is structured in an [[electrical double layer]], where the particles are charged on the surface, but then attract counterions (ions of opposite charge) which surround the particle. The electrostatic repulsion between suspended colloidal particles is most readily quantified in terms of the [[zeta potential]]. The combined effect of van der Waals attraction and electrostatic repulsion on aggregation is described quantitatively by the [[DLVO theory]].<ref>{{Cite journal|date=2011-01-01|title=Intermolecular Force|journal=Interface Science and Technology|volume=18|pages=1–57|doi=10.1016/B978-0-12-375049-5.00001-3|last1=Park|first1=Soo-Jin|last2=Seo|first2=Min-Kang|bibcode=2011IntST..18....1P |isbn=978-0-12-375049-5}}</ref> A common method of stabilising a colloid (converting it from a precipitate) is [[peptization]], a process where it is shaken with an electrolyte. | ||
* Steric stabilization consists absorbing a layer of a polymer or surfactant on the particles to prevent them from getting close in the range of attractive forces.<ref name="cosgrove2010" /> The polymer consists of chains that are attached to the particle surface, and the part of the chain that extends out is soluble in the suspension medium.<ref>{{Cite book|title=Colloid stability : the role of surface forces. Part I|date=2007|publisher=Wiley-VCH|author=Tadros, Tharwat F. |isbn=978-3-527-63107-0|location=Weinheim|oclc=701308697}}</ref> This technique is used to stabilize colloidal particles in all types of solvents, including organic solvents.<ref>{{Cite journal|last1=Genz|first1=Ulrike|last2=D'Aguanno|first2=Bruno|last3=Mewis|first3=Jan|last4=Klein|first4=Rudolf|date=1994-07-01|title=Structure of Sterically Stabilized Colloids|journal=Langmuir|volume=10|issue=7|pages=2206–2212|doi=10.1021/la00019a029}}</ref> | * Steric stabilization consists absorbing a layer of a polymer or surfactant on the particles to prevent them from getting close in the range of attractive forces.<ref name="cosgrove2010" /> The polymer consists of chains that are attached to the particle surface, and the part of the chain that extends out is soluble in the suspension medium.<ref>{{Cite book|title=Colloid stability: the role of surface forces. Part I|date=2007|publisher=Wiley-VCH|author=Tadros, Tharwat F. |isbn=978-3-527-63107-0|location=Weinheim|oclc=701308697}}</ref> This technique is used to stabilize colloidal particles in all types of solvents, including organic solvents.<ref>{{Cite journal|last1=Genz|first1=Ulrike|last2=D'Aguanno|first2=Bruno|last3=Mewis|first3=Jan|last4=Klein|first4=Rudolf|date=1994-07-01|title=Structure of Sterically Stabilized Colloids|journal=Langmuir|volume=10|issue=7|pages=2206–2212|doi=10.1021/la00019a029}}</ref> | ||
A combination of the two mechanisms is also possible (electrosteric stabilization). | A combination of the two mechanisms is also possible (electrosteric stabilization). | ||
| Line 136: | Line 154: | ||
=== Destabilization === | === Destabilization === | ||
Destabilization can be accomplished by different methods: | Destabilization can be accomplished by 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 to reduce the [[Debye length|Debye screening length]] (the width of the electrical double layer) of the particles. It is also accomplished by changing the pH of a suspension to effectively neutralise the surface charge of the particles in suspension.<ref name="Israelachvili-2011" /> This removes the repulsive forces that keep colloidal particles separate and allows for aggregation due to van der Waals forces. Minor changes in pH can manifest in significant alteration to the [[zeta potential]]. When the magnitude of the zeta potential lies below a certain threshold, typically around ± 5mV, rapid coagulation or aggregation tends to occur.<ref>{{Cite journal|last1=Bean|first1=Elwood L.|last2=Campbell|first2=Sylvester J.|last3=Anspach|first3=Frederick R.|last4=Ockershausen|first4=Richard W.|last5=Peterman|first5=Charles J.|date=1964|title=Zeta Potential Measurements in the Control of Coagulation Chemical Doses [with Discussion] | *Removal of the electrostatic barrier that prevents aggregation of the particles. This can be accomplished by the addition of salt to a suspension to reduce the [[Debye length|Debye screening length]] (the width of the electrical double layer) of the particles. It is also accomplished by changing the pH of a suspension to effectively neutralise the surface charge of the particles in suspension.<ref name="Israelachvili-2011" /> This removes the repulsive forces that keep colloidal particles separate and allows for aggregation due to van der Waals forces. Minor changes in pH can manifest in significant alteration to the [[zeta potential]]. When the magnitude of the zeta potential lies below a certain threshold, typically around ± 5mV, rapid coagulation or aggregation tends to occur.<ref>{{Cite journal|last1=Bean|first1=Elwood L.|last2=Campbell|first2=Sylvester J.|last3=Anspach|first3=Frederick R.|last4=Ockershausen|first4=Richard W.|last5=Peterman|first5=Charles J.|date=1964|title=Zeta Potential Measurements in the Control of Coagulation Chemical Doses [with Discussion]|journal=Journal (American Water Works Association)|volume=56|issue=2|pages=214–227|doi=10.1002/j.1551-8833.1964.tb01202.x|jstor=41264141}}</ref> | ||
*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 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 [[Depletion force|depletants]] that cause aggregation due to entropic effects. | *Addition of non-adsorbed polymers called [[Depletion force|depletants]] that cause aggregation due to entropic effects. | ||
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[[File:MLS scan.gif|thumb|Measurement principle of multiple light scattering coupled with vertical scanning]] | [[File:MLS scan.gif|thumb|Measurement principle of multiple light scattering coupled with vertical scanning]] | ||
The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple [[light scattering]] coupled with vertical scanning.<ref>{{cite journal|doi=10.1016/S0378-5173(03)00364-8|title=Systematic characterisation of oil-in-water emulsions for formulation design|year=2003|last1=Roland|first1=I|journal=International Journal of Pharmaceutics|volume=263|pages=85–94|pmid=12954183|last2=Piel|first2=G|last3=Delattre|first3=L|last4=Evrard|first4=B|issue=1–2}}</ref><ref>{{cite journal|doi=10.1023/A:1025017502379|year=2003|last1=Lemarchand|first1=Caroline|last2=Couvreur|first2=Patrick|last3=Besnard|first3=Madeleine|last4=Costantini|first4=Dominique|last5=Gref|first5=Ruxandra|s2cid=24157992|journal=Pharmaceutical Research|volume=20|pages=1284–92|pmid=12948027|title=Novel polyester-polysaccharide nanoparticles|issue=8}}</ref><ref>{{cite journal|doi=10.1016/S0927-7757(98)00680-3|title=Characterisation of instability of concentrated dispersions by a new optical analyser: the TURBISCAN MA 1000|year=1999|last1=Mengual|first1=O|journal=Colloids and Surfaces A: Physicochemical and Engineering Aspects|volume=152|issue=1–2|pages=111–123 }}</ref><ref>{{cite book|author=Bru, P. |title= Particle sizing and characterisation|editor1=T. Provder |editor2=J. Texter |year=2004|display-authors=etal}}</ref> This method, known as [[turbidimetry]], is based on measuring the fraction of light that, after being sent through the sample, | The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple [[light scattering]] coupled with vertical scanning.<ref>{{cite journal|doi=10.1016/S0378-5173(03)00364-8|title=Systematic characterisation of oil-in-water emulsions for formulation design|year=2003|last1=Roland|first1=I|journal=International Journal of Pharmaceutics|volume=263|pages=85–94|pmid=12954183|last2=Piel|first2=G|last3=Delattre|first3=L|last4=Evrard|first4=B|issue=1–2}}</ref><ref>{{cite journal|doi=10.1023/A:1025017502379|year=2003|last1=Lemarchand|first1=Caroline|last2=Couvreur|first2=Patrick|last3=Besnard|first3=Madeleine|last4=Costantini|first4=Dominique|last5=Gref|first5=Ruxandra|s2cid=24157992|journal=Pharmaceutical Research|volume=20|pages=1284–92|pmid=12948027|title=Novel polyester-polysaccharide nanoparticles|issue=8}}</ref><ref>{{cite journal|doi=10.1016/S0927-7757(98)00680-3|title=Characterisation of instability of concentrated dispersions by a new optical analyser: the TURBISCAN MA 1000|year=1999|last1=Mengual|first1=O|journal=Colloids and Surfaces A: Physicochemical and Engineering Aspects|volume=152|issue=1–2|pages=111–123 }}</ref><ref>{{cite book|author=Bru, P. |title= Particle sizing and characterisation|editor1=T. Provder |editor2=J. Texter |year=2004|display-authors=etal}}</ref> This method, known as [[turbidimetry]], is based on measuring the fraction of light that, after being sent through the sample, is backscattered by the colloidal particles. The backscattering intensity is directly proportional to the average particle size and volume fraction of the dispersed phase. Therefore, local changes in concentration caused by sedimentation or creaming, and clumping together of particles caused by aggregation, are detected and monitored.<ref>{{Cite journal|last1=Matusiak|first1=Jakub|last2=Grządka|first2=Elżbieta|date=2017-12-08|title=Stability of colloidal systems - a review of the stability measurements methods|url=https://journals.umcs.pl/aa/article/view/4877|journal=Annales Universitatis Mariae Curie-Skłodowska, Sectio AA – Chemia|volume=72|issue=1|page=33|doi=10.17951/aa.2017.72.1.33|doi-access=free}}</ref> These phenomena are associated with unstable colloids. | ||
[[Dynamic light scattering]] can be used to detect the size of a colloidal particle by measuring how fast they diffuse. This method involves directing laser light towards a colloid. The scattered light will form an interference pattern, and the fluctuation in light intensity in this pattern is caused by the Brownian motion of the particles. If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion. This technique can confirm that aggregation has occurred if the apparent particle size is determined to be beyond the typical size range for colloidal particles.<ref name="Everett-1988" /> | [[Dynamic light scattering]] can be used to detect the size of a colloidal particle by measuring how fast they diffuse. This method involves directing laser light towards a colloid. The scattered light will form an interference pattern, and the fluctuation in light intensity in this pattern is caused by the Brownian motion of the particles. If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion. This technique can confirm that aggregation has occurred if the apparent particle size is determined to be beyond the typical size range for colloidal particles.<ref name="Everett-1988" /> | ||
===Accelerating methods for shelf life prediction=== | ===Accelerating methods for shelf life prediction=== | ||
The kinetic process of destabilisation can be rather long (up to several months or years for some products). Thus, | The kinetic process of destabilisation can be rather long (up to several months or years for some products). Thus, further accelerating methods are often required, to enable the formulator to develop a new product design within a reasonable timeframe. Thermal methods are the most commonly used and consist of increasing temperature to accelerate destabilisation (below critical temperatures of phase inversion or chemical degradation). Temperature affects not only 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 makes it possible to simulate real-life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times. | ||
Mechanical acceleration including vibration, [[centrifugation]] 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. Some emulsions would never coalesce in normal gravity, while they do under artificial gravity.<ref>{{cite book|url=https://books.google.com/books?id=hDOS5OfL_pQC&pg=PA89|page=89|author= Salager, J-L |title=Pharmaceutical emulsions and suspensions|editor1=Françoise Nielloud |editor2=Gilberte Marti-Mestres |year=2000|isbn=978-0-8247-0304-2|publisher=CRC press}}</ref> Segregation of different populations of particles have been highlighted when using centrifugation and vibration.<ref>{{cite journal|doi=10.1021/la802459u|title=Size Segregation in a Fluid-like or Gel-like Suspension Settling under Gravity or in a Centrifuge|year=2008|last1=Snabre|first1=Patrick|last2=Pouligny|first2=Bernard|journal=Langmuir|volume=24|pages=13338–47|pmid=18986182|issue=23}}</ref> | Mechanical acceleration including vibration, [[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. Some emulsions would never coalesce in normal gravity, while they do under artificial gravity.<ref>{{cite book|url=https://books.google.com/books?id=hDOS5OfL_pQC&pg=PA89|page=89|author= Salager, J-L |title=Pharmaceutical emulsions and suspensions|editor1=Françoise Nielloud |editor2=Gilberte Marti-Mestres |year=2000|isbn=978-0-8247-0304-2|publisher=CRC press}}</ref> Segregation of different populations of particles have been highlighted when using centrifugation and vibration.<ref>{{cite journal|doi=10.1021/la802459u|title=Size Segregation in a Fluid-like or Gel-like Suspension Settling under Gravity or in a Centrifuge|year=2008|last1=Snabre|first1=Patrick|last2=Pouligny|first2=Bernard|journal=Langmuir|volume=24|pages=13338–47|pmid=18986182|issue=23}}</ref> | ||
==As a model system for atoms== | ==As a model system for atoms== | ||
In [[physics]], colloids are an interesting model system for [[atom]]s.<ref>{{cite journal|last=Manoharan| first=Vinothan N. |title=Colloidal matter: Packing, geometry, and entropy| journal=Science| volume=349| issue=6251 | | In [[physics]], colloids are an interesting model system for [[atom]]s.<ref>{{cite journal|last=Manoharan| first=Vinothan N. |title=Colloidal matter: Packing, geometry, and entropy| journal=Science| volume=349| issue=6251 | article-number=1253751| date=2015| doi=10.1126/science.1253751| pmid=26315444| s2cid=5727282 | url=https://dash.harvard.edu/bitstream/handle/1/30410808/Manoharan-Science-2015-postprint.pdf?sequence=1| doi-access=free}}</ref> Micrometre-scale colloidal particles are large enough to be observed by optical techniques such as [[confocal microscopy]]. 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 of colloidal suspensions. For example, the same techniques used to model ideal gases can be applied to [[Scientific modelling|model]] the behavior of a hard sphere colloidal suspension. [[Phase transition]]s in colloidal suspensions can be studied in real time using optical techniques,<ref name=greenfield2013shockwave>{{cite journal|last=Greenfield|first=Elad |author2=Nemirovsky, Jonathan |author3=El-Ganainy, Ramy |author4=Christodoulides, Demetri N |author5=Segev, Mordechai |title=Shockwave based nonlinear optical manipulation in densely scattering opaque suspensions|journal=Optics Express|year=2013|volume=21|issue=20|pages=23785–23802|doi=10.1364/OE.21.023785 | pmid = 24104290 |bibcode = 2013OExpr..2123785G |url=https://stars.library.ucf.edu/cgi/viewcontent.cgi?article=5052&context=facultybib2010 |doi-access=free }}</ref> and are analogous to phase transitions in liquids. In many interesting cases optical fluidity is used to control colloid suspensions.<ref name=greenfield2013shockwave /><ref name=greenfield2011light>{{cite journal|last=Greenfield|first=Elad |author2=Rotschild, Carmel |author3=Szameit, Alexander |author4=Nemirovsky, Jonathan |author5=El-Ganainy, Ramy |author6=Christodoulides, Demetrios N |author7=Saraf, Meirav |author8=Lifshitz, Efrat |author9=Segev, Mordechai |title=Light-induced self-synchronizing flow patterns|journal=New Journal of Physics|year=2011|volume=13|issue=5|article-number=053021|doi=10.1088/1367-2630/13/5/053021|bibcode = 2011NJPh...13e3021G |doi-access=free }}</ref> | ||
==Crystals== | ==Crystals== | ||
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A colloidal crystal is a highly [[Order (crystal lattice)|ordered]] array of particles that can be formed over a very long range (typically on the order of a few millimeters to one centimeter) and that appear [[analogous]] to their atomic or molecular counterparts.<ref>{{cite journal|author =Pieranski, P.|year =1983| title = Colloidal Crystals| journal= Contemporary Physics| volume= 24| pages =25–73|doi =10.1080/00107518308227471|bibcode = 1983ConPh..24...25P }}</ref> One of the finest [[natural]] examples of this ordering phenomenon can be found in precious [[opal]], in which brilliant regions of pure [[wikt:spectrum|spectral]] [[color]] result from [[close-packed]] domains of [[amorphous]] colloidal spheres of [[silicon dioxide]] (or [[silica]], SiO<sub>2</sub>).<ref>{{cite journal|author = Sanders, J.V.|year =1964|title = Structure of Opal|journal = Nature |volume=204|page =1151|doi=10.1038/204990a0|last2 = Sanders|first2 = J. V.|last3 = Segnit|first3 = E. R.|s2cid =4191566|bibcode = 1964Natur.204..990J|issue=4962}}</ref><ref>{{cite journal|author = Darragh, P.J.|year =1976|journal = Scientific American|volume=234|issue =4|pages=84–95|display-authors=etal|doi=10.1038/scientificamerican0476-84|title=Opals|bibcode=1976SciAm.234d..84D}}</ref> These spherical particles [[precipitate]] in highly [[siliceous]] pools in [[Australia]] and elsewhere, and form these highly ordered arrays after years of [[sedimentation]] and [[compression (physical)|compression]] under [[hydrostatic]] and gravitational forces. The periodic arrays of submicrometre spherical particles provide similar arrays of [[interstitial defect|interstitial]] [[wikt:void|voids]], which act as a natural [[diffraction grating]] for [[visible spectrum|visible]] [[light]] [[wave]]s, particularly when the interstitial spacing is of the same [[order of magnitude]] as the [[Optical physics|incident]] lightwave.<ref>{{cite journal |last1=Luck |first1=Werner |last2=Klier |first2=Manfred |last3=Wesslau |first3=Hermann |title=Über Bragg-Reflexe mit sichtbarem Licht an monodispersen Kunststofflatices. II |journal=Berichte der Bunsengesellschaft für Physikalische Chemie |date= 1963 |volume=67 |issue=1 |pages=84–85 |doi=10.1002/bbpc.19630670114}}</ref><ref>{{cite journal|author1=Hiltner, P.A. |author2=Krieger, I.M.|year =1969|title = Diffraction of light by ordered suspensions|journal=J. Phys. Chem.|volume=73|page=2306|doi = 10.1021/j100727a049|issue = 7}}</ref> | A colloidal crystal is a highly [[Order (crystal lattice)|ordered]] array of particles that can be formed over a very long range (typically on the order of a few millimeters to one centimeter) and that appear [[analogous]] to their atomic or molecular counterparts.<ref>{{cite journal|author =Pieranski, P.|year =1983| title = Colloidal Crystals| journal= Contemporary Physics| volume= 24| pages =25–73|doi =10.1080/00107518308227471|bibcode = 1983ConPh..24...25P }}</ref> One of the finest [[natural]] examples of this ordering phenomenon can be found in precious [[opal]], in which brilliant regions of pure [[wikt:spectrum|spectral]] [[color]] result from [[close-packed]] domains of [[amorphous]] colloidal spheres of [[silicon dioxide]] (or [[silica]], SiO<sub>2</sub>).<ref>{{cite journal|author = Sanders, J.V.|year =1964|title = Structure of Opal|journal = Nature |volume=204|page =1151|doi=10.1038/204990a0|last2 = Sanders|first2 = J. V.|last3 = Segnit|first3 = E. R.|s2cid =4191566|bibcode = 1964Natur.204..990J|issue=4962}}</ref><ref>{{cite journal|author = Darragh, P.J.|year =1976|journal = Scientific American|volume=234|issue =4|pages=84–95|display-authors=etal|doi=10.1038/scientificamerican0476-84|title=Opals|bibcode=1976SciAm.234d..84D}}</ref> These spherical particles [[precipitate]] in highly [[siliceous]] pools in [[Australia]] and elsewhere, and form these highly ordered arrays after years of [[sedimentation]] and [[compression (physical)|compression]] under [[hydrostatic]] and gravitational forces. The periodic arrays of submicrometre spherical particles provide similar arrays of [[interstitial defect|interstitial]] [[wikt:void|voids]], which act as a natural [[diffraction grating]] for [[visible spectrum|visible]] [[light]] [[wave]]s, particularly when the interstitial spacing is of the same [[order of magnitude]] as the [[Optical physics|incident]] lightwave.<ref>{{cite journal |last1=Luck |first1=Werner |last2=Klier |first2=Manfred |last3=Wesslau |first3=Hermann |title=Über Bragg-Reflexe mit sichtbarem Licht an monodispersen Kunststofflatices. II |journal=Berichte der Bunsengesellschaft für Physikalische Chemie |date= 1963 |volume=67 |issue=1 |pages=84–85 |doi=10.1002/bbpc.19630670114}}</ref><ref>{{cite journal|author1=Hiltner, P.A. |author2=Krieger, I.M.|year =1969|title = Diffraction of light by ordered suspensions|journal=J. Phys. Chem.|volume=73|page=2306|doi = 10.1021/j100727a049|issue = 7}}</ref> | ||
Thus, it has been known for many years that, due to [[Coulomb's Law|repulsive]] [[Coulombic]] interactions, [[electrically charged]] [[macromolecule]]s in an [[aqueous]] environment can exhibit long-range [[crystal]]-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 [[ | Thus, it has been known for many years that, due to [[Coulomb's Law|repulsive]] [[Coulombic]] interactions, [[electrically charged]] [[macromolecule]]s in an [[aqueous]] environment can exhibit long-range [[crystal]]-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 [[Bragg's law]], in a matter analogous to the [[scattering]] of [[X-ray]]s in crystalline solids. | ||
The large number of experiments exploring the [[physics]] and [[chemistry]] of 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 polymer and mineral) and, through various mechanisms, implementing and preserving their long-range order formation.<ref>{{Cite journal|last1=Liu|first1=Xuesong|last2=Li|first2=Zejing|last3=Tang|first3=Jianguo|last4=Yu|first4=Bing|last5=Cong|first5=Hailin|date=2013-09-09|title=Current status and future developments in preparation and application of colloidal crystals|journal=Chemical Society Reviews|volume=42|issue=19|pages=7774–7800|doi=10.1039/C3CS60078E|pmid=23836297}}</ref> | The large number of experiments exploring the [[physics]] and [[chemistry]] of 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 polymer and mineral) and, through various mechanisms, implementing and preserving their long-range order formation.<ref>{{Cite journal|last1=Liu|first1=Xuesong|last2=Li|first2=Zejing|last3=Tang|first3=Jianguo|last4=Yu|first4=Bing|last5=Cong|first5=Hailin|date=2013-09-09|title=Current status and future developments in preparation and application of colloidal crystals|journal=Chemical Society Reviews|volume=42|issue=19|pages=7774–7800|doi=10.1039/C3CS60078E|pmid=23836297}}</ref> | ||
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==In biology== | ==In biology== | ||
Colloidal [[phase separation]] is an important organising principle for compartmentalisation of both the [[cytoplasm]] and [[Cell nucleus|nucleus]] of cells into '''[[biomolecular condensate]]s'''—similar in importance to compartmentalisation via lipid bilayer [[biological membranes|membranes]], a type of [[liquid crystal]]. The term [[biomolecular condensate]] has been used to refer to clusters of [[macromolecules]] that arise via liquid-liquid or liquid-solid [[phase separation]] within cells. [[Macromolecular crowding]] strongly enhances colloidal phase separation and formation of [[biomolecular condensate]]s. | Colloidal [[phase separation]] is an important organising principle for compartmentalisation of both the [[cytoplasm]] and [[Cell nucleus|nucleus]] of cells into '''[[biomolecular condensate]]s'''—similar in importance to compartmentalisation via lipid bilayer [[biological membranes|membranes]], a type of [[liquid crystal]]. The term [[biomolecular condensate]] has been used to refer to clusters of [[macromolecules]] that arise via liquid-liquid or liquid-solid [[phase separation]] within cells. [[Macromolecular crowding]] strongly enhances colloidal phase separation and formation of [[biomolecular condensate]]s. | ||
Colloidal solutions are also used as a tool enabling fast, simple, and safe intracellular delivery of various types of molecules, such as polymers or proteins.<ref>{{cite journal |last1=Karpińska |first1=Aneta |last2=Zgorzelska |first2=Alicja |last3=Kwapiszewska |first3=Karina |last4=Hołyst |first4=Robert |title=Entanglement of polymer chains in hypertonic medium enhances the delivery of DNA and other biomacromolecules into cells |journal=Journal of Colloid and Interface Science |date=December 2022 |volume=627 |pages=270–282 |doi=10.1016/j.jcis.2022.07.040|doi-access=free }}</ref> | |||
==In the environment== | ==In the environment== | ||
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|archive-url = https://web.archive.org/web/20090309172632/http://www.nagra.ch/documents/database/dokumente/%24default/Default%20Folder/Publikationen/e%5Fntb02%2D14.pdf | |archive-url = https://web.archive.org/web/20090309172632/http://www.nagra.ch/documents/database/dokumente/%24default/Default%20Folder/Publikationen/e%5Fntb02%2D14.pdf | ||
|archive-date = 9 March 2009 | |archive-date = 9 March 2009 | ||
}}</ref> | }}</ref> | ||
because of the process of [[ultrafiltration]] occurring in dense clay membrane.<ref>{{Cite web | because of the process of [[ultrafiltration]] occurring in dense clay membrane.<ref>{{Cite web | ||
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|url = http://www.kth.se/che/divisions/nuchem/research/1.19965?l=en_UK | |url = http://www.kth.se/che/divisions/nuchem/research/1.19965?l=en_UK | ||
|access-date = 12 February 2009 | |access-date = 12 February 2009 | ||
|archive-url = https://web.archive.org/web/20090304210603/http://www.kth.se/che/divisions/nuchem/research/1.19965?l=en_UK | |archive-url = https://web.archive.org/web/20090304210603/http://www.kth.se/che/divisions/nuchem/research/1.19965?l=en_UK | ||
|archive-date = 4 March 2009 | |archive-date = 4 March 2009 | ||
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| pages = 477–484|bibcode = 2007PCE....32..477W }}</ref> | | pages = 477–484|bibcode = 2007PCE....32..477W }}</ref> | ||
In [[soil science]], the colloidal fraction in [[soil]]s consists of tiny [[clay]] and [[humus]] [[particle]]s that are less than 1μm in [[diameter]] and carry either positive and/or negative [[Electric charge|electrostatic charges]] that vary depending on the chemical conditions of the soil sample, i.e. [[soil pH]].<ref>{{Cite book|title=Elements of the nature and properties of soils|author1=Weil, Ray|author2=Brady, Nyle C.|isbn= | In [[soil science]], the colloidal fraction in [[soil]]s consists of tiny [[clay]] and [[humus]] [[particle]]s that are less than 1μm in [[diameter]] and carry either positive and/or negative [[Electric charge|electrostatic charges]] that vary depending on the chemical conditions of the soil sample, i.e. [[soil pH]].<ref>{{Cite book|title=Elements of the nature and properties of soils|author1=Weil, Ray|author2=Brady, Nyle C.|isbn=978-0-13-325459-4|edition= Fourth|location=New York, NY|oclc=1035317420|date = 11 October 2018}}</ref> | ||
==Intravenous therapy== | ==Intravenous therapy== | ||
Colloid solutions used in [[intravenous therapy]] belong to a major group of [[volume expander]]s, and can be used for intravenous [[fluid replacement]]. Colloids preserve a high [[colloid osmotic pressure]] in the blood,<ref name="gregory">{{Cite web|url=http://www.medscape.org/viewarticle/503138|title=An Update on Intravenous Fluids|last=Martin|first=Gregory S.|date=19 April 2005|website=[[Medscape]]|access-date=6 July 2016}}</ref> and therefore, they should theoretically preferentially increase the [[intravascular volume]], whereas other types of volume expanders called [[crystalloid solution|crystalloid]]s also increase the [[interstitial volume]] and [[intracellular volume]]. However, there is still controversy to the actual difference in [[efficacy]] by this difference,<ref name=gregory/> and much of the research related to this use of colloids is based on fraudulent research by [[Joachim Boldt]].<ref>{{Cite news|url=https://www.telegraph.co.uk/health/8360667/Millions-of-surgery-patients-at-risk-in-drug-research-fraud-scandal.html|title=Millions of surgery patients at risk in drug research fraud scandal|last=Blake|first=Heidi|date=3 March 2011|newspaper=The Telegraph|location=UK|archive-url=https://web.archive.org/web/20111104083124/http://www.telegraph.co.uk/health/8360667/Millions-of-surgery-patients-at-risk-in-drug-research-fraud-scandal.html|archive-date=4 November 2011 | Colloid solutions used in [[intravenous therapy]] belong to a major group of [[volume expander]]s, and can be used for intravenous [[fluid replacement]]. Colloids preserve a high [[colloid osmotic pressure]] in the blood,<ref name="gregory">{{Cite web|url=http://www.medscape.org/viewarticle/503138|title=An Update on Intravenous Fluids|last=Martin|first=Gregory S.|date=19 April 2005|website=[[Medscape]]|access-date=6 July 2016}}</ref> and therefore, they should theoretically preferentially increase the [[intravascular volume]], whereas other types of volume expanders called [[crystalloid solution|crystalloid]]s also increase the [[interstitial volume]] and [[intracellular volume]]. However, there is still controversy to the actual difference in [[efficacy]] by this difference,<ref name=gregory/> and much of the research related to this use of colloids is based on fraudulent research by [[Joachim Boldt]].<ref>{{Cite news|url=https://www.telegraph.co.uk/health/8360667/Millions-of-surgery-patients-at-risk-in-drug-research-fraud-scandal.html|title=Millions of surgery patients at risk in drug research fraud scandal|last=Blake|first=Heidi|date=3 March 2011|newspaper=The Telegraph|location=UK|archive-url=https://web.archive.org/web/20111104083124/http://www.telegraph.co.uk/health/8360667/Millions-of-surgery-patients-at-risk-in-drug-research-fraud-scandal.html|archive-date=4 November 2011|access-date=4 November 2011}}</ref> Another difference is that crystalloids generally are much cheaper than colloids.<ref name=gregory/> | ||
==References== | ==References== | ||