Editing Emulsion (section)

{{Short description|Mixture of two or more immiscible liquids}}
{{About|mixtures of liquids|the light-sensitive mixture used in photography|Photographic emulsion}}
[[File:Emulsions.svg|frame|right| {{ordered list |list_style_type=upper-alpha
    |1=<!--A-->Two immiscible liquids, not yet emulsified
    |2=<!--B-->An emulsion of Phase II dispersed in Phase I
    |3=<!--C-->The unstable emulsion progressively separates
    |4=<!--D-->The [[surfactant]] (outline around particles) positions itself on the interfaces between Phase II and Phase I, stabilizing the emulsion
}}]]

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

Two liquids can form different types of emulsions. As an example, oil and water can form, first, an oil-in-water emulsion, in which the oil is the dispersed phase, and water is the continuous phase. Second, they can form a water-in-oil emulsion, in which water is the dispersed phase and oil is the continuous phase. Multiple emulsions are also possible, including a "water-in-oil-in-water" emulsion and an "oil-in-water-in-oil" emulsion.<ref>{{cite journal|pmid=17076645 |year=2006 |last1=Khan |first1=A. Y. |title=Multiple emulsions: An overview |journal=Current Drug Delivery |volume=3 |issue=4 |pages=429–43 |last2=Talegaonkar |first2=S |last3=Iqbal |first3=Z |last4=Ahmed |first4=F. J. |last5=Khar |first5=R. K. |doi=10.2174/156720106778559056}}</ref>

Emulsions, being liquids, do not exhibit a static internal structure. The droplets dispersed in the continuous phase (sometimes referred to as the "dispersion medium") are usually assumed to be [[Probability distribution|statistically distributed]] to produce roughly spherical droplets.

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

{{Quote box
 |title =[[International Union of Pure and Applied Chemistry|IUPAC]] 
 |quote = A fluid system in which liquid droplets are dispersed in a liquid.

''Note 1'': The definition is based on the definition in ref.<ref>{{cite book|title=Compendium of Chemical Terminology (The "Gold Book")|year=1997|publisher=[[Blackwell Scientific Publications]]|location=Oxford|author=IUPAC|chapter-url=http://goldbook.iupac.org/E02065.html|url-status=dead |archive-url= https://web.archive.org/web/20120310221658/http://goldbook.iupac.org/E02065.html|archive-date=2012-03-10 |doi=10.1351/goldbook.E02065 |chapter=Emulsion|isbn=978-0-9678550-9-7}}</ref>

''Note 2'': The droplets may be amorphous, liquid-crystalline, or any<br/>mixture thereof.

''Note 3'': The diameters of the droplets constituting the ''[[Dispersion (chemistry)|dispersed phase]]''<br/>usually range from approximately 10&nbsp;nm to 100&nbsp;μm; i.e., the droplets<br/>may exceed the usual size limits for [[colloid]]al particles.

''Note 4'': An emulsion is termed an oil/water (o/w) emulsion if the<br/>dispersed phase is an organic material and the ''continuous phase'' is<br/>water or an aqueous solution and is termed water/oil (w/o) if the dispersed<br/>phase is water or an aqueous solution and the continuous phase is an<br/>organic liquid (an "oil").

''Note 5'': A w/o emulsion is sometimes called an inverse emulsion.<br/>The term "inverse emulsion" is misleading, suggesting incorrectly that<br/>the emulsion has properties that are the opposite of those of an emulsion.<br/>Its use is, therefore, not recommended.<ref>{{cite journal|title=Terminology of polymers 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 |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|url=https://espace.library.uq.edu.au/view/UQ:266979/UQ266979_OA.pdf}}</ref>
}}