Miscibility

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Diesel fuel is immiscible in water. The bright rainbow pattern is the result of thin-film interference.

Miscibility (

dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also applies to solids and gases. An example in liquids is the miscibility of water and ethanol as they mix in all proportions.[1]

By contrast, substances are said to be immiscible if there are certain proportions in which the mixture does not form a solution. For one example, oil is not soluble in water, so these two solvents are immiscible. As another example, butanone (methyl ethyl ketone) is significantly soluble in water, but these two solvents are also immiscible because in some proportions the mixture will separate into two phases.[2]

Organic compounds

In

hexanoic acid (with six) is practically insoluble,[5] as are longer fatty acids and other lipids; the very long carbon chains of lipids cause them almost always to be immiscible with water. Analogous situations occur for other functional groups such as aldehydes and ketones
.

Metals

Immiscible metals are unable to form alloys with each other. Typically, a mixture will be possible in the molten state, but upon freezing, the metals separate into layers. This property allows solid precipitates to be formed by rapidly freezing a molten mixture of immiscible metals. One example of immiscibility in metals is copper and cobalt, where rapid freezing to form solid precipitates has been used to create granular GMR materials.[6]

There also exist metals that are immiscible in the liquid state. One with industrial importance is that liquid

liquid-liquid extraction, whereby lead containing any amount of silver is melted with zinc. The silver migrates to the zinc, which is skimmed off the top of the two-phase liquid, and the zinc is then boiled away, leaving nearly pure silver.[7]

Effect of entropy

Main article: Hydrophobic effect

If a mixture of polymers has lower configurational entropy than the components, they are likely to be immiscible in one another even in the liquid state.[8][9]

Determination

Miscibility of two materials is often determined optically. When the two miscible liquids are combined, the resulting liquid is clear. If the mixture is cloudy the two materials are immiscible. Care must be taken with this determination. If the indices of refraction of the two materials are similar, an immiscible mixture may be clear and give an incorrect determination that the two liquids are miscible.[10]

See also

References

Wikimedia Commons has media related to Immiscible liquids.
  1. ISBN 0-13-033832-X
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  2. ISBN 9781483147123
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  3. ISBN 9780199655304
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  4. ISBN 9780471973973
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  5. ISBN 978-1439049143
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  6. ISBN 9780080510637
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  7. ISBN 9780857099945
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  8. ISBN 9780854043620
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  9. ISBN 9783527638499
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  10. ISBN 9780824797973
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