Supersaturation

Enormous, highly pure, single crystal substances can be grownfrom a solution at the metastable boundary between an unsatu-rated and supersaturated solution(Homogenous mixture). Here,a monopotassium phosphate crystal grown to create frequencydoubling optics for the NIF laser.

Supersaturation is a state of a solution that containsmore of the dissolved material than could be dissolvedby the solvent under normal circumstances. It can alsorefer to a vapor of a compound that has a higher (partial)pressure than the vapor pressure of that compound.

1 Condensation

Very small particles (seeds) can trigger the separation ofthe dissolved material from the solvent or condensationof the vapor. Seeds triggering the conversion of vaporare referred to as condensation nuclei, as in the case ofwater vapor. In the solid form these seeds can lead to theformation of crystallites or even large single crystals.

2 Preparation

Supersaturated solutions are prepared or result whensome condition of a saturated solution is changed, forexample decreasing (or, rarely, increasing) temperature,decreasing volume of the saturated solvent (as by liquidevaporation), or increasing pressure.

The supersaturation of sugar in water allows for rock candy toform.

Example of Supersaturation and Undersaturation due to Heatingor Cooling.

Example of Supersaturation and Undersaturation due to Produc-tion or Consumption (e.g., photosynthesis consumes carbon diox-ide and produces oxygen, whereas respiration consumes oxygenand produces carbon dioxide)

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2 6 REFERENCES

Example of Supersaturation andUndersaturation due to Pressureincreases or decreases. Causes may be due to: (1) Changes in airpressure (e.g., bubbles, storm systems); (2) Changes in gas mixingratio (e.g., fossil fuel CO2 pollutants)

3 Examples

Carbonated water is a supersaturated solution of carbondioxide gas in water. At the elevated pressure in thebottle, more carbon dioxide can dissolve in water thanat atmospheric pressure. At atmospheric pressure, thecarbon dioxide gas escapes very slowly from the super-saturated liquid. This process may be accelerated by thepresence of nucleation sites within the solution, such assmall bubbles, caused by shaking the bottle, or anothersolute, such as sugar powder or a widget. A Diet Cokeand Mentos eruption is a rather extreme example. Somebeverage products such as ales and stouts, e.g. Guinness,rely on this effect to produce the 'head' on the surfaceof the poured product. This has led to the invention ofthe widget, a device developed to produce enhanced bub-ble seeding in liquids, especially with dual supersaturatedgas phases (carbon dioxide and nitrogen) (see patents byNicholas Fitzpatrick and Kuzniarski).Scuba divers’ tissues become saturated with breathinggases during a dive. Supersaturation is a theoretical termdescribing a state in which the tension of a dissolvedgas is greater than its inspired partial pressure when thediver ascends, in contrast to Henry’s law.[1] If the diverascends too fast, these gases form bubbles, resulting indecompression sickness.[2] The term was popularized byJ.S. Haldane.[1][3]

In air that is supersaturated, water droplets may precip-itate upon being disturbed. This can be observed in acloud chamber. In the more general context a precipitatemay form.Supersaturated solutions of sugar and water are com-monly used to make rock candy.A supersaturated sodium acetate solution is used in sometypes of hand warmers.Supersaturation has also been gaining momentum as aformulation concept in pharmaceutical sciences. So-called supersaturating drug delivery systems (SSDS) are

a promising to obtain adequate oral bioavailability ofpoorly water- soluble drugs. Contemporary pharmaceu-tical pipelines are often highly populated with poorlywater-soluble drug candidates necessitating novel formu-lation technologies to provide dosage forms with appro-priate biopharmaceutical properties. SDDS contain thedrug in a high energy or otherwise rapidly dissolving formsuch that intraluminal concentrations above the satura-tion solubility of the drug are generated. For the strat-egy to be useful, the formed supersaturated solution mustthen be stabilized to allow for significant absorption andeventually sufficient bioavailability. The stabilization ofa supersaturated solution can be accomplished by addingprecipitation inhibitors which may act through a varietyof mechanisms.[4]

4 Gallery

5 See also• Supercooling

• Superheating

• Supersaturated design

6 References[1] Glossary of diving and hyperbaric terms. Undersea and

Hyperbaric Medical Society. 1978. ISBN 0-930406-01-X.

[2] Thalmann ED, Parker EC, Survanshi SS, Weathersby PK(1997). “Improved probabilistic decompression modelrisk predictions using linear-exponential kinetics”. Un-dersea and Hyperbaric Medicine 24 (4): 255–74. PMID9444058. Retrieved 2009-03-11.

[3] Boycott, A. E.; G. C. C. Damant, John Scott Hal-dane. (1908). “The Prevention of Compressed-air Illness”. Journal of Hygiene 8 (3): 342–443.doi:10.1017/S0022172400003399. PMC 2167126.PMID 20474365. Retrieved 2009-05-31.

[4] http://onlinelibrary.wiley.com/doi/10.1002/jps.21650/full

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