Barrer
3236606
219808465
2008-06-16T23:33:36Z
144.53.251.2
/* Definition */ rm SI conversion (see Talk)
A '''Barrer''' is a non-[[SI]] unit of gas [[Semipermeable membrane|permeability]] (specifically, [[oxygen]] permeability) used in the [[contact lens]] industry. It is a [[bulk property]]. It is named after [[Permeation#Richard Barrer .281910 - 1996.29|Richard Barrer]].
==Definition==
1 Barrer = 10<sup>-11</sup> (cm<sup>3</sup> O<sub>2</sub> ) cm cm<sup>-2</sup> s<sup>-1</sup> [[Torr|mmHg]]<sup>-1</sup>.
Here 'cm<sup>3</sup> O<sub>2</sub>' represents a [[Mole (unit)|molar quantity]] of [[oxygen]] rather than a true [[volume]]. It represents the quantity of oxygen that ''would'' take up one cubic centimeter at [[Standard conditions for temperature and pressure|standard temperature and pressure]], as calculated via the [[ideal gas law]].
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The 'cm' represents the thickness of the material whose permeability is being evaluated, and cm<sup>-2</sup> is the reciprocal of the surface area of that material.
1 Barrer = 846 [[millilitre]] . mm / (cm<sup>2</sup> . day. bar(a))
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1 [[Bar (unit)|bar]] (a) = 1 bars absolute (with respect to vacuum)
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==External links==
*[http://www.siliconehydrogels.org/editorials/may_05.asp How Dk is measured, and is there a certifiable standard?] ('Dk' is an equivalent term to 'permeability'.)
*[http://www3.interscience.wiley.com/cgi-bin/abstract/104043309/ABSTRACT?CRETRY=1&SRETRY=0 S. A. Stern, 'The barrer permeability unit', Journal of Polymer Science Part A-2: Polymer Physics,Volume 6, Issue 11 , Pages 1933 - 1934]
[[Category:Units of measure]]
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