A Barrer is a non-SI

Si

Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...

 unit of gas permeability

Semipermeable membrane

A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...

 (specifically, oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 permeability) used in the contact lens

Contact lens

A contact lens, or simply contact, is a lens placed on the eye. They are considered medical devices and can be worn to correct vision, for cosmetic or therapeutic reasons. In 2004, it was estimated that 125 million people use contact lenses worldwide, including 28 to 38 million in the United...

 industry. It is a bulk property. It is named after Richard Barrer.

Definition

1 Barrer = 10^-11 (cm³ O₂ ) cm cm^-2 s^-1 mmHg

Torr

The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...

^-1. or
1 Barrer = 10^-10 (cm³ O₂ ) cm cm^-2 s^-1 cmHg

Torr

The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...

^-1.
Here 'cm³ O₂' represents a molar quantity

Mole (unit)

The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...

 of oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 rather than a true volume

Volume

Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....

. It represents the quantity of oxygen that would take up one cubic centimeter at standard temperature and pressure

Standard conditions for temperature and pressure

Standard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data...

, as calculated via the ideal gas law

Ideal gas law

The ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behavior of many gases under many conditions, although it has several limitations. It was first stated by Émile Clapeyron in 1834 as a combination of Boyle's law and Charles's law...

.


The 'cm' represents the thickness of the material whose permeability is being evaluated, and cm^-2 is the reciprocal of the surface area of that material.

1 Barrer = 846 millilitre . mm / (cm² . day. bar(a))



1 Barrer = 3.348 x 10^-19 kmol m / (m² s Pa)

External links

• How Dk is measured, and is there a certifiable standard? ('Dk' is an equivalent term to 'permeability'.)
• S. A. Stern, 'The barrer permeability unit', Journal of Polymer Science Part A-2: Polymer Physics,Volume 6, Issue 11 , Pages 1933 - 1934