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Permeation 1 Permeation In physics and engineering, permeation (also called imbuing) is the penetration of a permeate (such as a liquid, gas, or vapor) through a solid. It is directly related to the concentration gradient of the permeate, a material's intrinsic permeability, and the materials' Mass diffusivity. Permeation is modeled by equations such as Fick's laws of diffusion, and can be measured using tools such as a minipermeameter. Description The process of permeation involves the diffusion of molecules, called the permeant, through a membrane or interface. Permeation works through diffusion; the permeant will move from high concentration to low concentration across the interface. A material can be semipermeable, with the presence of a semipermeable membrane. Only molecules or ions with certain properties will be able to diffuse across such a membrane. This is a very important mechanism in biology where fluids inside a blood vessel need to be regulated and controlled. Permeation can occur through most materials including metals, ceramics and polymers. However, the permeability of metals is much lower than that of ceramics and polymers due to their crystal structure and porosity. Permeation is something that must be regarded highly in various polymer applications, due to their high permeability. Permeability depends on the temperature of the interaction as well as the characteristics of both the polymer and the permeant component. Through the process of sorption, molecules of the permeant can be either absorbed or adsorbed at the interface. The permeation of a material can be measured through numerous methods that quantify the permeability of a substance through a specific material. Permeability is measured in units of area, commonly meters squared. It can be measured in a darcy or millidarcy popularized by Henry Darcy. They are not official SI units, however they are widely used. The permeability coefficient can be calculated in Barrers. Standard SI units for temperature, time, distance and pressure are used for the gasses and diffusion coefficients used to calculate permeability. Related terms Permeant: The substance or species, ion, molecules permeating through the solid. Semipermeability: Property of a material to be permeable only for some substances and not for others. Permeation measurement: Method for the quantification of the permeability of a material for a specific substance. History Abbé Jean-Antoine Nollet (physicist, 17001770) Nollet tried to seal wine containers with a pig's bladder and stored them under water. After a while the bladder bulged outwards. He noticed the high pressure that discharged after he pierced the bladder. Curious, he did the experiment the other way round: he filled the container with water and stored it in wine. The result was a bulging inwards of the bladder. His notes about this experiment are the first scientific mention of permeation (later it would be called semipermeability).

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Permeation theory and application

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Page 1: Permeation

Permeation 1

PermeationIn physics and engineering, permeation (also called imbuing) is the penetration of a permeate (such as a liquid, gas,or vapor) through a solid. It is directly related to the concentration gradient of the permeate, a material's intrinsicpermeability, and the materials' Mass diffusivity. Permeation is modeled by equations such as Fick's laws ofdiffusion, and can be measured using tools such as a minipermeameter.

DescriptionThe process of permeation involves the diffusion of molecules, called the permeant, through a membrane orinterface. Permeation works through diffusion; the permeant will move from high concentration to low concentrationacross the interface. A material can be semipermeable, with the presence of a semipermeable membrane. Onlymolecules or ions with certain properties will be able to diffuse across such a membrane. This is a very importantmechanism in biology where fluids inside a blood vessel need to be regulated and controlled. Permeation can occurthrough most materials including metals, ceramics and polymers. However, the permeability of metals is much lowerthan that of ceramics and polymers due to their crystal structure and porosity.Permeation is something that must be regarded highly in various polymer applications, due to their highpermeability. Permeability depends on the temperature of the interaction as well as the characteristics of both thepolymer and the permeant component. Through the process of sorption, molecules of the permeant can be eitherabsorbed or adsorbed at the interface. The permeation of a material can be measured through numerous methods thatquantify the permeability of a substance through a specific material.Permeability is measured in units of area, commonly meters squared. It can be measured in a darcy or millidarcypopularized by Henry Darcy. They are not official SI units, however they are widely used. The permeabilitycoefficient can be calculated in Barrers. Standard SI units for temperature, time, distance and pressure are used forthe gasses and diffusion coefficients used to calculate permeability.

Related terms•• Permeant: The substance or species, ion, molecules permeating through the solid.•• Semipermeability: Property of a material to be permeable only for some substances and not for others.•• Permeation measurement: Method for the quantification of the permeability of a material for a specific substance.

History

Abbé Jean-Antoine Nollet (physicist, 1700–1770)Nollet tried to seal wine containers with a pig's bladder and stored them under water. After a while the bladderbulged outwards. He noticed the high pressure that discharged after he pierced the bladder. Curious, he did theexperiment the other way round: he filled the container with water and stored it in wine. The result was a bulginginwards of the bladder. His notes about this experiment are the first scientific mention of permeation (later it wouldbe called semipermeability).

Page 2: Permeation

Permeation 2

Thomas Graham (chemist, 1805–1869)Graham experimentally proved the dependency of gas diffusion on molecular weight, which is now known asGraham's law.

Richard Barrer (1910–1996)Barrer developed the modern Barrer measurement technique, and first used scientific methods for measuringpermeation rates.

Permeation in everyday life• Packaging: The permeability of the package (materials, seals, closures, etc.) needs to be matched with the

sensitivity of the package contents and the specified shelf life. Some packages must have nearly hermetic sealswhile others can (and sometimes must) be selectively permeable. Knowledge about the exact permeation rates istherefore essential.

Fuel Cell Configuration

• Tires: Air pressure in tires should decrease as slowly as possible. Agood tire is one that allows the least amount of gas to escape.Permeation will occur over time with the tires, so it is best to knowthe permeability of the material that will make up the tire with thedesired gas to make the most efficient tires.

•• Insulating material: Water vapour permeation of insulating materialis important as well as for submarine cables to protect the conductorfrom corrosion.

• Fuel cells: Automobiles are equipped with Polymer ElectrolyteMembrane (PEM) fuel cells to convert hydrogen fuel and oxygenfound in the atmosphere to produce electricity. However, these cellsonly produce around 1.16 volts of electricity. In order to power avehicle, multiple cells are arranged into a stack. A stack's poweroutput depends on both the number and the size of the individual fuel cells.

•• Thermoplastic and Thermosetting Piping: Pipes intended to transport water under high pressure can be consideredas failed when there is a detectable permeation of water through the pipe wall to the outer surface of the pipe.

•• Medical Uses: Permeation can also be seen in the medical field in drug delivery. Drug patches made up ofpolymer material contain a chemical reservoir that is loaded beyond its solubility, and then transferred to the bodythrough contact. In order for the chemical to release itself into the body, it must permeate and diffuse through thepolymer membrane, according to the concentration gradient. Due to the over solubility of the reservoir, transportof the drug follows the burst and lag mechanism. There is a high transfer rate of the drug when the patch makescontact with the skin, but as time increases a concentration gradient is established, meaning delivery of the drugsettles to a constant rate. This is crucial in drug delivery and is used in cases such as the Ocusert System.

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Permeation 3

Permeation measurement

Permeation measurement with sweep gas

The permeation of films and membranes can be measured with any gasor liquid. One method uses a central module which is separated by thetest film: the testing gas is fed on the one side of the cell and thepermeated gas is carried to the detector by a sweep gas. The diagramon the right shows a testing cell for films, normally made from metalslike stainless steel. The photo shows a testing cell for pipes made fromglass, similar to a Liebig condenser. The testing medium (liquid or gas)is situated in the inner white pipe and the permeate is collected in thespace between the pipe and the glass wall. It is transported by a sweepgas (connected to the upper and lower joint) to an analysing device.

Permeation can also be measured through intermittent contact. This method involves taking a sample of the testchemical and placing it on the surface of the material whose permeability is being observed while adding orremoving specific amounts of the test chemical. After a known amount of time, the material is analyzed to find theconcentration of the test chemical present throughout its structure. Along with the amount of time the chemical wason the material and the analysis of the test material, one can determine the cumulative permeation of the testchemical.The following table gives examples of the calculated permeability coefficient of certain gases through a siliconemembrane.

Gas Name Formula Silicone Permeability Coefficient (Barrer)*

Oxygen 600

Hydrogen 650

Carbon Dioxide 3250

Methanol 13900

Water 36000

•• 1 Barrer = 10-10 cm3 (STP)· cm /cm2 · s · cm-HgUnless otherwise noted, permeabilities are measured and reported at 25C (RTP) and not (STP) From: THINSILICONE MEMBRANES-THEIR PERMEATION PROPERTIES AND SOME APPLICATIONS Annals of theNew York Academy of Sciences, vol. 146, issue 1 Materials in, pp. 119–137 W. L. Robb

Approximation using Fick's First lawThe flux or flow of mass of the permeate through the solid can be modeled by Fick's first law.

This equation can be modified to a very simple forumula that can be used in basic problems to approximatepermeation through a membrane.

where• is the "diffusion flux"• is the diffusion coefficient or mass diffusivity• is the concentration of the permeate

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Permeation 4

• is the thickness of the membraneWe can introduce into this equation, which represents the sorption equilibrium parameter, which is the constantof proportionality between pressure ( ) and . This relationship can be represented as .

The diffusion coefficient can be combined with the sorption equilibrium parameter to get the final form of theequation, where is the permeability of the membrane. The relationship being

Solubility of a gas in a metalIn practical applications when looking at gases permeating metals, there is a way to relate gas pressure toconcentration. Many gases exist as diatomic molecules when in the gaseous phase, but when permeating metals theyexist in their singular ionic form. Sieverts' law states that the solubility of a gas, in the form of a diatomic molecule,in metal is proportional to the square root of the partial pressure of the gas.The flux can be approximated in this case by the equation:

We can introduce into this equation, which represents the reaction equilibrium constant. From the relationship.

The diffusion coefficient can be combined with the reaction equilibrium constant to get the final form of theequation, where is the permeability of the membrane. The relationship being

External links• Diffusion Coefficient of Gas, Liquid & Vapour in Polymers [1]

Further reading• Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6•• Massey,L K, "Permeability Properties of Plastics and Elastomers", 2003, Andrew Publishing, ISBN

978-1-884207-97-6•• ASTM F1249 Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting

Using a Modulated Infrared Sensor•• ASTM E398 Standard Test Method for Water Vapor Transmission Rate of Sheet Materials Using Dynamic

Relative Humidity Measurement•• ASTM F2298 Standard Test Methods for Water Vapor Diffusion Resistance and Air Flow Resistance of Clothing

Materials Using the Dynamic Moisture Permeation Cell•• F2622 Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using

Various Sensors•• F1383: Standard Test Method for Permeation of Liquids and Gases through Protective Clothing Materials under

Conditions of Intermittent Contact.

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Permeation 5

• THIN SILICONE MEMBRANES-THEIR PERMEATION PROPERTIES AND SOME APPLICATIONS Annalsof the New York Academy of Sciences, vol. 146, issue 1 Materials in, pp. 119–137 W. L. Robb

•• Pharmaceutical Systems for Drug Delivery, David Jones; Chien YW. 2nd ed. New York: Marcel Dekker, Inc;1992. Novel drug delivery systems.

• O.V. Malykh, A.Yu. Golub, V.V. Teplyakov, Polymeric membrane materials: New aspects of empiricalapproaches to prediction of gas permeability parameters in relation to permanent gases, linear lower hydrocarbonsand some toxic gases, Advances in Colloid and Interface Science, Volume 164, Issues 1–2, 11 May 2011, Pages89–99, ISSN 0001-8686, 10.1016/j.cis.2010.10.004.

(http:/ / www. sciencedirect. com/ science/ article/ pii/ S0001868610001910) Keywords: Prediction ofgas/hydrocarbons membrane separation; Toxic gas permeability; Structure/diffusivity relations

References[1] http:/ / www. composite-agency. com/ messages/ 3875. html

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Article Sources and Contributors 6

Article Sources and ContributorsPermeation  Source: http://en.wikipedia.org/w/index.php?oldid=590506129  Contributors: Arjayay, Bearcat, Berland, Braincricket, Dthomsen8, Femtophysiker, Gavia immer, Gerben49,GoingBatty, Heron, Jeepday, Jenks24, Jimp, John gordon 54, Jtslm, Kate Stuart, MatSciWiki, Mwtoews, Neelix, Opsoelder, Pbsouthwood, Pkgx, Rlsheehan, Scheinwerfermann, SmokeyJoe,Stainarr, Steven J. Anderson, Thiseye, ZerwasC, Ziggurat, 28 anonymous edits

Image Sources, Licenses and ContributorsFile:Fuel cell still.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Fuel_cell_still.gif  License: Public Domain  Contributors: -image:Permeation sweep gas.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Permeation_sweep_gas.gif  License: Creative Commons Attribution-Sharealike 2.5  Contributors:Opsölder

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