Permeation

[1] Permeation is modeled by equations such as Fick's laws of diffusion, and can be measured using tools such as a minipermeameter.

The process of permeation involves the diffusion of molecules, called the permeant, through a membrane or interface.

This is a very important mechanism in biology where fluids inside a blood vessel need to be regulated and controlled.

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 considered carefully in many 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.

The diagram on the right shows a testing cell for films, normally made from metals like stainless steel.

The photo shows a testing cell for pipes made from glass, similar to a Liebig condenser.

It is transported by a sweep gas (connected to the upper and lower joint) to an analysing device.

After a known amount of time, the material is analyzed to find the concentration of the test chemical present throughout its structure.

119–137 [4] The 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 formula that can be used in basic problems to approximate permeation through a membrane.

The diffusion coefficient can be combined with the sorption equilibrium parameter to get the final form of the equation, where

In practical applications when looking at gases permeating metals, there is a way to relate gas pressure to concentration.

The diffusion coefficient can be combined with the reaction equilibrium constant to get the final form of the equation, where