Permeation
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Permeation
General
The driving force behind this process is a pressure or concentration gradient within the single solid. Without the influence of external factors, the substance always moves in the direction of lower concentration or pressure. Permeation takes place in several steps:
- Adsorption: The substance accumulates on the surface. This can occur from the gas phase or through direct contact with the liquid or solid substance.
- Absorption: The substance is absorbed.
- Diffusion: This is where the penetration of the material at the molecular level begins. The substance penetrates the solid through pores or molecular interstices.
- Desorption: After the molecules have penetrated the solid, they diffuse away from the surface again.
Examples of the importance of permeation
- Working with protective gloves in laboratories or production facilities.
- Food packaging should either be completely airtight (sausages, cheese, drinks) or selectively permeable (e.g. for oxygen in fruit).
Performing permeation measurements
Films and membranes are tested for permeability using any gases or liquids. Special measuring cells have been developed for this purpose. These cells are usually made of metal, such as stainless steel. When testing gases, a test gas is passed through the measuring cell and the amount remaining after passing through is measured by a detector in terms of concentration.
Analogous to the permeation measurement for gases, the so-called water value is determined in membrane technology. It is used to characterise the performance of a liquid filtration unit and is expressed in l/m2 • h • bar.
See also
Weblinks
- Wikipedia – The free Encyclopedia: Permeation (https://en.wikipedia.org/wiki/Permeation) (last accessed February 11, 2026)