Important Factors In Permeation MeasurementSource: MOCON, Inc.
By Michelle Stevens, MOCON, Inc.
WHAT IS PERMEATION?
Graham’s Colloidal Diffusion illustrates the three-step process of permeation through a material. The first step is the sorption of the permeant into the material. Next, the permeant diffuses through the material followed by the final step where it is desorbed from the other side. This entire process is driven by a concentration difference or gradient. Molecules will permeate from the high concentration side of the material to the low concentration side. This will continue until both sides are at equal concentration levels.
Permeation measurement is generally a straight-forward concept. However, terminology surrounding permeation and its measurement is often used incorrectly. Permeation rate and transmission rate are used interchangeably but are, in fact different properties. The rate at which the permeant goes through a material of a specific area is evaluated to give the transmission rate. The units of transmission rate have the dimensions of volume of permeant per unit area per time.