The chemical action involving the movement of chemicals, on a molecular level, through intact materials best defines:

• A. Permeation
• B. Penetration
• C. Degradation
• D. Sorption

Answer: (A)

Permeation is the movement of a chemical through an intact barrier at the molecular level. It starts when the chemical is absorbed into the barrier’s surface, diffuses through the material, and desorbs on the far side, all while the barrier remains intact. This matters because protection can be breached even without any visible damage, unlike penetration, which involves a hole or opening. Sorption refers to the chemical being taken up by the barrier but not necessarily passing through, and degradation means the chemical is chemically attacking and breaking down the barrier itself. Understanding permeation helps explain why barrier materials have breakthrough times and permeation rates that determine how long protection lasts.