Water permeation of polymer films. IV. Teflon FEP

The evaluation of the permeation parameters of water for Teflon FEP has shown that permeation is a dual mode process: Water is initially adsorbed onto the polymer surface in a layer; because the residence time of the layer is short, little is ultimately absorbed. The diffusion process is disrupted at the onset of molecular motion, at the glass transition, due to an increase in effective tortuosity. Variations of the permeation parameters with thickness suggest a skin, of total thickness near 25 μm, whose permeation parameters differ from those of the bulk.