Case-II diffusion in polymers. I. Transient swelling
Journal
Journal of Applied Physics
Journal Volume
61
Journal Issue
11
Pages
5129-5136
Date Issued
1987
Author(s)
Abstract
The swelling of a polymer glass by sorption of a small molecule penetrant is considered in a regime characterized by so-called case-II diffusion. Attention is focused on the polymer so that the swelling process can be investigated apart from diffusion. The model of Thomas and Windle (TW) is used to predict the surface swelling as a function of exposure time. This model assumes that the swelling is driven by the osmotic pressure which relaxes to zero as the surface penetrant volume fraction φs approaches its equilibrium value φe. The rate-controlling factor of the swelling process is the viscosity of the polymer η, which decreases with increasing surface sorption according to η=η0 exp(-mφ) where η0 is the viscosity of the unswollen polymer. For large values of M=mφe, φs is very small until a time τ is reached beyond which the swelling then accelerates rapidly towards its equilibrium value. This feature is absent if M
Type
journal article