Diffusion of Gases and Liquids in Glassy and Semi-Crystalline Polymers

Synopsis

The diffusion of small molecules in polymers above the glass transition temperature appears to be dominated by those factors which affect the Rouse segment mobility, e.g. the diffusion coefficient is strongly concentration dependent in accord with predictions of free-volume theories. The major complication arises due to dispersed homogeneities such as crystallinity. The effect of such inhomogeneities are not well described by simple two phase models. We shall review previous attempts to deal with crystallinity in rubbery polymers. While rubbery polymers respond rapidly to changes in their condition this is not the case with glassy polymers. Diffusion in such polymers is often dominated by finite rate relaxation effects which produce a whole range of anomolous behavior. We will discuss some recent attempts to describe the coupling of mass transport with relaxation behavior whose origin can be mechanical or structural.