Abstract
We propose a model for calculating a constitutive relation for the dynamics of solvent-polymer systems close to the glass transition. We do it by considering a layer of thickness ξ of a few nanometers which is submitted to an arbitrary time varying solvent activity a(t). We show then how these constitutive relations allow to explain case-II diffusion in glassy polymers and provide a physical interpretation for the parameters of the Thomas-Windle model. Regarding the process of film drying, we show that films up to 1 μm thick can be almost completely dried in an accessible experimental time, even at temperatures well below the polymer glass transition temperature. When drying a thicker film, we show that a glassy crust may appear on the free surface, as has been shown experimentally.