DIFFUSION-RELAXATION COUPLING IN POLYMERS WHICH SHOW 2-STAGE SORPTION PHENOMENA

The diffusion behaviour of swollen polymer films in interval sorption experiments cannot be explained satisfactorily by the available models for diffusion into polymeric materials, and compels us to accept that the state of the swollen polymer should be characterized not only by the state variables such as temperature and pressure but also by a 'degree of swelling'. The concept of activity parameter as an internal state variable is introduced as an yardstick for the degree of swelling and the rate of evolution of this has been related directly to the concept of relaxation time. Assuming a simple empirical constitutive rate equation for the physical process involved, asymptotic as well as the complete solution of the proposed mathematical model are developed and the results agree well with the available experimental data on two-stage sorption. © 1979.