The rate of solvent diffusion in amorphous polymers

The present work is a contribution to our understanding of one aspect of the diffusion process, the diffusion rate. It attempts to show that all diffusion theories must satisfy the following:

1) the rate of diffusion at the initial stages of the process must be finite

2) the rate of diffusion must have square root time dependence at longer diffusion distances.

Deviations of experimental data from these rules usually result from experimental inaccuracies. Whereas Fickian approach satisfies the second but not the first rule and Case II sorption the opposite, their combination satisfies neither. Two alternative explanations, which provide a very good correlation with the experimental data, are suggested: Limited diffusion rate and sorption kinetics.