THE EFFECT OF MOLECULAR-SIZE ON NON-FICKIAN SORPTION IN GLASSY-POLYMERS

Rutherford backscattering spectrometry has been used to determine the concentration against depth profiles of n-iodoalkanes diffusing into a polymer glass photoresist. All the iodoalkanes smaller than iodohexane show strongly non-Fickian diffusion. After an induction time a sharp front forms, with almost no concentration gradient behind the front. Ahead of the front the concentration decreases exponentially with depth, a form predicted for Fickian diffusion ahead of a moving boundary. The polymer investigated was a commercial dry film photoresist, Riston. Its nominal chemical composition is close to that of polymethylmethacrylate.