A study on free volume controlled diffusion in polymers

The influence of iodine sorption on the free volume of three technologically important polymers viz., Polycarbonate, Poly(ethyleneterephthalate) and Acrylonitrile Butadiene Styrene have been investigated Positron Annihilation Lifetime Spectroscopy is used for characterizing the free volume holes and sorption method is used to determine the Diffusion coefficient. The observed results indicate the filling of free volume holes by the iodine molecules and the swelling of these holes. The present study also shows that iodine acts as an inhibitor of ortho-Positronium. The iodine diffusion process in Poly(ethyleneterephthalate) and Acrylonitrile Butadiene Styrene departs from Fick's law whereas Polycarbonate obeys Fick's law of diffusion. Interestingly, the present results show that the polymers which deviate from Fick's law of diffusion also deviate from Fujita's free volume concept as far as fractional free volume and the Diffusion coefficient are concerned.