DIFFUSION OF PENETRANTS IN AMORPHOUS POLYMERS - A MOLECULAR-DYNAMICS STUDY

Molecular dynamics calculations are performed that simulate the diffusion of penetrant molecules through an amorphous polymer. For the polymer and the penetrant molecules, model potentials are chosen that approximate polyethylene and methane, respectively. The simulations extend over several hundred picoseconds. The results indicate that permeation proceeds by a hopping mechanism: The penetrants dwell in voids in the polymer matrix for a considerable time and perform fast jumps between neighboring voids. A potential scaling technique based on the fact that individual jump events are activated processes is presented by which the calculation of penetrant self-diffusion coefficients is speeded up.