Abstract:

Diffusion of molecules with molecular weights ranging from 32 to 339 in amorphous polyethylene terephthalate(PET) was examined by using molecular dynamics simulation.The diffusion coefficients were calculated based on Einstein relation and the influence of simulation time and density on diffusion coefficients was discussed.The results showed that for a higher temperature a shorter simulation time was needed in order that the linear area in mean square displacement (MSD) curves could be observed while for a lower temperature a longer simulation time was needed.Diffusion coefficients decreased with increasing density of the polymer and a higher density required a longer simulation time.Comparison of the calculated diffusion coefficients with experimental values found in the literature indicated that the calculated and experimental values were in the same order of magnitude.It suggested that the polymer model was acceptable and could describe correctly the diffusion process of small molecules in PET.This work can provide an approximate method of calculating diffusion coefficient, which is the key parameter in the migration model.