Document Type : Research Article
Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan, Zahedan, I.R. IRAN
In this research, the diffusion coefficients of hydrogen and oxygen gases and the permeability coefficient of hydrogen gas in polystyrene are studied by using molecular dynamics simulations. The diffusion coefficients of hydrogen and oxygen gases over a wide range of temperatures 300-500 K are calculated from center-of-mass mean-square displacements of gas in polystyrene. The results of this research indicated that the calculated diffusion coefficients are in good agreement with the experimental data and the results of previous simulation studies. Also, the diffusion regime at higher temperatures sets in a shorter time compared to a lower temperature. The results for the temperature dependence of the diffusion coefficient indicate that a linear correlation is valid between ln(D) and 1/T over the whole studied temperature range. We calculated the diffusion activation energy from the temperature dependence of the diffusion coefficient. Also, the calculated permeability coefficients are in better agreement with experiment data compared to previous simulation studies. The radial distribution function in different temperatures between penetrant gas and different parts of the polymer chain indicates that gas molecules are closer to phenyl groups compared to aliphatic groups. Our results show that hydrogen molecules which have smaller sizes compared to oxygen molecules, are closer to the polymer chain but they have weaker interaction with the polymer chain.