Molecular dynamics characterization of structural properties of <i>ɛ</i>-phase syndiotactic polystyrene

Abstract

The structure of ɛ-phase syndiotactic polystyrene was investigated, based on geometrical analysis and diffusion paths of light gases, to determine the shape and size of its channels (porous). Pore size distribution and empty volume fraction were determined using PoreBlazer v4.0. Diffusion trajectory paths DA of gases such as H2, D2, He, CO2, N2, CH4, C2H4, and C2H6 were calculated by molecular dynamics at temperatures T = 298, 313, 333, and 353 K; additionally, diffusion coefficients were also determined. For the smaller gases (H2, D2, and He), quantum corrections were also considered using a Wigner–Kirkwood approximation applied to the Lennard-Jones effective potential. It was observed that in some cases, gases such as He, H2, D2, and CO2 could percolate across the channels in the crystal at T = 353 K. These gases also showed the highest diffusion coefficients along the Z axis. Interestingly, CO2, which was the heaviest molecule of all gases in this study and showed the lowest diffusion coefficient, could also percolate through the structure.