Molecular Simulations of Solute Transport in Polymer Melts
K Zhang and SK Kumar, ACS MACRO LETTERS, 6, 864-868 (2017).
Polymer membranes are typically used to separate gas mixtures on the basis of molecular size differences ("sieving"). The gas purity is known to be inversely proportional to the membrane flux, and the slope of this plot in glassy polymers is empirically found to be determined by the sizes of the gas molecules being separated, lambda = (d(B)/d(A))(2) - 1. Despite potential mechanistic differences, the separation performance of rubbery polymers is often discussed in the same framework as their glassy counterparts. Here we perform molecular dynamics simulations of spherical solutes in coarse-grained high-density, high temperature polymer melts to gain a molecular understanding of their transport and separation behavior. We find that the diffusion coefficient follows an exponential law D similar to e(-ad). Since this dependence results in lambda = d(B)/d(A) - 1, these findings do not provide a direct understanding of the experimentally deduced slope of the Robeson plot.
Return to Publications page