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Coarse-Grained Molecular Dynamics Simulation of Activated Penetrant Transport in Glassy Polymers

Abstract

Membrane separations of gas mixtures strive to maximize the permeability of a desired species while keeping out undesired ones. Permeability vs. selectivity data from many polymer membranes for a given gas pair with diameters $d_A$ and $d_B$ are typically collected in a ``Robeson plot'', which are bounded from above by a line with a slope $\lambda=(d_B/d_A)^2-1$. A microscopic understanding of this relationship, especially $\lambda$, is still missing. We perform molecular dynamics simulations of penetrant diffusion using three different coarse-grained polymer models over a wide range of penetrant sizes, temperatures, and monomer densities. The empirically relevant $\lambda=(d_B/d_A)^2-1$ is only found for polymers that are either supercooled liquids with caged segmental dynamics or glasses and when the penetrant size is approximately half the Kuhn length of the chains, for which the penetrant diffusion is an activated process.

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Publication details

The article was received on 26 Sep 2017, accepted on 27 Nov 2017 and first published on 27 Nov 2017


Article type: Paper
DOI: 10.1039/C7SM01941F
Citation: Soft Matter, 2017, Accepted Manuscript
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    Coarse-Grained Molecular Dynamics Simulation of Activated Penetrant Transport in Glassy Polymers

    K. Zhang, D. Meng, F. Mueller-Plathe and S. Kumar, Soft Matter, 2017, Accepted Manuscript , DOI: 10.1039/C7SM01941F

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