In Silico Determination of Gas Permeabilities by Non-Equilibrium Molecular Dynamics: CO2 and He through PIM-1

Hendrik Frentrup; Kyle E Hart; Coray M Colina; Erich A Müller

doi:10.3390/membranes5010099

In Silico Determination of Gas Permeabilities by Non-Equilibrium Molecular Dynamics: CO2 and He through PIM-1

Membranes (Basel). 2015 Mar 10;5(1):99-119. doi: 10.3390/membranes5010099.

Authors

Hendrik Frentrup¹, Kyle E Hart², Coray M Colina³, Erich A Müller⁴

Affiliations

¹ Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK. hendrik.frentrup10@imperial.ac.uk.
² Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA. keh243@psu.edu.
³ Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA. colina@matse.psu.edu.
⁴ Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK. e.muller@imperial.ac.uk.

Abstract

We study the permeation dynamics of helium and carbon dioxide through an atomistically detailed model of a polymer of intrinsic microporosity, PIM-1, via non-equilibrium molecular dynamics (NEMD) simulations. This work presents the first explicit molecular modeling of gas permeation through a high free-volume polymer sample, and it demonstrates how permeability and solubility can be obtained coherently from a single simulation. Solubilities in particular can be obtained to a very high degree of confidence and within experimental inaccuracies. Furthermore, the simulations make it possible to obtain very specific information on the diffusion dynamics of penetrant molecules and yield detailed maps of gas occupancy, which are akin to a digital tomographic scan of the polymer network. In addition to determining permeability and solubility directly from NEMD simulations, the results shed light on the permeation mechanism of the penetrant gases, suggesting that the relative openness of the microporous topology promotes the anomalous diffusion of penetrant gases, which entails a deviation from the pore hopping mechanism usually observed in gas diffusion in polymers.