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

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.

Concentration gradient driven molecular dynamics: a new method for simulations of membrane permeation and separation

“…The same authors extended their method to investigate single gas permeation of CO 2 and He through a PIM-1 polymer membrane. 26 Even though their methodology allows the circulation of fluid molecules between the permeate and feed sides to ensure a continuous simulation, it does not provide any control over the density of fluids at the inlet and outlet of the membrane. To address the shortcomings of previous methods Ható et al 15 proposed a methodology which was essentially a combination of the method of Frentrup et al 25 and of the DCV-GCMD method of Heffelfinger et al , 11 thus again requiring the coupling of MC and MD algorithms.…”

Dynamics of water and solute transport in polymeric reverse osmosis membranes via molecular dynamics simulations

“…EMD has been used to examine transport behaviors of water molecules through carbon nanotubes [16,17], while NEMD has been used to demonstrate the potential use of a zeolitic metal-organic framework (MOF) for water desalination [18]. In addition, NEMD has been used to study gas permeation through membranes [19,20], although we note that gas permeation differs from reverse osmosis in terms of its driving force. The driving force for gas separation mainly results from partial pressure differences, essentially differences in gas concentrations, while the driving force for reverse osmosis comes from the hydraulic pressure difference across the membrane [8,21,22].…”

Physical property and gas transport studies of ultrathin polysulfone membrane from 298.15 to 328.15 K and 2 to 50 bar: atomistic molecular simulation and empirical modelling

“…Besides, limited study has been conducted to incorporate gas molecules within the constructed ultrathin lms to elucidate gas transport properties upon connement. 20,21 Similarly, the construction of ultrathin lm at xed dimensions has restrained the elucidation of connement towards thicknessdependent gas transport properties. 20,21 Frentrup et al (2012) developed a novel non-equilibrium molecular dynamics (NEMD) simulation along the thickness of a polymer slice and demonstrate how permeability and solubility can be reasoned from a single simulation.…”

“…20,21 Similarly, the construction of ultrathin lm at xed dimensions has restrained the elucidation of connement towards thicknessdependent gas transport properties. 20,21 Frentrup et al (2012) developed a novel non-equilibrium molecular dynamics (NEMD) simulation along the thickness of a polymer slice and demonstrate how permeability and solubility can be reasoned from a single simulation. 20 Tong et al (2016) simulated 2dimensional (2-D) Covalent Organic Framework (COF) ultrathin membranes through computational study in layers to explore the gas separation of such structures.…”