Transport diffusion of light gases in polyethylene using atomistic simulations

Dutta, Ravi C. and Bhatia, Suresh K. (2017) Transport diffusion of light gases in polyethylene using atomistic simulations. Langmuir, 33 4: 936-946. doi:10.1021/acs.langmuir.6b04037


Author Dutta, Ravi C.
Bhatia, Suresh K.
Title Transport diffusion of light gases in polyethylene using atomistic simulations
Journal name Langmuir   Check publisher's open access policy
ISSN 1520-5827
0743-7463
Publication date 2017-01-31
Year available 2016
Sub-type Article (original research)
DOI 10.1021/acs.langmuir.6b04037
Open Access Status Not yet assessed
Volume 33
Issue 4
Start page 936
End page 946
Total pages 11
Place of publication Washington, DC, United States
Publisher American Chemical Society
Language eng
Subject 2500 Materials Science
3104 Condensed Matter Physics
3110 Surfaces and Interfaces
1607 Spectroscopy
1603 Electrochemistry
Abstract We explore the temperature dependence of the self-, corrected-, and transport-diffusivities of CO, CH, and N in a polyethylene (PE) polymer membrane through equilibrium molecular dynamics simulations. We also investigate the morphology of the polymer membrane based on the intermolecular radial distribution function, free volume, and pore size distribution analysis. The results indicate the existence of 1.5-3 Å diameter pores in the PE membrane, and with the increase in the temperature, the polymer swells linearly with changing slope at 450 K in the absence of gas and exponentially in the presence of gas. The gas adsorption isotherms extracted via a two-step methodology, considering the dynamics and structural transitions in the polymer matrix upon gas adsorption, were fitted using a "two-mode sorption" model. Our results suggest that CO adsorbs strongly, whereas N shows weak adsorption in PE. The results demonstrate that CO is more soluble, whereas N is least soluble. Further, it is found that an increase in the temperature negatively impacts the solubility of CO and CH but positively for N; this reverse solubility behavior is due to increased availability of pores accessible to N, which are kinetically closed at the lowest temperatures. The reported self-diffusivities of the gases from our simulations are on the order of 10 cm/s, consistent with the experimental evidence, whereas transport-diffusivities are 2 orders of magnitude higher than self-diffusivities. Furthermore, the temperature dependence of the self-diffusivity follows Arrhenius behavior, whereas the transport-diffusivity follows non-Arrhenius behavior having different activation energies in low and high temperature regions. Also, it is seen that loading has little effect on the self- and corrected-diffusion coefficients of all gases in the PE membrane. (Figure Presented).
Formatted abstract
We explore the temperature dependence of the self-, corrected-, and transport-diffusivities of CO2, CH4, and N2 in a polyethylene (PE) polymer membrane through equilibrium molecular dynamics simulations. We also investigate the morphology of the polymer membrane based on the intermolecular radial distribution function, free volume, and pore size distribution analysis. The results indicate the existence of 1.5-3 Å diameter pores in the PE membrane, and with the increase in the temperature, the polymer swells linearly with changing slope at 450 K in the absence of gas and exponentially in the presence of gas. The gas adsorption isotherms extracted via a two-step methodology, considering the dynamics and structural transitions in the polymer matrix upon gas adsorption, were fitted using a "two-mode sorption" model. Our results suggest that CO2 adsorbs strongly, whereas N2 shows weak adsorption in PE. The results demonstrate that CO2 is more soluble, whereas N2 is least soluble. Further, it is found that an increase in the temperature negatively impacts the solubility of CO2 and CH4 but positively for N2; this reverse solubility behavior is due to increased availability of pores accessible to N2, which are kinetically closed at the lowest temperatures. The reported self-diffusivities of the gases from our simulations are on the order of 10-6 cm2/s, consistent with the experimental evidence, whereas transport-diffusivities are 2 orders of magnitude higher than self-diffusivities. Furthermore, the temperature dependence of the self-diffusivity follows Arrhenius behavior, whereas the transport-diffusivity follows non-Arrhenius behavior having different activation energies in low and high temperature regions. Also, it is seen that loading has little effect on the self- and corrected-diffusion coefficients of all gases in the PE membrane.
Keyword Chemistry, Multidisciplinary
Chemistry, Physical
Materials Science, Multidisciplinary
Chemistry
Materials Science
Q-Index Code C1
Q-Index Status Provisional Code
Grant ID DP150101996
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
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