posted on 2020-02-07, 14:06authored byYafan Yang, Arun Kumar Narayanan Nair, Shuyu Sun
Molecular simulations were carried out to understand the structural
features and the sorption and diffusion behavior of methane and carbon
dioxide in amorphous poly(alkyl acrylates) in the temperature range
of 300–600 K. The hybrid Monte Carlo/molecular dynamics approach
was employed to address the effects of polymer swelling and framework
flexibility on the gas sorption. Simulations show that the glass-transition
temperature decreases with the side-chain length of poly(alkyl acrylate),
consistent with experiments. This is due to the fact that the shielding
of the polar ester groups increases with the side-chain length. The
simulated sorption isotherms for methane and carbon dioxide were in
agreement with the experimental data. The polymer swelling becomes
more pronounced, especially in the case of sorption of carbon dioxide.
A significant swelling occurs, possibly because of the greater interaction
between carbon dioxide and the polar ester groups in the polymers.
The uptake of methane and carbon dioxide by poly(alkyl acrylates)
generally increases with the side-chain length. Our simulations confirm
the experimental findings that the diffusion coefficients of methane
and carbon dioxide in poly(alkyl acrylates) increase with the side-chain
length. Interestingly, the activation energies of gas diffusion decrease
with the side-chain length. The diffusion coefficients of the penetrants
have an exponential relationship with the void fraction, which is
in agreement with the free volume theory.