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Abstract
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Molecular dynamics simulations are performed to determine the solubility and diffusion coefficient
of carbon dioxide and nitrogen in poly(methyl methacrylate) (PMMA). The solubilities of CO2 in
the polymer are calculated employing our grand canonical ensemble simulation method, fixing the
target excess chemical potential of CO2 in the polymer and varying the number of CO2 molecules
in the polymer matrix till establishing equilibrium. It is shown that the calculated sorption isotherms
of CO2 in PMMA, employing this method well agrees with experiment. Our results on the diffusion
coefficients of CO2 and N2 in PMMA are shown to obey a common hopping mechanism. It is shown
that the higher solubility of CO2 than that of N2 is a consequence of more attractive interactions
between the carbonyl group of polymer and the sorbent. While the residence time of CO2 beside
the carbonyl group of polymer is about three times higher than that of N2, the diffusion coefficient
of CO2 in PMMA is higher than that of N2. The higher diffusion coefficient of CO2, compared to
N2, in PMMA is shown to be due to the higher (?3 times) swelling of polymer upon CO2 uptake.
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