Molecular simulations of gas transport in hydrogenated nitrile butadiene rubber

Diffusion and sorption of five gases (H2, N2, O2, CO2, CH4) in hydrogenated nitrile butadiene rubber (HNBR) have been investigated via molecular dynamics and grand canonical Monte Carlo (GCMC) simulations. According to the simulation results, the diffusion coefficients of gas molecules in HNBR decrease in the penetrant order D(H2) > D(O2) > D(N2) > D(CH4) > D(CO2), which are well correlated with effective penetrant diameter except for CO2. The decrease of D(CO2) is due to the interaction between CO2 and HNBR and the linear shape of CO2. The sorption isotherms for H2, N2, O2 and CH4 in HNBR fit the Henry model, while that of CO2 matches well with dual sorption model. Solubility coefficients of gas molecules in HNBR decrease in the sequence S(CO2) > S(O2) > S(CH4) > S(N2) > S(H2), which are associated with the effective Lennard-Jones interaction constant (e/k) apart from CH4. The weak interaction between CH4 with HNBR decreases S(CH4), while the high compressibility and strong interaction between CO2 with HNBR improve S(CO2). The permeability calculated using diffusion and solubility coefficients decrease in the order P(H2) > P(CO2) > P(O2) > P(CH4) > P(N2). The high permeabilities of H2 and CO2 are mainly resulted from the high diffusivity and solubility, respectively.