Molecular simulations of gas transport in hydrogenated nitrile butadiene rubber

Diffusion and sorption of five gases (H-2, N-2, O-2, 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(H-2) > D(O-2) > D(N-2) > 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 CO(2)and HNBR and the linear shape of CO2. The sorption isotherms for H-2, N-2, O(2)and CH(4)in HNBR fit the Henry model, while that of CO(2)matches well with dual sorption model. Solubility coefficients of gas molecules in HNBR decrease in the sequence S(CO2) > S(O-2) > S(CH4) > S(N-2) > S(H-2), which are associated with the effective Lennard-Jones interaction constant (epsilon/k) apart from CH4. The weak interaction between CH(4)with HNBR decreases S(CH4), while the high compressibility and strong interaction between CO(2)with HNBR improve S(CO2). The permeability calculated using diffusion and solubility coefficients decrease in the order P(H-2) > P(CO2) > P(O-2) > P(CH4) > P(N-2). The high permeabilities of H(2)and CO(2)are mainly resulted from the high diffusivity and solubility, respectively.