Characterization of permeability and sorption in Matrimid/C₆₀ mixed matrix membranes

Mixed matrix membrane is a highly potential material that may possibly overcome the challenges faced by the membrane technology today. We explored the gas separation performance of a modified Matrimid/C₆₀ mixed matrix membranes. The membranes were prepared by physically blending a series of benzylamine-modified fullerene, C₆₀ with pure Matrimid 5218. The bulk Matrimid and the dispersed benzylamine-modified fullerene molecules show strong interfacial interactions as reflected by a significant increase in the T_g of the film with C₆₀ loading. Gas permeabilities of He, O₂, N₂, CH₄, and CO₂ show a monotonous decrease with increasing benzylamine-modified C₆₀ content. The percentage of permeation reduction at 10wt.% benzylamine-modified C₆₀ loading is 32% for He (kinetic diameter of 2.6Å), while 41.7 and 41.5%, respectively, for the O₂ (3.46Å) and N₂ (3.64Å) gas pair, 45.2 and 47.0%, respectively, for CH₄ (3.8Å) and CO₂ (3.3Å) gas pair. The decrease of the gas permeability with increasing C₆₀ compositions is found to be mainly due to the decrease in the gas diffusivity. The presence of the benzylamine-modified C₆₀ seems to serve as impenetrable volumes and rigidifying elements within the polymer matrix. Therefore, the diffusivity of larger penetrants is reduced to a greater extent than the smaller penetrants and results in the increase of He/N₂ selectivity. This is also supported by the sorption data, which reveals that the Langmuir sorption capacity decreases with increasing C₆₀ loading. The increase in the glass transition temperature and the measured density indicate that the presence of the chemically modified C₆₀ molecules have rigidified the polymer and pulled the matrix together.