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 Tg 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 10 wt.% benzylamine-modified C60 loading is 32% for He (kinetic diameter of 2.6 Å), while 41.7 and 41.5%, respectively, for the O2 (3.46 Å) and N2 (3.64 Å) gas pair, 45.2 and 47.0%, respectively, for CH4 (3.8 Å) and CO2 (3.3 Å) 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.