Novel compatibilized immiscible polymer blend based membranes for gas separations

In this work, an alternative pathway to improve gas separation performance was investigated by developing a novel membrane microstructure comprising high performance, immiscible polymer blends compatibilized with metal organic frameworks (MOFs) and small molecules. In chapter one, a detailed introduction to the research background is provided explaining the need and the advantages of this novel approach. In chapter two, the use of zeolitic immidazolate framework-8 (ZIF-8) in controlling phase separation and driving membrane microstructure of a high performance, immiscible 6FDA-DAM:DABA (3:2): polybenzimidazole (PBI) blend is described. The membrane microstructure was examined using a battery of imaging techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). With a small loading of ZIF-8 (5% (w/w)), the membrane morphology became stabilized as indicated by uniform and smaller domains of the dispersed phase. As the ZIF-8 loading was further increased, the dispersed domains became even smaller suggesting even better compatibility. These results were attributed to the interfacial localization of ZIF-8, that was driven by the lowering of the interfacial energy of the system as demonstrated by a theoretical calculation that depended on water contact angle measurements. In chapter three, the same approach was used but with a different high performance 6FDA-durene:PBI immiscible polymer blends along with colloidal ZIF-8. Improved gas separation performance surpassing the Robeson's upper bound for H2/CO2 separation was observed as the membrane morphology became stabilized due to the incorporation of colloidal ZIF-8. In chapter four, the use of the small molecule, 2-methylimidazole, to compatibilize 6FDA-DAM:DABA (3:2):PBI is demonstrated. This approach is further advantageous since these small molecules are thermally labile, less expensive, and can potentially form unique gas transport pathways within the membrane microstructure. To the best of our knowledge, this is the first report of the use of small molecules and MOFs to control the membrane microstructure and extensive phase separation of high performance immiscible polymer blends.;This novel approach would benefit not only gas separations but also other membrane-based separations that use polymer blends to improve performances.