Submicron Films of Polymer Blends: Unlocking Microphase Separation to Enhance Membrane Gas Separation Properties

Polymers are crucial in enabling membrane technology for energy-efficient gas separation, and they are subject to the permeability-selectivity trade-off. Polymers can be incorporated with inorganic fillers to improve gas transport properties; however, the two distinctive phases often exhibit interfacial incompatibility, making it difficult to fabricate defect-free submicrometer thin-film composite (TFC) membranes. In this study, we demonstrate microphase-separated polymer blends achieving superior H₂/CO₂ separation properties by dispersing a highly permeable and nonselective polyimide (6FDA-DAM, PI) phase in a highly selective but nearly impermeable continuous polybenzimidazole (PBI) phase. The effect of the PI loading on physical and morphological properties is systematically investigated, and its influence on H₂ permeability can be satisfactorily described using the Maxwell model. Adding 40 mass% PI increases H₂ permeability by 340% from 27 to 120 Barrer while retaining H₂/CO₂ selectivity of 10 at 150 °C, surpassing Robeson's upper bound. More importantly, the blends can be fabricated into submicrometer layers in TFC membranes with microphase separation, achieving H₂ permeance 250% higher than that of PBI membranes. This work presents a versatile and scalable method to enhance the separation performance of advanced polymeric membranes through microphase blending using current manufacturing processes.