Block copolymers (BCPs) are useful materials because of their propensity to self-assemble into different morphologies, such as lamellae, cylinders, and gyroids. BCPs with the cylinder or gyroid morphology can be used to make membranes with uniform pore sizes and well-defined pore structure. The cylinder morphology has been widely studied for membrane applications and cylinder-forming BCPs can be readily synthesized. However, it is challenging to align the cylindrical channels perpendicular to the top surface and to make them extend continuously through the entire thickness of a BCP film. The gyroid-forming BCP, on the other hand, is very unique. Without any alignment control, it can form continuous channels extending through the entire BCP film. Therefore, it is of interest to exploit the gyroid structure made from BCPs for membrane applications. However, the gyroid morphology exists only over a very narrow range of volume fractions and therefore, reproducible synthesis of such materials is challenging. In this work, diblock copolymers comprising substituted polystyrene as the nonpolar block and polylactide as the polar block were explored. The combination of living anionic polymerization and organocatalytic ring-opening polymerization (ROP) provides precise control over the composition and the molecular weight of BCPs. The substituted polystyrene forms the matrix while the polylactide can be etched away to form continuous pore channels embedded inside the matrix. In this work, the porous gyroid film was first made on a glass or silicon substrate and the gyroid structure was characterized by Scanning Electron Microscopy (SEM) and Small Angle X-ray Scattering (SAXS). Unfortunately, the porous gyroid film is not mechanically stable and cannot be use as a free-standing membrane. Hence, the porous gyroid film was integrated on top of a porous polyethersulfone (PES) supporting membrane to make a thin-film composite membrane, which is mechanically stable. This gyroid thin-film composite membrane was tested for gas permeation and water purification processes.

Gyroid thin-film composite membranes for ultrafiltration processes

2019 Fall National Meeting

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