Smectic Liquid Crystalline Polymer Membranes with Aligned Nanopores in an Anisotropic Scaffold

Abstract

Bottom-up methods for the fabrication of nanoporous polymer membranes have numerous advantages. However, it remains challenging to fabricate nanoporous membranes that are mechanically robust and have aligned pores, that is, with a low tortuosity. Here, a mechanically robust thin-film composite membrane was fabricated consisting of a two-dimensional (2D) porous smectic liquid crystalline polymer network inside an anisotropic, microporous polymer scaffold. The polymer scaffold allows for relatively straightforward planar alignment of the smectic liquid crystalline mixture, which consisted of a diacrylate cross-linker and a dimer forming benzoic acid-based monoacrylate. Polymerized samples displayed a smectic A (SmA) phase, which formed the eventual 2D porous channels after base treatment. The aligned 2D nanoporous membranes showed a high rejection of anionic solutes bigger than 322 g/mol. Cleaning and reusability of the system were demonstrated by intentionally fouling the porous channels with a cationic dye and subsequently cleaning the membrane with an acidic solution. After cleaning, the membrane properties were unaffected; this, combined with numerous pressurizing cycles, demonstrated reusability of the system.