Membranes that separate small molecules of similar size in the liquid phase based on their chemical properties would transform chemical manufacturing. Here, we aim to prepare synthetic polymer membranes that mimic key features of biological pores such as ion channels and porins: Constricted nanopores that confine permeation, lined with functional groups that interact with the target during passage. We first focused on membranes capable of charge-based separation through electrostatic interactions. To build these nanostructured layers using scalable techniques, we deposited packed arrays of polymer micelles whose coronas exhibit carboxylic acid groups, formed by a random copolymer of trifluoroethyl methacrylate (TFEMA) and methacrylic acid (MAA) in methanol, onto a porous support membrane. When these micelles are coated onto the surface of a porous support membrane whose pores are smaller than the micelles and then immersed into water, a selective layer of micelles packed together is formed. The gaps between the micelles act as nanochannels functionalized with carboxylic acid groups. The membrane showed charge-based selectivity between organic molecules, effectively rejecting negatively charged solutes while allowing the passage of neutral solutes in two-solute separation tests. Interestingly, selectivity was enhanced when a mixture of solutes was used, due to competition between solutes to enter the very narrow pores. We then functionalized the carboxyl groups with phenol moieties that can preferentially interact with aromatic groups through pi-pi interactions. This has enabled us to impart significant diffusion selectivity of ~10 between two hormones of identical size and charge, differentiated by the presence of an aromatic ring. We believe these approaches will eventually lead to novel membranes that can separate molecules of similar size but different chemical structure.

Membranes for charge- and aromaticity-based separation of small molecules

2019 Spring National Meeting

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