(288a) Membranes with Chemical Structure-Based Selectivity from the Assembly of Functionalizable Random Copolymer Micelles

Regulating permeation through materials is crucial for many applications including selective membranes, controlled drug delivery, and packaging. An ideal membrane material would pass the desired molecules with little resistance (high permeability) while preventing the passage of all else (high selectivity). However, synthetic materials today cannot meet this challenge. There are no commercially available membranes that can separate small molecules of similar size in the liquid phase based on their chemical properties. In this study, we aim to prepare synthetic polymer membranes that mimic two key features of biological pores such as ion channels and porins: Constricted pores only 1-5 nm in diameter, lined with functional groups lining the pore that interact with the target during passage. The nanostructure constricts flow and confines all components passing through, forcing them to interact with the chemically functional walls. As an initial system, we 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 onto a porous support membrane. Random copolymers that combine highly hydrophobic fluorinated repeat units of trifluoroethyl methacrylate (TFEMA) with ionizable repeat units of methacrylic acid (MAA) form micelles and vesicles in methanol. 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, efficiently rejecting negatively charged solutes while allowing the passage of neutral solutes in two-solute separation tests. Furthermore, the carboxyl groups can be post-functionalized to alter the selectivity of the membrane for desired separations. Such functionalization has enabled us to impart significant diffusion selectivity of about 10 between two solutes of identical size and charge, differentiated by minor chemical features. This demonstrates the potential of using polymer self-assembly and functionality to design membranes that mimic biological pores while maintaining scalable manufacturing methods. We believe these approaches will eventually lead to novel membranes that can separate molecules of similar size but different chemical structure.