2025 AIChE Annual Meeting

(164g) Chemical Structure Selectivity with Nanostructured Polymer Membranes

Authors

Ayse Asatekin, Tufts University
Kazuya Morishita, University of Texas at Austin
Venkatraghav Ganesan, The University of Texas at Austin
Membranes provide energy-efficient, scalable, and environmentally-friendly separation processes to chemical manufacturing. However, current filtration membranes cannot separate similarly sized and charged solutes, including small organic molecules. Biological pores show that chemical-structure based separations are feasible with properly confined pores that consist of functional groups displaying selective yet reversible interactions along the pore walls. We hypothesize that membranes that feature functional nanopores, which mimic these biological structures, can also exhibit selectivity between dissolved organic molecules, mediated by pore-solute interactions. We aim to create such functional nanostructures using self-assembling polymers, which enables the use of scalable manufacturing methods. Our previous work has shown that Zwitterionic Amphiphilic Copolymers (ZACs), which combine hydrophobic and zwitterionic repeat units in a random/statistical copolymer, self-assemble to create disordered bicontinuous domains. The hydrophilic, zwitterionic domains act as a network of water-permeable “nanochannels”, ~1-1.5 nm in effective diameter, lined with the zwitterionic groups that form them. Thin film composite (TFC) membranes with ZAC selective layers exhibit size cut-offs similar to these domain sizes, with ability to selectively retain larger organic molecules. The effective channel size can be tuned by cross-linking if the hydrophobic monomers include reactive groups (e.g. double bonds for thiol-ene crosslinking). Work with ZAC membranes featuring the commercial zwitterion sulfobetaine methacrylate (SBMA) showed excellent anion-anion separations when crosslinked to an effective pore size of ~0.9 nm. In this study, we aim to develop ZAC TFC membranes that can separate dissolved organic molecules based on the presence of a specific functional group (e.g. aromatic ring). For this purpose, we identified and synthesized a zwitterionic monomer with an aromatic ring that can potentially interact preferentially with aromatic molecules through pi-pi interactions. This monomer, sulfobetaine-methyl styrene (SBMS), was copolymerized with a hydrophobic monomer to form a novel ZAC, which was then cast as a thin-film composite membrane on top of a microporous support. These ZACs show effective pore sizes around 1.5 nm. Preliminary results suggest that these membranes exhibit some selectivity between larger organic molecules with and without aromatic groups (e.g. trisaccharides and aromatically labeled disaccharides), close to 1.5. Differences in the strength of interaction between SBMS lining the pores and the permeating molecules are corroborated by molecular dynamics analysis. These findings hint at a larger chemical-structure-based permeation selectivity that can be achieved with confined nanopores consisting of tunable functional groups on the pore walls.