The state-of-the-art membranes for desalination are comprised of a thin film composite geometry where the permselective layer is a thin but highly crosslinked, interfacially polymerized polyamide. The rapid polymerization rate and reaction conditions produce extremely thin films with rough surface structures and chemical heterogeneity. Here, we conducted advanced measurements of composition, morphology, and dynamics of this interfacially polymerized polyamide layer, which enabled us to establish robust relationships between the chemical structure, water/ion transport, and water filtration performance of these membranes. Specifically, we used solid-state nuclear magnetic resonance (NMR) spectroscopy to establish the chemical composition of a series of polyamide membranes with varying monomer compositions, allowing acid:amine monomer ratios to be determined. We also employed quasielastic neutron scattering (QENS) to probe the dynamics of the polymer membrane as well as the local water motions within the membranes. Intriguingly, the observed local- and global diffusion of water inside the membrane are quite different. Finally, structural characterization of these samples via grazing incidence wide angle x-ray scattering (GI-WAXS) provided insight into the local packing efficiency of these membranes, and we correlated the packing efficiency to the compositional and membrane performance data.

Structure and dynamics of polyamide selective layers in reverse osmosis membranes

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.