CHARACTERIZING POLYAMIDE REVERSE OSMOSIS MEMBRANES VIA SOLID-STATE NMR METHODS

NIEUWENDAAL, RYAN; STAFFORD, C. M.; KOROVICH, D; WITHERSPOON, V; SOLES, C. L.; VELASCO, MANUEL I.; WILBUR, J.

Congreso; V Taller Argentino de Resonancia Magnetica; 2023

Establishing clear relationships between the chemical structure, water/ion transport, and waterfiltration performance in the salt selective polyamide (PA) layer of thin film composite (TFC) reverseosmosis (RO) is important for designing water filtration membranes, yet these relationships aredifficult to establish. For instance, Ag+ probe Rutherford backscattering experiments(https://doi.org/10.1021/es8002712) showed that commercial polyamide membranes exhibitnegligible amine populations, whereas recent 15N {1H} NMR work(https://doi.org/10.1016/j.memsci.2019.03.037) showed amines comprise ~10% of the nitrogen in asimilar membrane.In this talk, I will discuss solid-state NMR results for determining composition in four trimesoylchloride (TMC)/isophthaloyl chloride (IPC)/metaphenylene diamine (MPD)-based TFC membranes thatwere fabricated at the pilot plant at Dupont Water Solutions. In these films the crosslink density wasintentionally reduced by replacing trifunctional crosslinking TMC monomers with their linear IPCdifunctional analog. While our results demonstrate that solid-state NMR measure the crosslinkdensity and composition directly, we unexpectedly revealed that both crosslink density and polarityare important design criteria in RO membranes.The composition and crosslink density values were measured via 13C CPMAS spectra, and I willdiscuss the acquisition parameters that were important for reducing error bars of in 13C NMRresonance intensities, including the Hartmann-Hahn match, the contact time, and the receiver phase.Optimizing of these parameters led to a improvement in accuracy of almost an order of magnitude,and ultimately allowed analysis of compositions that varied by only a few percent.If time allows, I will also discuss some recent results from our lab on water swollen polyamidemembranes aimed at studying polymer dynamics and water transport. We have performed quasi-elastic neutron scattering, 1H field cycling and diffusometry NMR of H2O- and D2O-swollenpolyamides for determining models of transport in these nanoporous films.