Probing Water and Ion Diffusion in Functional Hydrogel Membranes by PFG-NMR

High Resolution Image Download MS PowerPoint Slide The effects of ligand basicity on water and ion transport within hydrogel membranes are investigated using a library of functionalizable poly(ethylene glycol) diacrylate (PEGDA) polymer networks with the same cross-link density. Pulsed-field gradient NMR characterization of membranes grafted with Lewis base ligands sorbed with a model lithium triflate electrolyte reveals that the self-diffusion of water molecules and ions is primarily driven by the hydration level of the membrane, with the ligand functionality playing a secondary role. A comparison of lithium triflate and lithium chloride electrolytes demonstrates greater salt uptake and lower Li + and water self-diffusion values for membranes swelled with lithium triflate electrolytes, suggesting that stronger triflate–polymer interactions impede transport within the membrane. These findings are further corroborated by atomistic molecular dynamics simulations that reveal significant coordination between the triflate anion and the polymer, reducing the ion and water mobility. These mechanistic insights into the respective roles of membrane hydration and specific-ion effects on transport within ligand-functionalized membranes lay the groundwork for designing high performance membranes for targeted solute separation.