Spray assembled, cross-linked polyelectrolyte multilayer membranes for salt removal.

The present study reports the synthesis of spray-coated cross-linked polyelectrolyte multilayer membranes. Membrane cross-linking was performed using alkyne-azide "click" chemistry, where alkyne and azide functional groups were used to modify the poly(acrylic acid) (PAA) and the poly(allylamine) hydrochloride (PAH) polyelectrolytes. The results demonstrate that deposition at lower ionic strength produced smoother and denser membrane structures. Pore size analysis using neutral poly(ethylene glycol) revealed a decrease in the membrane pore size as the degree of cross-linking was increased, resulting in the membrane rejecting divalent CaCl2 at levels of up to 80%, and 50% rejection of monovalent NaCl. When poly(sodium-4-styrenesulfonate) (PSS) was combined with small amounts of cross-linkable PAA, significant flux increases were observed in the multilayer membranes with no observable reduction in ion rejection.