Abstract
Increasing the net fixed-charge density in multilayer polyelectrolyte membranes using postdeposition reactions results in large enhancements of ion-transport selectivity. To control the fixed-charge density in poly(acrylic acid)/poly(allylamine hydrochloride) (PAA/PAH) films, we partially derivatized PAA using 2-nitrobenzyl bromide. The underivatized −COO- groups still allow adsorption of PAA/PAH membranes on a permeable support, while postdeposition UV irradiation of these films cleaves the 2-nitrobenzyl esters to form fixed-charge sites. Diffusion dialysis experiments show that PAA/PAH membranes prepared with 23%, 50%, and 65% 2-nitrobenzyl esterified PAA exhibit Cl-/SO42- selectivities of 100, 150, and 170, respectively (after photolysis). Underivatized PAA/PAH membranes show a selectivity of only 10. The order of magnitude increase in selectivity resulting from derivatization occurs with a minimal decrease in Cl- flux. By modifying PAH with photolabile 2-nitrobenzyloxycarbonyl groups, we also introduc...
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