Controlling Ion Transport through Multilayer Polyelectrolyte Membranes by Derivatization with Photolabile Functional Groups

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-/SO4 2- 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 introduced net, fixed positive charge into PAA/PAH films and improved cation (Na+/Mg2+) selectivity. Transport simulations suggest that both Donnan exclusion and selective diffusion contribute to selectivity.

One layer, two layers, etc. An introduction to the EIS study of multilayer electrodes. Part 1: Theory

“…This is in perfect agreement with their attempt of modelling ion transport through a multilayer polyelectrolyte membrane [25], where the multilayer was assumed to behave as a simple monolayer (ion transfer phenomena at interfaces between two polyelectrolyte layers neglected, and same average diffusion coefficient for all layers, D), and where ion depletion in solution was neglected. This simplifying approach was also similar to that of other research groups such as those of Schlenoff et al [26][27][28][29], Tieke et al [30], and Labbé et al [31], for their studies of multilayer electrodes with voltammetric methods.…”

“…Since self-assembled polyelectrolyte multilayers [18] can be deposited on metallic surfaces (Pt, Au, glassy carbon, etc. ), it is very probable that multilayer electrodes will mark the years to come [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34].…”

Enhancing the Ion-Transport Selectivity of Multilayer Polyelectrolyte Membranes

“…Additionally, Cl À transport through these films is within 20 % of that through similar PAA/PAH membranes, showing that selectivity can be achieved without a significant diminution of flux. [38] A simpler, but perhaps less controlled, method for inserting charges into MPMs is to use metal-ion complexes as templates for ion-exchange sites. We partially complexed the carboxylate groups of PAA with Cu 2 , and then formed PAA-Cu 2 / PAH films.…”

Layer‐By‐Layer Self‐Assembly of Metal Nanoparticles on Planar Substrates: Fabrication and Properties

“…Further layering necessitates adjusting the pH of the polyelectrolyte solutions above the pK a of PAA. Hence, a fixed charge is introduced within the film by photolysis of the 2-nitrobenzyl groups [67]. Varying the fixed charge of such multilayers may be achieved by first complexing the carboxyl groups with mono-or divalent metal ions.…”