Layered polyelectrolyte films as selective, ultrathin barriers for anion transport

Synthesis of high-flux composite membranes requires methods for deposition of ultrathin, defect-free films on highly permeable supports. Layer-by-laye r deposition of polyelectrolytes on porous alumina (0.02 mu m pore diameter ) produces such membranes. Electron microscopy shows that five bilayers (<2 5 nm) of poly(allylamine hydrochloride) (PAH)/poly(styrenesulfonate) (PSS) are sufficient to cover porous alumina and that underlying pores are not cl ogged during the deposition process. The selectivity of anion transport thr ough these membranes increases with the number of bilayers until the substr ate is fully covered. Five-bilayer PAH/PSS membranes have Cl-/SO42- and Cl- /Fe(CN)(6)(3-) selectivity values of 7 and 310, respectively. PAH/poly(acry lic acid) membranes show selectivity values similar to those of PAH/PSS mem branes but with a 3-fold decrease in anion flux. Selectivity in both of the se systems likely results from Donnan exclusion.