Ion-exchange membranes prepared using layer-by-layer polyelectrolyte deposition

Layer-by-layer polyelectrolyte adsorption in porous polymeric membranes provides a simple way to create ion-exchange sites without greatly decreasing hydraulic permeability (<20% reduction in permeability). At 80% breakthrough, membranes coated with 3-bilayer poly(styrene sulfonate) (PSS)/polyethyleneimine (PEI) films bind 37 ± 6 mg of negatively charged Au colloids per milliliter of membrane volume. The binding capacity of membranes coated with 1-bilayer films decreases in the order PSS/PEI > PSS/poly(diallyldimethyl ammonium chloride) > PSS/poly(allylamine hydrochloride). Films terminated with a polyanion present cation-exchange sites that bind lysozyme, and the lysozyme-binding capacities of (PSS/PEI)3/PSS films increase with the ionic strength of the solution from which the last PSS layer is deposited. Charge screening during deposition of the terminal PSS layer gives rise to a larger number of ion-exchange sites and lysozyme binding capacities as high as 16 mg/mL of membrane. At 10% breakthrough, a stack of 3 membranes binds 3 times as much lysozyme as a single membrane, showing that stacking is an effective way to increase capacity.