Composite membranes with ultrathin separation layer prepared by self-assembly of polyelectrolytes

New composite membranes with ultrathin self-assembled polyelectrolyte separating layer and their use in gas, liquid and ion separation are described. Composite membranes were prepared by alternating electrostatic adsorption of polycations and polyanions on a porous PAN/PET supporting membrane (a polyethylenenterephthalate fleece coated with a thin layer of polyacrylonitrile). As the polycations poly(allylamine hydrochloride) (PAH), poly(ethylenimine) (PEI), poly(diallyldimethyl-ammonium chloride) (PDADMAC), poly(4-vinylpyridine) (P4VP) and chitosan (CHI) were used, the polyanion was always poly(styrene sulfonate sodium salt) (PSS). Studying CO2 and N-2 permeation rates, selectivities for CO2 (alpha = 1.5) were only found with P4VP/PSS separation layer. Studying ethanol-water pervaporation, separation factors alpha' up to 80 were found, when the separation layer was made of PAH/PSS and annealed at T greater than or equal to 60 degrees C. For non-annealed samples, the highest alpha' value was 20. It was found for a separating membrane of PEI/PSS. Various effects of preparation and operation conditions on flux and separation factor are discussed. Studying permeation of NaCl and MgCl2 in aqueous solution, a selective transport of the monovalent Na+ was found, if the separation layer was PAH/PSS. The permeation rate for Na+ was 15.1 times higher than for Mg2+. Our study indicates that composite membranes with self-assembled polyelectrolyte separation layer rue useful in materials separation, although individual polyions may exhibit a very different separation capability. (C) 1999 Elsevier Science S.A. All nights reserved.