Ultrathin membranes for gas separation and pervaporation prepared upon electrostatic self-assembly of polyelectrolytes

Composite membranes with ultrathin separation layer were prepared by alternating electrostatic adsorption of cationic and anionic compounds (polyelectrolytes and bolaamphiphiles) at porous supporting membranes such as Celgard 2400, PAN/PET (a polyethyleneterephthalate fleece coated with a thin layer of polyacrylonitrile) and Isopore (an etched ion-track polycarbonate membrane). As the ionic compounds poly(allylamine hydrochloride) (PAH), poly(styrenesulfonate sodium salt) (PSS), 1.4-diketo-3,6-diphenylpyrrolo-[3,4-c]-pyrole-4,4'-disulfonic acid and 10,12-docosadiyne-1,22-disulfate disodium salt were used. The composite membranes were studied on their gas permeation and pervaporation properties. The adsorption of 20 layer pairs of PAH/PSS at PAN/PET membranes was sufficient to reduce the argon flow to 7% of the initial value, while 60 bilayers reduced the flow to 0.1%. Gas flow rates of oxygen, nitrogen and argon were nearly identical, while the flow rate of carbon dioxide was higher by a factor of up to 2.4. Toluene/heptane pervaporation through composite membranes of 60 bilayers of PAH/PSS on PAN/PET gave a toluene enrichment from 20% in the feed to 24% in the permeate, while for ethanol/water permeation a water enrichment from 3% in the feed up to 50% in the permeate was found. (C) 1998 Elsevier Science S.A. All rights reserved.