Dual- and multilayer composite membranes, consisting of poly(acrylic acid) (PAA) and poly(vinylidene fluoride) (PVDF), were synthesized by the plasma-induced polymerization technique. The dual-layer membrane had a dense PAA layer grafted onto a microporous PVDF substrate, whereas in the multilayer membranes, the grafted PAA and the PVDF layers were arranged in an alternating sequence (e.g., PAA/PVDF/PAA and PAA/PVDF/PAA/PVDF/PAA). These membranes were used in a pervaporation process to separate ethanol-water solutions. For the dual-layer membranes, the results indicated that the separation factor increased and the permeation flux decreased with increasing amounts of grafted PAA. For the case of grafting yield < 0.6 mg/cm(2), the composite membrane demonstrated poor separation. As the grafting yield reached 0.85 mg/cm(2), a sharp increase of the separation factor was observed. For the multilayer membranes, the pervaporation performances were very good, with high separation factors (on the order of 100) and reasonable permeation fluxes over a wide ethanol concentration range. (C) 2004 Wiley Periodicals, Inc.