The separation of an ethanol-water solution by steady-state pervaporation was investigated. Poly (acrylonitrile-co-acrylic acid) was prepared and used as a membrane. The permeate flux and separation factor were measured over the full range of ethanol-water composition at temperatures 30, 40 and 50degreesC. Pervaporation exhibited negative deviations from ideal pervaporation behavior and the separation factors obtained varied from 5.4 to 31, depending on the composition of the feed mixture, and the temperature and the content of acrylic acid (AA) in copolymer membrane. Water clustering and strong water-alcohol interaction within the copolymer membrane can be considered in interpreting the observed pervaporation and selectivity. (C) 2004 Elsevier B.V. All rights reserved.