Polyacrylonitrile (PAN) composite membranes with surface properties designed by either a chemical modification with ethylenediamine (EDA), or layer-by-layer (LbL) polyelectrolyte adsorption were investigated in this paper. Fourier-transformed infrared (FTIR) spectroscopy and streaming potential measurements showed that the first step of the reaction with EDA in gas phase was the formation of ammonium salts with the reactive carboxylic groups present on the surface of the starting membrane. Part of the ammonium carboxylate groups was transformed in secondary amide linkages by a heat-induced reaction. Poly(sodium styrenesulfonate) (NaPSS) and a polycation containing about 95 mol % of N,N-dimethyl-2-hydroxypropyleneammonium chloride units in the backbone (PCA(5)) were used as opposite polyions in the LbL film construction. The adsorbed polyion amount per every layer was controlled by the nature and concentration of the supporting electrolyte in polyelectrolyte deposition solution (NaBr and KBr). An almost linear increase of the adsorbed polyion amount versus the layer pair number was observed. The swelling degree (SD) in pure alcohols of the LbL-modified PAN composite membrane decreased with the increase of the solvent polarity and with the decrease of the pore volume by pore filling with polyelectrolyte complex multilayer. (c) 2005 Wiley Periodicals, Inc.