The effect of divalent metal ions on conformational changes, size and hydrophilicity of poly(acrylic acid), PM, in solution as well as its relation with characteristics of adsorbed polymer layers on polyethersulfone membrane, PESm, were studied and analyzed by several techniques. PM adsorption on PESm in the presence of divalent metal ions was established to be occurring by an adsorption mechanism promoted by interchain polymer-metal bonds between polymer molecules in solution and pre-adsorbed polymer layers on the surface. Results suggest that changes of hydrophilic-lipophilic balance of polymer chains can be related to adsorption mechanisms of PM; these changes are consequence of decrease of negative charges on carboxylate groups by coordination of added metal ions and by increase of ionic strength. Besides, the surface and permeability characteristics of adsorbed polymer layers were related to the changes of size, aggregation and conformations of polymer chains in solution as metal ion concentration was increased. (C) 2011 Elsevier B.V. All rights reserved.