Surface modifying macromolecules (SMMs) were used to modify the top surface of polymeric membranes. SMMs are oligomeric fluoropolymers synthesized by polyurethane chemistry and tailored with fluorinated end groups. In this study, the surface of polyetherimide (PEI) flat-sheet membranes prepared by the phase inversion method was modified using 2 wt.% of SMM and 15 wt.% PEI concentration in the polymer casting solution. The effect of solvent evaporation time on membrane surface modification was investigated. X-ray photoelectron spectroscopy analysis shows enrichment of fluorine on the modified PEI membrane surfaces and their contact angles were higher than those of the unmodified PEI membrane. Both the surface fluorine content and contact angles of the SMM/PEI blended membrane increased when the solvent evaporation time was increased up to 5 min. The SMM modified and unmodified PEI membranes were characterized by means of tapping mode atomic force microscopy (TM-AFM). The mean pore size, nodule size, pore density, surface porosity and mean roughness of the modified membranes were determined and compared with those of the unmodified membrane. (C) 2004 Elsevier B.V. All rights reserved.