The antifouling mechanism of a novel polyacrylonitrile (PAN) ultrafiltration (UF) membrane incorporating the amphiphilic comb copolymer additive, polyacrylonitrile-graft-polyethylene oxide (PAN-g-PEO), has been investigated using a laboratory-scale cross-flow test unit and atomic force microscopy (AFM). In fouling tests with a bovine serum albumin (BSA) solution, PAN UF membranes incorporating 20% PAN-g-PEO possessed excellent antifouling characteristics, whereas a commercial PAN UF membrane showed severe pore blocking that followed with surface cake formation. The PAN-g-PEO/PAN blend membranes also exhibited fouling reversibility and constant BSA retention, which indicate their ability to separate macromolecules without altering the molecular weight cut-off. An AFM analysis with a model carboxylated colloid-probe measured no adhesion force with the blend membrane, while the commercial PAN membrane exhibited strong adhesion to the probe, consistent with the fouling properties of the membranes. The antifouling character of the blend membrane is attributed to the surface segregation and local orientation of PAN-g-PEO molecules at the membrane surface and pore walls during membrane casting, creating a dense PEO brush layer that provides a steric barrier to protein adsorption. (C) 2007 Elsevier B.V. All rights reserved.