A novel water purification membrane has been prepared by layer-by-layer (LBL) assembly of tailored, core-shell star block copolymers. The star block copolymer consists of a hydrophobic polystyrene core (PS) and a plurality of charged hydrophilic arms (poly(N, N-dimethylaminoethyl methacrylate): PDMAEMA or polymethacrylic acid: PMAA). The high density of functional groups per unit volume of the PS-PDMAEMA and PS-PMAA star polymers enabled the formation of thin films with densely packed spherical morphologies, even with a low number of LBL cycles. The hydrophilic arms at the membrane surface helped mitigate membrane fouling, whereas the hydrophobic PS core suppressed undesirable swelling of the LBL-films in water, retaining good film durability. The star polymer films composed of 3.5 alternating layers of PS-PDMAEMA and PS-PMAA demonstrated an efficient nanofiltration capability of >98% rejection toward the small carcinogenic textile dye, Congo Red, with high water flux (ca. 40 LMH at 50 psi) at very low operation pressure. (C) 2015 Elsevier Ltd. All rights reserved.