Our study is concerned with the development of a novel type of layer-by-layer (LbL) self-assembled membrane from a single cationic polyelectrolyte (PE) and blended anionic PEs. Their synthetic seawater stability is investigated as a function of PE type and blend ratios using quartz crystal microbalance-dissipation (QCM-D). These materials adsorbed into multilayers with significant viscoelasticity. Poly(allylamine hydrochloride) (PAH) and poly(vinylamine hydrochloride) (PVA) based LbL blend films did not show any multilayer decomposition with the addition of synthetic seawater regardless of blend ratio while chitosan based multilayers disintegrated. The flux of PVA based blend membrane to water with 1,000 ppm NaCl was found to be 6.7 L/m(2).h at 40 bar and the flux properties of the membranes were highly dependent on both the thickness and hydrophilicity of multilayers. Ion rejection can be controlled with the charge of the top layer consistent with a Donnan exclusion approach. Sodium ion rejection of 60.5 layered LbL blend membrane was 98.4% at 40 bar and it was determined that sodium ion rejection improved 110.7% compared to a commercial nanofiltration membrane. POLYM. ENG. SCI., 60:1006-1018, 2020. (c) 2020 Society of Plastics Engineers