Poly(vinylidene fluoride) (PVDF) ultrafiltration membranes were prepared by immersion precipitation method using poly(hydroxyethyl methacrylate)-block-poly(methyl methacrylate) grafted silica (PHEMA-b-PMMA@SiO2) nanoparticles as additives. The hybrid nanoparticles were synthesized by the surface initiated atom transfer radical polymerization (SI-ATRP), and they were characterized in detail by FT-IR, TEM, DLS and GPC. Results confirm that core shell structure is formed after grafting PHEMA-b-PMMA brushes on the silica nanoparticles. Their average hydrodynamic diameter also increases with the prolongation of grafting time. After blending PVDF with the hybrid silica nanoparticles, the composite PVDF membranes exhibit high porosity and improved water permeation. Especially, when the molecular weight is 1.73 x 10(5) g/mol for PHEMA-b-PMMA on the hybrid nanoparticles, the water flux of the PVDF composite membrane is 2.5 times than that of the control PVDF membrane, while the rejection to bovine serum albumin (BSA) remains at a high level (> 90%). In addition, all the composite PVDF membranes show lower BSA adsorption and larger water flux recovery ratio than the control PVDF membrane. The improvement of membrane performance is attributed to the good hydrophilicity of PHEMA-bPMMA@SiO2 nanoparticles. Our results suggest that PHEMA-b-PMMA@SiO2 nanoparticles with moderate molecular weight of PHEMA-b-PMMA are suitable for the property optimization of PVDF-based composite membranes. (c) 2013 Elsevier Ltd. All rights reserved,