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• Quaternary ammonium and zwitterion dual-functionalized PDB- b -PSB brushes on MF membrane surface were fabricated. • The membrane pore size was not significantly changed by the coating. • Surface hydrophilicity of M/PDB- b -PSB membrane enhanced obviously. • M/PDB- b -PSB membrane with passive anti-adhesive and upper active biocidal properties. • Modification strategy for ant-biofouling membrane was facile and promising. In order to improve permeability and biofouling resistance of microfiltration (MF) membranes, quaternary ammonium and zwitterion dual-functionalized diblock polyelectrolyte copolymers, poly(dimethylaminoethyl methacrylate-butylammonium bromide)- b -poly(sulfobetaine methacrylate) (PDB- b -PSB) prepared via RAFT polymerization, were immobilized on commercial poly(vinylidene fluoride) (PVDF) MF membrane surface via using a versatile and facile mussel-inspired method to fabricate hierarchical copolymer brushes. Hierarchical PDB- b -PSB brushes contained bottom passive anti-adhesive zwitterionic PSB layer and upper active biocidal quaternary ammonium PDB layer. The surface chemical composition and morphology characterizations of pure and modified membranes demonstrated that PDB- b -PSB copolymers were successfully grafted to the dopamine-modified membrane surface via thiol mediated Michael addition reaction, which did not significantly change the membrane pore structure. However, the initial contact angle of PDB- b -PSB modified membrane (M/PDB- b -PSB) was changed from 128° for pure membrane (M/pure) to 43.2° and became 0° within 10 s, indicating the enhanced hydrophilicity. More importantly, the M/PDB- b -PSB membrane exhibited active biocidal effects against E. coli and S. aureus with inhibition rates over 98% and the E. coli and S. aureus suspension fluxes of M/PDB- b -PSB membranes were 1.61 times and 1.35 times higher than those of M/pure membranes. The M/PDB- b -PSB membrane had excellent anti-biofouling property with a better water flux recovery rate of 72%, which was 30% higher than that of the M/pure membrane. Moreover, PDB- b -PSB brushes showed a good immobilization stability. Therefore, the approach of poly(dopamine)-assisted fabrication of anti-biofouling MF membranes with quaternary ammonium and zwitterion dual-functionalized diblock copolymers had a prospect application in membrane-based separation technology and water purification. [ABSTRACT FROM AUTHOR]

• Three kinds of comb-shaped amphiphilic PEME triblock copolymers were synthesized. • Effects of PEME with different hydrophilic block length on membrane structure-property relationship. • M-2 membrane exhibited high BSA solution flux (150 L·m−2·h−1) and excellent rejection (99.99%). • M-2 membrane overcame the permeability-selectivity trade-off for BSA solution separation. In order to reduce membrane fouling and fabricate highly selective membranes with high water permeability, three kinds of comb-shaped amphiphilic triblock copolymers, poly[poly(ethylene glycol) methacrylate]- b -poly(methyl methacrylate)- b -poly[poly(ethylene glycol) methacrylate] (PPEGMA- b -PMMA- b -PPEGMA, named as PEME), were synthesized via RAFT polymerization and used as modifiers to prepare poly(vinylidene fluoride) (PVDF) blend membranes by the non-solvent induced phase separation (NIPS) method. The effects of PEME with different hydrophilic PPEGMA length on the surface chemical structure, morphology, permeability and antifouling properties of the blend membranes were investigated detailedly. The results from ATR-FTIR and XPS tests confirmed that hydrophilic PPEGMA segments in PEME were enriched on the membrane surface due to PEME induced surface segregation. With the increase of the hydrophilic chain length in PEME, the mean pore size, porosity and roughness of the blend membrane increased gradually, indicating the modifier had the ability to adjust the membrane pore structure. Compared with pure membrane, the hydrophilicity of blend membranes was enhanced and the protein adsorption of representative bovine serum albumin (BSA) decreased obviously. After three cycles of the water-BSA-water, the M-2 blend membrane exhibited high BSA solution flux (150 L·m−2·h−1), excellent rejection (up to 99.99%) and satisfactory antifouling performance. In addition, compared with the recently published PVDF blend ultrafiltration membranes prepared by NIPS method, the M-2 membrane with surface small pore size, high flux, high selectivity and low fouling properties overcame the permeability-selectivity trade-off for BSA solution separation and showed a good application prospect for efficiently protein separation. [ABSTRACT FROM AUTHOR]