Dopamine-induced nonionic polymer coatings for significantly enhancing separation and antifouling properties of polymer membranes: Codeposition versus sequential deposition

Nonionic polymers (i.e., poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA), poly(N-vinyl pyrrolidone) (PVP), and poly(N-acryoyl morpholine) (PACMO)) have been reported as promising antifouling materials for membrane surface modification. Better understanding of similarity and difference for the nonionic polymers in terms of hydration capability and antifouling property will benefit the design and development of antifouling surfaces. Herein, two simple and scalable methods yielded composite coatings on the hydrophobic polymer membrane surfaces: (i) a codeposition of polydopamine (PDA) with PEG (or PVA) (labeled as MPDA-PEG and MPDA-PVA), and (ii) a sequential deposition featuring dopamine polymerization followed by the self-assembly of PVP (or PACMO) (labeled as MPDA-PVP and MPDA-PACMO) via hydrogen-bonded interactions. The results suggested that hydrophilicity and surface free energy of all modified membranes were significantly enhanced after introducing PDA and nonionic polymers. The order of improved initial water flux of these modified membranes was MPDA-PEG > MPDA-PVP ≈ MPDA-PVA > MPDA-PACMO. It was appeared that the codeposited membranes (MPDA-PEG and MPDA-PVA membrane) with excellent hydration capability and permeability had better antifouling property. However, antifouling property and durability were remarked for the sequentially deposited membranes (MPDA-PVP and MPDA-PACMO membrane) in comparison to the codeposited membranes as evaluated in protein filtration, oil/water emulsion filtration, and humic acid filtration. The hydration capability of hydrogen-bonded PDA-PVP (or PDA-PACMO) coating endows the sequentially deposited membranes with robust and comprehensive performance. This work systematically demonstrates that coating architecture is a vital role in the design of the nonionic polymer modified membranes.