Hyperbranched Zwitterionic Polymers Functionalized Underwater Superoleophobic Microfiltration Membranes for Oil-in-Water Emulsion Separation.

Inspired by mussel adhesion chemistry, a kind of hydrophilic poly(vinylidene fluoride) (PVDF) microfiltration membranes with underwater superoleophobicity was prepared using thiolated hyperbranched zwitterionic poly(sulfobetaine methacrylate) (HPS) as a nanoscale surface modifier. The HPS was first synthesized via RAFT copolymerization and followed by sulfonation reaction, and then coated onto dopamine (PD) adhesive PVDF membranes via thiol-mediated Michael addition reaction. The successful and uniform coating of HPS onto the membrane surface was demonstrated by X-ray photoelectron spectroscopy and energy dispersive X-ray detector. The surface micro-nano morphology and increased roughness of the PD/HPS modified (M-PD/HPS) membrane were also investigated by field emission scanning electron microscope and atomic force microscope. The M-PD/HPS membrane could be wetted completely by water and the underwater oil contact angles were about 160o, indicating the M-PD/HPS membrane with excellent hydrophilicity and underwater superoleophobicity. Compared with the pure PVDF membrane, the M-PD/HPS membrane for hexane-in-water emulsion separation exhibited enhanced water filtration flux of 10707 L m-2 h-1 (0.1 MPa) and oil rejection ratio was above 99.9%. Besides, the excellent anti-fouling ability and recyclable properties of the M-PD/HPS membranes would make them suitable for a long time using. Thus, the approach of mussel adhesion chemistry employed the RAFT mediated nano-sized hyperbranched zwitterionic polymers as postmodification reagents showed a good application prospect in purification of oily waste water and oil recovery.