Superamphiphilic zwitterionic block copolymer surfactant-assisted fabrication of polyamide thin-film composite membrane with highly enhanced desalination performance

A well-defined water-soluble superamphiphilic block copolymer surfactant containing superhydrophilic zwitterionic and very hydrophobic long alkyl units (PSbPDz) was synthesized via reversible addition-fragmentation chain-transfer polymerization for the replacement of the conventional surfactant used to polyamide (PA) thin-film reverse osmosis (RO) membrane. PSbPDz was found to act as a surfactant successfully, and work as a filler at the same time even after interfacial polymerization (IP) due to its entanglement effect of the polymer chains with the PA matrix. As the surfactant, PSbPDz improves the water wettability on the top surface of the support layers decreasing the thickness of the PA selective layer at the thinnest region and expands the interface area between the aqueous and organic phase increasing the roughness of the PA selective layer. As the filler, PSbPDz introduced into the PA selective layer increases the water wettability of the RO membrane. Hence, the RO membrane fabricated with 0.015 wt% of PSbPDz in the aqueous solution through IP shows much larger water permeance value (1.69 L m⁻² h⁻¹ bar⁻¹) than the neat RO membrane (0.68 L m⁻² h⁻¹ bar⁻¹) maintaining the high salt rejection value.