Engineering multifunctional thin-film composite polyamide membranes with water-soluble amphiphilic cationic block copolymer surfactants by regulating interfacial polymerization

초록

The regulation of interfacial polymerization (IP) assisted by surfactants plays a crucial role in improving the separation efficiency of thin-film composite (TFC) polyamide (PA) membranes. Herein, a series of amphiphilic cationic block copolymers were systematically synthesized as novel surfactants based on poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) with different hydrophobicity and charge density via reversible addition-fragmentation chain transfer (RAFT) polymerization. The hydrophobicity was controlled by fully quaternizing one PDMAEMA block with different long alkyl chains (C8, C12, or C16), while the charge density was tuned by varying the quaternization ratio (0, 50, or 100%) of the other PDMAEMA block with short alkyl chain (C2). The incorporation of these block copolymers into the m-phenylenediamine (MPD) aqueous solution was found to accelerate the MPD diffusion into the organic phase as suggested by sum-frequency vibrational spectroscopy (SFVS) measurements at the water/air interface together with interfacial tension measurements, thereby promoting the IP reaction and producing a thin, dense, and smooth selective layer. Among the water-soluble block copolymers, the addition of Q(C12)-Q50 possessing one hydrophobic block of fully quaternized PDMAEMA with 1-bromododecane and the other hydrophilic block of 50% quaternized PDMAEMA with 1-bromoethane as the surfactant yielded the highest water flux (32.6 Lm−2 h−1) while maintaining excellent salt rejection (99.0%). Furthermore, the membrane with Q(C12)-Q50 demonstrated remarkable antifouling, antibacterial, and operational stability characteristics, attributable to the smooth, hydrophilic selective layer containing residual block copolymer. Overall, these findings reveal that the block copolymer structure profoundly influences membrane morphology and separation performance by regulating the IP dynamics, offering new insights into the design of polymeric surfactants for fabricating multifunctional TFC PA membranes with superior desalination efficiency.

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