Polyamide Nanofiltration Membranes from Surfactant‐Assembly Regulated Interfacial Polymerization: The Effect of Alkyl Chain

Abstract Regulating the monomer diffusion during interfacial polymerization (IP) process is the key for tailoring the pore structure and desalination performance of thin‐film composite polyamide nanofiltration (NF) membrane. Recently a surfactant‐assembly strategy to regulate IP process and NF membranes with sub‐Å separation precision is proposed. However, little is known for the role of the molecular structure of surfactant on IP process and membrane performance. In this work, five sulfate surfactants with different length of alkyl chains are used to construct surfactant monolayer assembly at the water/hexane interface to regulate IP process. The results show that for the sulfate surfactants, the longer the alkyl chain, the more uniform the pore size distribution of polyamide active layer is and the higher the ion separation selectivity of NF membrane is. Among them, the NF membrane prepared from sodium n‐hexadecyl sulfate (SHS) exhibits the highest separation performance with the rejection of Na 2 SO 4 , MgSO 4 , MgCl 2 , and CaCl 2 up to 99.39%, 99.12%, 98.09%, and 97.38%, respectively. Overall, this study further confirms the regulatory role of surfactant‐assembled monolayer during IP process and provides important insights into how the polyamide structure and the resulting NF membranes are influenced by the alkyl chain length of the surfactants.