Tailoring Polyelectrolyte\nMultilayer Nanofiltration\nMembranes by Aerosol-Assisted Printing: Insights into Membrane Formation\nMechanisms

Polyelectrolyte multilayer (PEM) membranes, with advantageous\nfeatures\nof versatile chemistry and structures, are driving the development\nof advanced nanofiltration (NF) membranes with exceptional performance.\nWhile developing a printing method holds great promise for the eventual\nmass production of these membranes, reports on the printing method\nand the underlying mechanisms of membrane formation are currently\nscarce. Herein, we develop an aerosol-assisted printing (AAP) system\nfor fabricating PEM NF membranes with highly tunable separation characteristics.\nOur study unveils the three stages of membrane formation from assembly\nof polyethylenimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS):\naerosol deposition, single PE layer formation, and PEM assembly. The\ndroplet deposition is governed by inertial impaction, and the deposited\nPEs migrate/entangle to form a single PE layer. The thicknesses of\nthe PE layer and PEM exhibit linear growth as the number of printing\nscan increases. Furthermore, PE interdigitation forms an effective\npolymeric network barrier, which increases the resistance to solute\nand water transport. By manipulating the PE deposition mass and layering,\nPEM membranes with tunable pore radii (0.40–0.56 nm) and water\npermeability (5–60 L·m<sup>–2</sup>·h<sup>–1</sup>·bar<sup>–1</sup>) were obtained for various\nwater treatment applications, ranging from micropollutant removal\nto humic acid filtration. Our study offers valuable mechanistic insights\ninto the PEM formation and precise structural adjustment via printing,\nthus facilitating scalable manufacturing and widespread applications\nof the PEM NF membranes.