Anti(-bio)fouling Nanostructured Membranes Based on the Cross-Linked Assembly of Stimuli-Responsive Zwitterionic Microgels

This study embodies the development of a thermoresponsive nanostructured antifouling membrane based on cross-linkable zwitterionic microgels for tunable water filtration and molecular separation applications. The zwitterionic vinylimidazole propane sultone (VIPS) comonomer was synthesized by reacting vinylimidazole with 1,3-propane sultone. The microgels were synthesized utilizing a one-step precipitation polymerization approach by taking 10 and 20 wt % of the VIPS with N-isopropyl acrylamide (NIPAm), 2-aminoethyl methacrylate (AEMA), with the cross-linker N,N′-methylene bis(acrylamide) (BIS) to produce MG-10 and 20, respectively. Various chemical and morphological characterizations were carried out to establish the synthesis and characteristics of microgels. Suction filtration of a dilute MG-20 dispersion was used to construct cross-linked microgel membranes of different thicknesses over a track-etched membrane support in the next step. Surface and morphological analyses validate the packed microgel layer formation. The constructed layer was temperature-switchable, resulting in a twofold increase in water flux from room temperature to 40 °C. The thin and closely packed microgel particles resulted in a sub-2 nm surface pore size, allowing for strong rejection (>99%) of small molecules. Because of the presence of VIPS, both of the microgels displayed excellent anti(-bio)fouling properties against bacterial and protein foulants. The surface demonstrated ultralow protein adsorption and a high flux-recovery ratio (>90%), resulting in antifouling performance. The stability of the cross-linked robust microgel layer without any leaching warrants dimensional stability and long-term permeability. This smart gating membrane with improved anti(-bio)fouling activity expands the scope of thermoresponsive microgel-based nanostructured membranes and has significant potential in water purification and molecular separation applications.