Bijel-templated hydrogel membranes for pH-responsive water filtration

Hydrogels are cross-linked, hydrophilic polymer networks with growing applications in membrane filtration. However, their filtration performance is limited by fouling on the membrane surface. While nanoparticle coatings are well-known for providing anti-fouling properties, their incorporation into the hydrogel surface is hindered by nanoparticle agglomeration in many hydrogel polymers. In this work, we introduce the synthesis of hydrogel membranes with nanoparticle-decorated surfaces made from bicontinuous interfacially jammed emulsion gels (bijels) for pH-responsive water filtration. We fabricate bijel films by coating the bijel precursor onto flat-sheet substrates using roll-to-roll solvent transfer induced phase separation (R2R-STrIPS). Our study shows that the precursor wetting on the substrate and the nanoparticle surface modification with surfactant control the bijel structure and internal pore sizes. Hydrolysis converts the bijel films into polyacrylic acid hydrogels. Using confocal microscopy analysis, we reveal that the swelling of the hydrogel in response to increasing water pH leads to a closure of the membrane surface pores. Flux measurements show that the swollen hydrogel blocks water flow, while decreasing the water pH re-opens the hydrogel surface pores and enables water permeation. By the separation of emulsion droplets our bijel-hydrogel membranes showcase the potential of bijels as templates for smart microfiltration membranes for water filtration, drug delivery, and tissue engineering.