P(HEMA-co-PEGDA) hydrogel coated PVDF Janus membrane with superior evaporation efficiency prepared via interfacial free radical polymerization

Membrane distillation (MD) technology is crucial for achieving zero discharge of hypersaline wastewater. However, its practical application has been hindered by low permeation flux. This study presents a hydrogel-coated Janus membrane (JM), developed through controlled interfacial free radical polymerization (IFRP) on a self-fabricated hydrophobic polyvinylidene fluoride (PVDF) substrate under ultraviolet irradiation. Microscopic images show that the in-situ synthesized hydrogel infiltrated into the nanoscale pores of the PVDF substrate, forming a stable "physical interlocking" composite structure with an impressive hydrophilic modification depth of 42 μm. MD performance results indicate that the optimized M-P2H4 JMs achieve remarkable water vapor flux of 42.14 L m -2 h -1 , while maintaining stable flux and salt retention across various salt concentrations (3.5wt%-20wt%). Molecular dynamics simulations reveal a strong interaction energy between the synthesized hydrogel layer and water molecules. Dark evaporation tests, differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) analysis show that the hydrogel networks increase intermediate water proportion and remarkably reduce evaporation enthalpy. Higher specific surface area is measured for the microsphere-based PVDF membrane, thereby increasing the evaporation area. The combination of the reduced evaporation energy barrier and increased evaporation area of M-P2H4 result in its excellent evaporation efficiency, which also presents excellent resistance to surfactant-stabilized oil-in-water brine emulsions. This study offers valuable insights into designing JM with high flux capability and superior anti-fouling properties.