Construction of a Covalent Crosslinked Membrane Exhibiting Superhydrophilicity and Underwater Superoleophobicity for the Efficient Separation of High-Viscosity Oil–Water Emulsion Under Gravity

The separation of high-viscosity oil-water emulsions remains a global challenge due to ultra-stable interfaces and severe membrane fouling. In this paper, SiO₂ micro-nanoparticles coated with polyethyleneimine (PEI) were initially loaded onto a stainless steel substrate. This dual-functional design simultaneously modifies surface roughness and wettability. Furthermore, a covalent crosslinking network was created through the Schiff base reaction between PEI and glutaraldehyde (GA) to enhance the stability of the membrane. The membrane exhibits extreme wettability, superhydrophilicity (WCA = 0°), and underwater superoleophobicity (UWOCA = 156.9°), enabling a gravity-driven separation of pump oil emulsions with 99.9% efficiency and a flux of 1006 L·m^-2·h^-1. Moreover, molecular dynamics (MD) simulations demonstrate that the SiO₂-PEI-GA-modified membrane promotes the formation of a stable hydration layer, reduces the oil-layer interaction energy by 85.54%, and exhibits superior underwater oleophobicity compared to the unmodified SSM. Efficiency is maintained at 99.8% after 10 cycles. This study provides a scalable strategy that combines covalent crosslinking with hydrophilic particle modification, effectively addressing the trade-off between separation performance and membrane longevity in the treatment of viscous emulsions.