Membrane surface engineering with hyperbranched polylysine for effective oil-water emulsion separation

The use of hydrophilic polymers for anti-oil-fouling modification of PVDF oil-water separation membranes has been extensively studied. However, the effects of different molecular structures of polymers on the membrane separation process remain unclear. Hyperbranched polylysine (HBPL) is a promising candidate for hydrophilic modification of PVDF membranes due to its branched structure and numerous amino groups. In this study, a HBPL grafted PVDF (PVDF-g-HBPL) oil-water separation membrane was designed and compared with a linear ε-polylysine (ε-PL) grafted PVDF (PVDF-g-PL) membrane. The 1 H NMR, FTIR, XPS, and SEM confirmed that the HBPL was successfully synthesized and grafted onto the PVDF membrane. The PVDF-g-HBPL membrane exhibited better separation performance and oil fouling resistance compared to the PVDF-g-PL membrane. The oil-water separation efficiency for various emulsions surpassed 90 %, and the membrane showed chemical stability under different pH conditions. Additionally, the PVDF-g-HBPL membrane showed low adhesion force, particularly under acidic or alkaline conditions, and ultralow shear friction during tangential underwater oil adhesion tests. Classic molecular dynamics (CMD) simulations revealed that the HBPL forms a stronger hydration layer and has weaker interactions with the oil molecules than the linear PL. This work highlights the importance of the hyperbranched structure in the oil-water separation system and expands the application of hyperbranched polymers in designing novel oil-water separation membranes.