Antifouling and pH‐Responsive Ultrafiltration Membrane of PAA‐co‐NH ₂ /PEOX‐co‐NH ₂ Multilayer for Protein Purification

Membrane fouling has been a persistent challenge in the protein ultrafiltration process. Stepwise interfacial complexation demonstrates an effective strategy to improve anti‐fouling property. The poly(acrylic acid)/poly(2‐ethyl‐2‐oxazoline) (PAA/PEOX) multilayer exhibits excellent anti‐fouling property, yet only applied in acid environment (pH < 5). Herein, the amine‐crosslinked (PAA‐co‐NH 2 /PEOX‐co‐NH 2 ) n membranes are fabricated, which show broadened pH stability (pH 2∼12) upon FT‐IR characterization. In addition, the static BSA adsorption and dynamic cyclic filtration results confirm the superior anti‐fouling property of the (PAA‐co‐NH 2 /PEOX‐co‐NH 2 ) n membranes, displaying 30%–57% decline in static BSA adsorption and 54%–76% decrease in total fouling ratio compared to PVDF. It contributes to their enhanced hydrophilicity (53°), smoother surface (22.3 nm), and increased negative surface charge (−22.5 mV) compared to PVDF (89°, 33.8 nm, and −11.4 mV). Benefiting from the chain conformation transformation of PAA‐co‐NH 2 , membranes possess remarkable pH‐triggered cleaning ability, leading to a ∼100% recovery in water flux. Moreover, the membranes exhibit superior water flux (227 L·m −2 ·h −1 ) and BSA retention (97%) compared to PVDF (retention, 63%). This work provides a facile and effective strategy to develop polymer complex‐based coatings with pH‐response and anti‐fouling property to improve protein separation performance for ultrafiltration membranes.