Ultrafiltration Membrane with High Stability and Anti-fouling Performance Fabricated via Stepwise Interfacial Complexation of Charged Polytrifluorostyrene.

Surface coating of polymer complexes driven by electrostatic interaction represents a facile strategy for membrane modification. However, chemical stability is still a major issue for the application of such polymer coatings and the study of polymer complex-modified membranes for ultrafiltration is less explored. In this study, positively charged quaternized poly(trifluorostyrene) (QPTFS) and negatively charged sulfonated poly(trifluorostyrene) (SPTFS) are synthesized and used to prepare ultrafiltration membranes through stepwise interfacial complexation. The successful complexation between QPTFS and SPTFS is verified using quartz crystal microbalance and spectroscopic ellipsometry. The separation performance of the modified membranes is evaluated and the QS-2 membrane (containing two bilayers of polymer complexes) demonstrates a desired water flux of 378 L m^-2 h^-1 bar^-1 and an excellent BSA rejection of 96.8%. Moreover, the QPTFS/SPTFS selective layer exhibits remarkable stability against saturated NaCl or at extreme pHs, and its separation performance is maintained with BSA rejection above 95%. The cyclic filtration indicates the enhanced anti-fouling performance upon QPTFS/SPTFS decoration, in which the flux recovery rate of QS-2 is ≈3-fold higher than that of polyvinylidene fluoride substrate. This work proposes an accessible approach using charged fluoropolymers to achieve chemically stable ultrafiltration membranes with desired water flux, excellent protein separation performance and enhanced anti-fouling property.