Surface wormlike morphology control of polysulfone/poly(N-isopropylacrylamide) membranes by tuning the two-stage phase separation and their thermo-responsive permselectivity

The preparation of thermo-responsive polymeric porous membranes with well-defined morphology and high mechanical strength is still a great challenge. In our work, high strength and self-supporting polysulfone/poly(N-isopropylacrylamide) (PSf/PNIPAm) membranes with tuning wormlike network morphology and thermo-responsibility were successfully prepared via the approach combining in situ cross-linking polymerization with vapor-liquid nonsolvent induced phase separation (V-LIPS). With increasing the NIPAm concentration and the exposure time during the VIPS process, the wormlike networks self-assembled on the membrane surfaces, and their diameter rapidly increased to ~ 63 nm in 60 s. As a result, the pore size/porosity of the membranes increased and the membrane hydrophilicity improved, leading to high water flux with a maximum value of ~ 222 L m−2 h−1 at 23 °C. Furthermore, the permselectivity of the fabricated membranes exhibited strong and fully reversible thermo-responsive character as feed temperature ranged from 23 to 50 °C, in which the thermo-responsive coefficient was as high as ~ 3.7 after viscosity correction and the size distribution of silver nanoparticles in the filtrates narrowed down sharply. In addition, the fabricated membranes with wormlike network morphology exhibited the maximum tensile strength of ~ 6 MPa and elongation at break of ~ 33%, which are much higher than the block copolymers based membranes with the similar morphology. The approach provided here opens a new and simple way to prepare high strength PSf membranes with tuning network morphology and thermo-responsive permselectivity in large scale, and which is expected to be expanded to fabricate other polymeric microporous membranes.