Multiple stimuli-responsive poly(vinylidene fluoride) (PVDF) membrane exhibiting high efficiency of membrane clean in protein separation

Surface modification of poly(vinylidene fluoride) (PVDF) membrane is performed for preparation of multiple stimuli-responsive membrane. Poly(N-isopropylacrylamide) (PNIPAAm), poly(acrylic acid), and Fe3O4 nanoparticles are incorporated to the PVDF membrane surface to bring temperature-, pH-, and magnetism-responsive property to the membrane, respectively. The chemical structures and surface morphology of the modified PVDF membrane have been characterized with reflectance Fourier transform infrared, X-ray photoelectron spectroscopy, and scanning electron microscopy. The stimuli-responsive property of the membrane has been examined with the change of the water permeation fluxes. A dramatic change of water permeation flux appear at about 30 and 42 °C under the operation at pH=3.7 and pH=6.6, respectively The results demonstrates the dual temperature- and pH-responsive characteristic of the membrane. Moreover, incorporation of the magnetic Fe3O4 nanoparticles to the membrane surface makes the membrane becoming a magnetism-responsive material and brings the magnetothermal property to the membrane. Under an alternating magnetic field (100 kHz) for 5 min the membrane has shown a temperature increase from 29 to 40 °C due to the magnetothermal effect. The possibility to trigger the temperature-responsive property of the membrane with a remote magnetic field manner has been demonstrated. The temperature- and magnetism-responsive property also provide a driving force for release of protein foulants from the membrane surface in bioseparation. As a result, the surface-modified PVDF membrane shows multiple stimuli-responsive characteristics and high efficiency of membrane clean in protein separation.