A novel hydrophilic nanocomposite additive （TiO2-g-PNIPAAm） was synthesized by the surface modification of titanium dioxide （TiO2） with N-isopropylacrylamide （NIPAAm） via ＂graft-from＂ technique. And the nanocomposite membrane of poly（vinylidene fluoride） （PVDF）/TiO2-g-PNIPAAm was fabricated by wet phase inversion. The graft degree was obtained by thermo-gravimetric analysis （TGA）. Fourier transform infrared attenuated reflection spectroscopy （FTIR-ATR） and X-ray photoelectronic spectroscopy （XPS） characterization results suggested that TiO2-g-PNIPAAm nanoparticles segregated on membrane surface during the phase separation process. Scanning electron microscopy （SEM） was conducted to investigate the surface and cross-section of the modified membranes. The water contact angle measurements confirmed that TiO2-g-PNIPAAm nanoparticles endowed PVDF membranes better hydrophlilicity and thermo-responsive properties compared with those of the pristine PVDF membrane. The water contact angle decreased from 92.8~ of the PVDF membrane to 61.2~ of the nanocompostie membrane. Bovine serum albumin （BSA） static and dynamic adsorption experiments suggested that excellent antifouling properties of membranes was acquired after adding TiO2-g- PNIPAAm. The maximum BSA adsorption at 40℃ was about 3 times than that at 23 ℃. The permeation experiments indicated the water flux recover ratio and BSA rejection ratio were improved at different temperatures.
A novel method for the surface modification of PVDF porous membranes was introduced. Styrene-（N-（4- hydroxyphenyl） maleimide） alternating copolymer SHMI-Br was blended with PVDF to fabricate SHMI-Br/PVDF membranes. The C-Br bond on the SHMI-Br/PVDF membrane was served as initial site of ATRP, and P（PEGMA） brush was grafted on the PVDF membrane. Attenuated total reflectance-Fourier transform infrared spectroscopy （ATR/FTIR） was used to prove the P（PEGMA） brushes were successfully grafted onto the SHMI-Br/PVDF membrane surface. Introduction of P（PEGMA） brushes on the PVDF membrane surface enhanced the hydrophilicity effectively. When the PEGMA degree of grafting was 16.7 wt%, the initial contact angle of PVDF membrane decreased from 98° to 42°. The anti-fouling ability of PVDF membrane was improved significantly after P（PEGMA） brush was ~afted. Taking the PEGMA degree of grafting 16.7 wt% as an example, the flux of protein solution was about 151.21 L/（m h） when the pH value of the BSA solution was 4.9. As the pH value was increased to 7.4, the flux was changed to 180.06 L/（m2 h）. However, the protein solution flux of membrane M3 （PEGMA： 0 wt%） was only 73.84 L/（m2 h） and 113.52 L/（m2 h） at pH 4.9 and 7.4, respectively.
