Properties of poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide) membranes prepared by alkali treatment

An amphiphilic graft copolymer (PVDF-g-PNIPAAm) with poly(vinylidene fluoride) (PVDF) main chains and poly(N-isopropylacrylamide) (PNIPAAm) side chains was synthesized via radical copolymerization, and flat sheet membranes of this copolymer were prepared by the phase inversion method. The process of membrane formation was investigated by ultrasonic time-domain reflectometry (UTDR). The structures and properties of the membrane, including its surface chemical structure, pore morphology, and water permeability, were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and a water permeation experiment, respectively. The relationship between the process of membrane formation and the properties of the membrane was studied. The results showed that the membrane displayed temperature sensitivity. Treating the PVDF for a longer period with alkali caused more PNIPAAm to graft onto the main chains, which influenced not only the microporous structure and formation process of the membrane but also the temperature sensitivity of the performance of the membrane.