Abstract
In this study, thermo-responsive and magnetic poly(vinyldiene fluoride) (PVDF) membranes grafted with branched poly(N-isopropylacrylamide) (PNIPAAm) chains and magnetic Fe3O4 particles have been prepared. The preparation method includes three reactions. The first step is grafts of poly(acrylic acid) (PAA) chains to PVDF membrane surfaces. The PVDF membrane has been treated by ozone to generate peroxide and hydroperoxide groups on the PVDF membrane surface. Surface-initiated radical polymerization of acrylic acid (AA) is then carried out to introduce PAA chains to PVDF membrane surface. The second step is incorporation of PNIPAAm chains using amino-terminated PNIPAAm as areagent through the addition reaction between the carboxylic acid groups of PAA and the amine groups of PNIPAAm. Then Fe3O4 nanoparticles are then attached onto the surface of PVDF-AA-NIPAAm through the condensation reaction between the hydroxyl groups of Fe3O4 nanoparticles and the carboxylic acid groups of PAA. The chemical structures of the surface-modified PVDF membranes have been characterized with FTIR, ESCA and SEM. In water flux experiment, the water flux of the membrane increases with the increasing the temperatures because of the conformational change of the thermo-responsive PNIPAAm chains. The fluxes show a dramatically increase between 40 and 41.5 oC, which is corresponding to the the lower critical solution temperature (LCST) of the PNIPAAm chains. With solution under different pH values, the measured LCST’s increase with temperature increasing. Moreover, the PVDF-PAA-PNIPAAm-Fe3O4 membrane could be heated with an alternative magnetic field, as the presence of the magnetic Fe3O4 nanoparticles on the membrane surface. The magnmetothermal effect of the membrane is demonstrated. In the membrane cleaning tests, the membrane is fouled with BSA and then cleaned under different condition. A high flux recovery ratio has been obtained with the PVDF-PAA-PNIPAAm-Fe3O4 membrane to demonstrate its ease cleaning property. The thermally and magnetically-induced structure changes of the grafted layer of PVDF-PAA-PNIPAAm-Fe3O4 membrane contribute to the release of BSA from the membrane surface and the cleaning performance of the membrane.