Preparation And Morphology Of PVDF/PS-B-PNIPAAM Ordered Porous Composite Membranes

Block copolymer(BCPs)composed of two or more thermodynamically incompatible homopolymers self-assemble into periodic microdomains,have been demonstrated to be promising precursors in the fabrication of highly ordered nanoporous structures.Amphiphilic block copolymer membrane material has a narrow pore size distribution and high porosity,and the preparation conditions can be adjusted to adjust its mechanical properties,thus showing great potential in the field of highly selective separation membranes.The temperature-sensitive membranes based on PNIPAAm show attractive application prospects in many fields.However,the responsive properties of temperature-sensitive membranes prepared by conventional approach are far beyond the reach of application because of the wide distribution of pore size and the difference of PNIPAAm chain length and density on membrane surface.In this paper,based on the self-assembly of the block copolymer,the separation membrane with monodisperse pore size was prepared by the method of solvent annealing and selective swelling-induced pore-making process.The PS-b-PNIPAAm block copolymer was dissolved in CH3Cl solvent and then combined with conventional PVDF membrane or Si to prepare membrane.The phase separation was induced by solvent vapor annealing.By controlling the annealing time and the type of annealing solvent to get a regular phase-separation structure.The effects of different substrates,annealing time and annealing solvent on the phase separation behavior were investigated.The results show that the surface of the composite membrane based on commercial PVDF has better surface regularity.When the annealing time was extended,the morphology of the membrane pores was more perfect within a certain range.However,the morphology of the membrane pores on the surface was diminished over time.CH3Cl and THF as the annealing solvents induced PS-b-PNIPAAm phase separation,the degree of the block copolymer is greater than that of ethanol and methyl/ethyl alcohol,and the surface of the obtained composite membrane has higher regularity.The PS-b-PNIPAAm block copolymer was dissolved in solvent and then combined with conventional PVDF separation membrane to prepare PVDF/PS-6-PNIPAAm separation membrane.The separation membrane with monodisperse pore size was prepared by the method of solvent annealing and selective swelling-induced pore-making process based on self-assembly of block copolymers.The effect caused by annealing solvents and swelling time on microstructure of separation membrane was discussed.The results indicated that the extension of swelling time resulted in the change of compact,PNIPAAm content increased on membrane surface,hydrophilicity enhanced and contact angle decreased and the water flux showed a little thermal sensitivity.Oncomparision,when CH3Clas annealing solvent,the composite membrane has better thermal sensitivity than THF.