Investigation On The Preparation Of Porous Nanofibers Based On The Self-assembly Of Block Copolymer

Owing to its unique structural characteristics,porous nano-electrospun fiber possesses large specific surface area,high aspect ratio and porous volume,which shows promising prospect in several fields,such as biological sensors,drug release,energy devices,environmental purification,catalysis and so on.At present,the porous structure on the surface of electro-spinning mainly originates from the phase separation behavior between polymers and solvents or the one between two components of polymer blends.However,the porous structure formed based on this mechanism presents relative wide pore size distribution,thus,the uniform of the porous structure still has space to be improved.In this thesis,we combined the electrospinning technology with the self-assembly of block copolymer?BCP?and fabricated the nano-electrospun fiber containing surficial pores with uniform structure on the basis of the specific macro-phase morphology formed by the self-assembly of BCP.Due to the strong immiscibility between styrene and 4-vinylpyridine,this thesis investigated the formation of porous structure on the surface of electrospun fiber based on the phase separation behavior of Polystyrene-block-Poly?4-vinylpyridine?copolymer?PS-b-P4VP?.The results were as follows:1.The morphology of PS-b-P4VP nano-electrospun fiber has been investigated through discussing the influences factors during the solvent annealing and the selective swelling processes,included the selective solvent for swelling,annealing solvent as well as time of annealing.The experimental results demonstrated that acetone as the co-solvent for both PS and P4VP could effectively induce phase separation of PS-b-P4VP electrospun-fibers while maintaining the fibrous-shape of the material.After P4VP chains were swollen and collapsed by immersing the fibers into ethanol,a certain amount of circular pore presented on the surface of PS-b-P4VP fibers.Unfortunately,due to the orientation of the polymer segments along the axial direction of the fibers resulting from the electrospinning processing,it is not easy to form a large number of cylindrical micro-phase of P4VP sitting perpendicular to the surface of the fibers.Thus,the way combining the solvent annealing and the selective swelling is hardly to obtain densely porous structure on the surface of PS-b-P4VP electrospun-fibers.2.We introduced a method of Self-Assembly and Non-solvent Induced Phase Separation?SNIPS?,through immersed polytetrafluoroethylene?PVDF?fibers into solution of PS-b-P4VP to get fibers with a PVDF as core and PS-b-P4VP as its out layer,and discussed the influences factors during SNIPS processes included the concentration of PS-b-P4VP solution,immersion time and the additive on the surficial morphology of the fibers.The experimental results demonstrated that PVDF could be well-covered by PS-b-P4VP lay?mPVDF-BCP?when the PDA modified PVDF?mPVDF?was immersed into 4 wt.%PVDF solution for 10 min,and some pores appeared.The densely porous structure with average diameter of 36±6 nm was formed on the surface of mPVDF-BCP after we further added excessive copper acetate?Cu?Ac?₂?.The FT-IR and Contact Angle test under different pH condition further identified the successful coating of PS-b-P4VP over PVDF fibers and manifested the pH responsibility of mPVDF-BCP fibrous membrane.3.One membrane type of structured catalyst was fabricated by loading the gold nano-particles?Au NP?onto the obtained porous mPVDF-BCP fibrous membrane?Au/mPVDF-BCP?via in-suit synthesis.The loaded total of Au NP was 14.23 wt.%,and the average diameter of Au NP was 3.3±0.74 nm from the result of SEM,TEM,XRD and TGA.This composite nano-fibrous membrane exhibited good catalytical performance for the reduction of 4-Nitrophenol?4-NP?and maintained well-stability even after 10 reaction circles.In contrast to the traditional supported catalytics with nobel metal,this structured catalyst of Au/mPVDF-BCP nano-fibrous membrane is much easier for handling and recycling and is beneficial and promising in the practical application.Shortly,in this work,we successfully introduced SNIPS and fabricated PVDF electro-spun fibers with relative uniform porous structure on their surface based on the assembly of PS-b-P4VP copolymer.This pioneering work opens one approach to prepare electrospun-fiber with surficial isoporous structure which is supposed to be very promising to improve the functional properties of porous nano-fibers.