Preparation Of CS/PVA/Fe₃O₄ Composite Membranes And The Study Of Their Microstructure And Properties

Recently,magnetic responsive polymer composite membranes have been favored much attention mainly due to their unique microstructures in the various applications of gas separation,ultrafiltration and biomedicine.Researchers hope to prepare nano-magnetically responsive composites with excellent magnetic,electrical,optical,and mechanical properties by selecting functional fillers and adjusting the distribution of functional fillers in an ideal polymer matrix.However,the study of sub-nanoscopic structure and micro-environment of polymer matrix nanocomposites,and its micro-mechanism between the microstructure and the evolved macroscopic properties are still rarely reported.This paper mainly includes two aspects:First,we prepared environmentally CS/PVA/Fe₃O₄ magnetic nanocomposite membranes,and explored the effects of different composition ratios and the nanoparticle size effects on the microstructure of the nanocomposite membranes.Specifically,the nanofillers were well dispersed in the polymer matrix to improve in its properties.And Fe₃O₄ nanoparticles were used as reinforcing filler,and a mixture of PVA and CS was used as polymer matrix.In order to improve the dispersibility and interfacial adhesion between the nanoparticle and the polymer matrix,the surface of the Fe₃O₄ nanoparticles was modified with polyethylene glycol,and then the hydrophilic magnetic nanoparticles were mechanically converted into magnetic fluid.The PVA/CS composite membranes were prepared at different volume ratios of PVA and CS,and the best mixing ratios of preparing nanocomposite membranes were evaluated by test analysis.The CS/PVA/Fe₃O₄nano-biocomposite membranes doped with different mass fractions were prepared by solution casting method,and various properties of the obtained membranes were characterized.The swelling property of the membranes was examined by evaluating the swellbility.The physical and chemical properties of pure PVA/CS and CS/PVA/Fe₃O₄ membranes were investigated by Fourier transform infrared spectroscopy（FTIR）and X-ray diffraction（XRD）.The effects of doped Fe₃O₄ on the surface and cross-sectional morphology of PVA/CS membranes were investigated by field emission scanning electron microscopy.Finally,the effects of doped Fe₃O₄ on the microstructure of PVA/CS membranes were investigated by positron annihilation lifetime spectroscopy.Second,the magnetic ordered CS/PVA/Fe₃O₄ nanocomposite membranes were prepared by using a magnetic field-assisted solution casting method,and the mechanisms between the microstructure of the nanocomposite membranes and the evolved macroscopic properties（such as optical and magnetic properties）was investigated.Based on traditional characterization methods such as XRD,FT-IR,SEM,UV-vis,and VSM,we combined the positron electron positron lifetime spectroscopy（PALS）to study the microstructure of nanocomposite membranes.PALS is one experimental method of positron annihilation technique,which served as a sensitive probe of studying microstructures.Through positrons implanting into polymeric materials and annihilating directly or converting into positronium with electron,it can offer the sensitive information on free volume properties which based on sub-nano level molecular packing of polymer materials.And we can further understand the influence of the changes in the microstructure of the magnetic ordered nanocomposite membranes on its macroscopic properties and its action mechanism.We believe that the microstructure of the CS/PVA/Fe₃O₄ magnetic nanocomposite membrane changes during the heat-curing process under the external magnetic field,and induces a large number of magnetic nanoparticles in the polymer matrix arranged along the direction of the magnetic induction line.A highly ordered magnetic microstructure with light barrier strip is formed,which effectively enhances the magnetic property and transmittance of the nanocomposite membranes.This work provides experimental basis and guiding significance for designing and preparing new highly ordered magnetically responsive polymer nanocomposites,and provides effective research methods and research ideas for studying the microstructure and macroscopic properties of magnetically responsive polymeric nanocomposites.