Preparation And Performance Study Of Polyvinylidene Fluoride Nanofiber-based Dielectric Composites

The preparation methods of polyvinylidene fluoride(PVDF)and its copolymer-based composite dielectric films are currently based on solution flow-delaying,which has problems such as low preparation efficiency and low percentage of polar phases in dielectric films.In this paper,a solution jet spinning process was used to fabricate polyvinylidene fluoride nanofiber-based dielectric composites,which is simple,stable,efficient,continuous,safe,and has some prospects for industrial applications.The prepared PVDF-based dielectric films have a higher polar phase ratio and better dielectric properties compared with the solution flow-delay method.In this thesis,the process of PVDF-based composite dielectric films and their dielectric properties are discussed in depth,aiming to explore the preparation of polyvinylidene fluoride nanofiber-based composite films by solution spray spinning process,which improves the dielectric properties of PVDF-based composite dielectric films while increasing the processing efficiency.Firstly,pure polyvinylidene fluoride(PVDF)nanofiber films were prepared by solution spray spinning(SBS)technology,and their dielectric properties were investigated.The results showed that the PVDF fiber film has high dielectric constant and low loss angle tangent,which makes it a promising dielectric material for potential applications.It was also found that the polar phase content of PVDF membrane can be increased by SBS and cold-press annealing processes to significantly improve its dielectric properties,and the SBS process has the advantages of safety,efficiency and energy saving compared with the traditional electrostatic spinning.Next,polyvinylidene fluoride(PVDF)/polyethylene glycol(PEG)composite membranes were prepared,and their dielectric properties and thermal response properties were investigated.The results showed that the composite film had significant dielectric pulse characteristics with the amplitude of dielectric pulse and dielectric switching rate reaching 287.9 and 32.6,respectively.It was also found that the interaction between PVDF and PEG had a great influence on the dielectric behavior of the composite,and the increase of PVDF polar phase content had a positive effect on its dielectric pulse behavior.Finally,PVDF/PANI nanofiber composite films were prepared by SBS process by doping PANI nanofibers into PVDF matrix,and it was found that both SBS process and homogeneous dispersion of PANI nanofibers helped to significantly improve the dielectric constant and effectively suppress the dielectric loss.The polar content of PVDF/PANI films exceeded about 71% at room temperature,and the homogeneous mixing of PANI nanofibers and PVDF and the good interfacial properties between PVDF matrix and PANI nanofibers resulted in the excellent dielectric and mechanical properties of the fiber composite films.In summary,the preparation of PVDF-based composite dielectric films by SBS can optimize the crystal structure and dielectric properties of the material while obtaining high processing efficiency.Due to the advantages of continuous,safe,efficient and low-cost SBS process,it has certain prospects for industrial applications.