Research On Surface Modification Of PVDF-based Polymer Films

Poly(vinylidene fluoride)is a highly promising dielectric material for organic thin film capacitors with high energy storage density.In order to improve its dielectric energy storage properties,researchers have carried out a lot of practical research work and proposed many different modification methods,but all of them have their limitations,regardless of inorganic composite,all-organic composite and multilayer structure design.In this context,the introduction of surface engineering as a modification method to improve the energy storage properties of PVDF and its copolymers has been proposed.In this thesis,PVDF-based polymer films are studied in combination with UV radiation treatment as a surface modification process.The microstructure,surface morphology and energy storage properties of PVDF-based polymer films after UV radiation treatment are systematically investigated.The main work of this thesis is as follows:1.The effects of two different heat treatment processes on the microstructure and energy storage properties of PVDF dielectric films were systematically investigated.Through various characterizations,it was found that the main crystalline phases within the PVDF films were transformed from the originalβ-phase toα-phase when the PVDF films were annealed or quenched,and the crystallinity of the films increased after the heat treatment.These microstructural changes resulted in higher relative permittivity,insulation resistivity and charge/discharge efficiency of the heat-treated PVDF films.2.The effects of UV irradiation process on the energy storage properties of different PVDF film substrates were systematically investigated.The experimental results showed that the relative permittivity and breakdown field strength of the quenched PVDF films were significantly increased after 10 min of UV irradiation treatment at both 185 nm and245 nm bands,and their energy storage density was increased to 13.7 J/cm~3,which was18.6%higher than that before the treatment(11.5 J/cm~3).On this basis,the quenched samples were subjected to UV irradiation for different durations to investigate the optimal UV irradiation treatment time.The quenched PVDF film had the maximum energy storage density(14.2 J/cm~3)at the UV irradiation time of 15 min.3.The effects of different drying temperatures on the microstructure and dielectric properties of polyvinylidene fluoride-hexafluoropropylene films were investigated.With the increase of drying temperature,the content ofα-phase in P(VDF-HFP)films gradually increased,and the crystallinity of dielectric films also gradually became larger.On this basis,the P(VDF-HFP)films dried at 120℃were selected for UV irradiation treatment of different durations.The experimental results showed that the performance of P(VDF-HFP)in UV irradiation was similar to that of PVDF,and the P(VDF-HFP)film dried at120°C had the maximum energy storage density(14.9 J/cm~3)after 10 min of UV irradiation,which was 11.2%higher than that of the original P(VDF-HFP)dielectric film(13.4 J/cm~3).