Dielectric Properties Of Polyvinylidene Fluoride Composites Co-modified By Low-dimensional Carbon Materials And Boron Nitride

With the development of the electronics industry,dielectric materials are required to have higher dielectric constants and lower dielectric losses.The traditional ceramic material has a very high dielectric constant,however,the preparation process is complex,brittle,and the processing temperature is high.Organic polymers have good flexibility,low dielectric loss,and easy processing,but the dielectric constant is low.Therefore,the preparation of polymer-based composite materials with high dielectric properties is of great significance.In this paper,different types of dielectric composites were prepared by the method of solution blending,and the micromorphology,structure and conductivity of these composites were investigated by scanning electron microscope（SEM）,X-ray diffraction（XRD）and broadband dielectric and impedance spectroscopy.And dielectric properties are tested and characterized to find the best filler ratio and composites with the best dielectric properties.The details are as follows:（1）BN/PVDF,MWCNT/PVDF and GR/PVDF two-phase composite materials were prepared by the solution blending method,with BN,MWCNT,and graphene（GR）as fillers,and polyvinylidene fluoride（PVDF）as the polymer matrix.The results show that the method of ultrasonic dispersion can make the filler evenly dispersed in PVDF.The BN filler has a promoting effect on the formation of theαcrystal form of PVDF,and MWCNT and GR have little effect on the formation of the PVDF crystal form.BN can slightly improve the dielectric constant of the composite material,but the conductivity and dielectric loss have not changed significantly;when the filler MWCNT or GR reaches a certain mass fraction,the conductivity,dielectric constant and dielectric loss of the composite material will have very obvious improvement.When the frequency is 10²Hz,the mass fraction of MWCNT is 0.75%and 1%,the conductivity of MWCNT/PVDF is 1.6×10^-8S/m and 1.6×10^-6S/m,respectively,the dielectric constant is 122.8 and 414.6,the dielectric loss is 2.28 and 64.98 respectively;when the GR mass fraction is 3%and 4%,the conductivity of GR/PVDF is 6.8×10^-8S/m and1.6×10^-7S/m,respectively.The dielectric constants are 267.7 and 539.0,and the dielectric losses are 4.28 and 5.07,respectively.（2）MWCNT/BN/PVDF and GR/BN/PVDF three-phase composites were prepared by the solution blending method with MWCNT and BN or GR and BN as fillers and PVDF as the polymer matrix,respectively.The results show that BN can be evenly dispersed between MWCNT and GR,and the three-phase composite material can keep the dielectric loss at a low level while maintaining a high dielectric constant.When the BN mass fraction is 4%and the MWCNT mass fraction is 1%and 0.75%,the dielectric constant of the MWCNT/BN/PVDF three-phase composite at 10²Hz can reach 229.72 and 49.26,and the dielectric loss is 5.92and 0.086.When the BN mass fraction is 4%and the GR mass fraction is 4%and 3%,the dielectric constant of GR/4%BN/PVDF three-phase composite material at 10²Hz can reach144.5 and 132.2,and the dielectric loss is 1.09 and 0.52,respectively.（3）ABA-type MWCNT/PVDF-BN/PVDF-MWCNT/PVDF and GR/PVDF-BN/PVDF-GR/PVDF layered composites were prepared by solution blending and hot-press molding methods,using MWCNT and BN or GR and BN as fillers and PVDF as the polymer matrix,respectively.The results show that there is a clear interface in the layered composite material,and the layered composite material also increases the dielectric constant of the composite material while maintaining a low dielectric loss.When the frequency is 10²Hz,the dielectric constant of the ABA type 1%MWCNT/PVDF-4%BN-1%MWCNT/PVDF layered composites can reach 48.8,while the dielectric loss is 1.1.The dielectric constant of 4%GR/PVDF-4%BN-4%GR/PVDF layered composites is 322.2,while the dielectric loss is only 1.38.