Preparation And Properties Of Graphite Nanosheets/Polyvinylidene Fluoride Dielectric Functional Composite Films

With the rapid development of the information,electronics,and power industries,the production of polymer-based composite materials with high dielectric constant and low dielectric loss at low cost has become a hot topic in the industry.In the field of electrical engineering,such polymer-based composite materials can be used as dielectric materials for high-energy-density capacitors;in the field of microelectronics,by selecting a suitable polymer matrix,large-capacity embedded microcapacitors can be prepared on a large scale,thereby ensure high-speed and safe operation of integrated circuits.Compared with other polymers,polyvinylidene fluoride(PVDF)has outstanding electrical properties,good chemical resistance,high temperature resistance,piezoelectricity,and small electromechanical coupling coefficient,so it is often to be used as the matrix to prepare dielectric composites by filler modification or blend modification.In this paper,three kinds of coupling agents with different polarities of the terminal groups(ordered by the polarity of terminal groups of the coupling agents,PFOES>KH550>KH570)were used to modify the graphite nanosheets(GNs).Then these modified GNs were doped into PVDF to prepare composite films.The structure and properties of the composite film were characterized and tested,and the effects of the content of graphite nanosheets and different end-group coupling agents on the structure and properties of the composite film were discussed.XRD results show that the introduction of graphite nanosheets promote the PVDF film from multi-phase coexistence to a phase with excellent ferroelectric properties.Broadband dielectric spectroscopy analysis results show that the dielectric constant of the composite film is positively related to the graphite nanosheets content.Under the test conditions of 100 Hz,when the graphite nanosheets content is 3 wt%,the dielectric constant of the composite film reaches to 138,which obviously increases.When the GNs content is 5 wt%,the dielectric constant of the composite film reaches 287.For KH570,KH550and PFOES modified GNs/PVDF composite films,when the GNs content is 3wt%,the dielectric constants of the composite films reach 85,112 and 298,all of which increase significantly.When the GNs content is 5 wt%,the dielectric constant of the composite film reaches 302,263,and 335.Modified GNs/PVDF composite film with different coupling agents.Under the test conditions of 10~4Hz,When the GNs content is 5 wt%,the dielectric loss of the composite film decreased from 5×10~2(GNs/PVDF)to 0.2(KH570),0.3(KH550)and 0.9(PFOES).The breakdown field strength of the composite film modified with the coupling agent was also improved.Comparing the breakdown field strength values of pure PVDF films(20.42 k V/mm),the breakdown field strengths of composite films with graphite nanosheets content of 5 wt%are 85.39 k V/mm(KH570)and 83.59k V/mm(KH550)and 69.8 k V/mm(PFOES).Based on the above electrical performance test results,the pure PVDF energy storage density was calculated to be 0.01965.The energy storage densities of composite films with a graphite nanosheets content of 5 wt%are 0.10145 J/cm~3(unmodified),5.73246J/cm~3(KH570),5.73246 J/cm~3(KH550),6.13691 J/cm~3(PFOES).A comprehensive comparison of various properties of the composite film after adding the modified graphite nanosheets found that the stronger the coupling agent's polarity for the dielectric constant of the composite film,the better the enhancement effect.For the composite film breakdown field strength,the weaker the coupling agent's polarity,the better the breakdown field strength enhancement effect.The main reason is that the polarity of the coupling agent's end group enhances the polarization effect of PVDF,so the electrical properties will change correspondingly to the strength of the coupling agent.