Study On The Dielectric Properties Of Modified Nano Silver/Ceramic /PVDF Composites

With further research of nanocomposites, filler powder in high dielectric polymer matrix composite has fine particles to the nanometer size range, the relatively low dielectric properties of the conventional ceramic/polymer composites limits its application in the field of electrical, communications and electronic information. According to the percolation theory, The dielectric properties of polymer could be increased dramatically by the introduction of nano conductive fillers. Improvement in dielectric properties is expected when a polymer is mixed with metal nanoparticles and ceramic, and the surface of inorganic fillers have been modified. In this paper, Ag nanoparticles would be introduced and modified in the ceramic/polymer composites, we would use the method of ceramic surface chelate modification to improve the interface connection of composites, modified Ag/modified BT/PVDF three-phase composites would be prepared.In order to get more excellent dielectric properties of three-phase composites, in this paper, the experiments by the following aspects have been shown that:1、By using the liquid phase reduction method, modified nano-silver is prepared in the cysteine solution. PVDF and Ag were selected as the matrix polymer and conductive filler, respectively, Ag nanoparticles(AgNPs) and cysteine-capped AgNPs are synthesized successively.Ag/PVDF composites are prepared by melt blending. the structural and surface property of unmodified Ag/PVDF and modified Ag/PVDF composites were investigated and the dielectric properties of composites are determined.Results show that the dielectric constant of modified Ag/PVDF composites increased with the increase of the volume fraction of Ag phase, and the dielectric loss also increased through the electric resistance test. when the volume fraction of unmodified Ag was 18%, dielectric constant of the composites reached maxmum point 57.5(100Hz), at the same time, the volume fraction of unmodified Ag was 24%, dielectric constant of the composites was 194, there is no percolation in the nanocomposites.2、By solution blending method, ceramic surface chelate modification by the cysteine –capped silver nanoparticles is prepared, the surface of modified BT ceramics have combined with a layer of chelating layer and sulphur modified silver nanoparticles also attached on the surface, the function of the whole system have formed. Modified Ag/ BT/PVDF composites are prepared by hot-pressing method, the influence of modified Ag volume fraction on the dielectric properties of composite materials was studied, and the effects of interfacial modification on dielectric properties of the system were analyzed. when the volume fraction of modified Ag was 20%, BT:PVDF=7:3, dielectric constant of the composites reached 1355, dielectric loss was 0.32, The composite closed the percolation threshold. when the volume fraction of modified Ag was 20%, BT:PVDF=6:4, dielectric constant of the composites reached 870, dielectric loss was 0.177. Relative content of ceramic and silver nanoparticles in three-phase composite materials has an important influence on dielectric properties, especially the interface polarization and percolation threshold phenomenon.3、By solution blending method, modified Ag/modified BT/PVDF composites are prepared by the introduction of tartaric acid modified BT in the cysteine-capped Ag solution. To the test, results show that the dielectric constant increased with the increase of the volume fraction of ceramic phase when the system content of modified Ag in a certain, and when BT and PVDF have a fixed ratio, the dielectric constant of modified Ag/modified BT/PVDF composites greatly increased with the increase of the volume fraction of Ag phase. When the volume fraction of modified Ag was 25%, BT:PVDF=7:3, dielectric constant of the composites reached 857, dielectric loss was 0.14. When the volume fraction of modified Ag was 25%, BT:PVDF=6:4, dielectric constant of the composites reached 327, dielectric loss was 0.1, the dielectric properties of the composite material is excellent and stable, so the composite material is more practical application value. When the volume fraction of PVDF was 40%,the dielectric constant of the composite slowly increased with the increasing of silver nanoparticles, dielectric loss at this time mostly was 0.1. the experimental results show that the double modification of inorganic phase raised its in the dispersion of the composites and improved the interfacial compatibility between inorganic and organic phase, then enhanced the dielectric properties of the composites.