Preparation And Dielectric Properties Of Multidimensional Ag/based Nanoparticles/Polyvinylidene Fluoride Composites

With the rapid development of electronic products,the functionalization and miniaturization of energy storage dielectric materials have become the development trend of advanced electronic materials.Flexible dielectric energy storage materials have received widespread attention due to their advantages such as good processability,lightweight,fast charge and discharge rate,and high energy storage density.In a single nanoparticle modified polymer-based flexible dielectric material,there are problems such as poor filler dispersion,the easy formation of conductive paths,and large energy loss during charge and discharge cycles between the matrix and the filler.For this reason,surface modification of nanoparticles has become an effective means of modification.In this paper,nano-silver(Ag)is used as functional nanoparticles.Through different surface modification methods,a series of one-dimensional and two-dimensional hybrid particles are synthesized,and then they are doped into a PVDF matrix with good ferroelectric properties to prepare PVDF-based nano-particles.Explore the effects of hybrid particles with different dimensions and different morphologies on the microstructure and dielectric properties of PVDF-based composites.The first part of this paper studies the influence of one-dimensional core-shell nanorods with inorganic insulator Al₂O₃,inorganic semiconductor Zn O and organic semiconductor PDA as the shell and Ag nanorods as the core on the dielectric properties of PVDF-based composites.Through microscopic characterization,it is found that controlling the reaction conditions can form three shell structures with a thickness of about 35 nm on the outside of the one-dimensional Ag rod.The core-shell nanorods have good dispersibility in the PVDF matrix,and the organic layer coating shows better compatibility with the PVDF matrix than the inorganic layer coating.XRD and FT-IR analysis showed that the core-shell nanorods can effectively induce the transformation of PVDF crystalline phase from?phase to more polar?and?phases.The dielectric performance test results show that the one-dimensional core-shell nanorod/PVDF composites generally exhibits a relatively high dielectric constant and relatively low dielectric loss.Under an electric field of 1800 k V/cm,the discharge energy density of the Ag@Zn O/PVDF composite reaches 4.02 J/cm³.This is because Ag nanorods have a strong electronic polarization effect.The one-dimensional core-shell nanorods coated with semiconductors can also make the composite have higher polarization capabilities.At the same time,the inorganic shell structure can help the material to resist higher The breakdown voltage of the inorganic semiconductor coating material Ag@Zn O/PVDF is more outstanding in dielectric properties.Then,the author builds a two-dimensional structure with the help of a metal organic framework(MOF)to prepare two-dimensional hybrid nanosheets coated with monometallic Ni MOF and bimetallic Ni Fe MOF,and systematically study the effect of two-dimensional hybrid nanosheets on PVDF The influence of matrix composite on the dielectric properties.The microstructure analysis results show that Ag particles are uniformly dispersed inside the MOF nanosheets,and at low mass concentrations(?15 wt.%),the content of Ag particles shows a certain controllability.The dielectric test results of the composite show that when the content of Ag/Ni Fe MOF in PVDF is 10 wt.%,the electric displacement of the composite is 11.11?C/cm²,and the discharge energy density of the composite under an electric field of 2500 k V/cm is 8.01 J/cm³.This is because the introduction of nano-Ag particles can significantly increase the total number of electrons in hybrid MOF nanosheets and enhance electronic polarization.At the same time,Ni Fe MOF has a higher electric dipole moment,thereby improving the polarization ability of the composite.In addition,the MOF nanosheets coordinated by Ni Fe atoms can effectively increase the space charge mobility in the interface between the filler and the matrix,and reduce the space charge concentration.The Coulomb blocking effect generated by the Ag nanoparticles under the action of high electric field strength can also inhibit electrons.This compound effect greatly increases the voltage strength of the composite.Therefore,the Ag/Ni Fe MOF/PVDF composite exhibits better dielectric properties.Based on the above results,finite element simulations were carried out on the polarization and dielectric properties of the multilayer composite.The simulation results show that the design of the multilayer structure can significantly suppress the distortion of the electric field,thereby greatly increasing the breakdown field strength of the composite.Under the same particle concentration,with the increase of the number of layers,the polarization strength of the multilayer composite and the breakdown field strength both increase first and then decrease;when the multilayer structure is seven layers,the theoretical energy storage density of the composite reaches the maximum.The Ag/Ni Fe MOF/PVDF multilayer composite with a total content of 10 wt.%nanoparticles was prepared,and the dielectric performance test,the change law of the energy storage density are consistent with the simulation results.When the multilayer structure is seven layers,the dielectric constant and breakdown field strength of the composite are 16.76 and 2850 k V/cm,respectively,and the energy storage density increases from 8.01 J/cm³in a single layer to 9.467 J/cm³.In summary,this thesis comprehensively explores the influence of different dimensions of nanoparticles and layered structure on the dielectric properties of PVDF matrix,and systematically studies the influence of filler dimensions and macro material structure on the energy storage characteristics of PVDF-based composite.The results show that with the introduction of nano-dimensions and macroscopic multilayers of composite materials,the polarization ability,breakdown voltage,and discharge density of composite show a gradual upward trend,which provides a certain theoretical and experimental reference for subsequent research on nano-dielectric materials.