Controllable Fabrication And Property Regulation Of Polymer Nanocomposites With High Dielectric Constant And Low Dielectric Loss

Polymer nanocomposite dielectric materials with high dielectric constant, low dielectric loss and high energy density have huge potential applications in modern electronic and electrical equipment. The research and development of high performance polymer nanocomposite dielectric materials are of significant importance for the economy and security of the national. Recently, a lot of contributions and efforts have been paid to improve the integrated performance of polymer nanocomposite dielectric materials. However, there are still many problems to be solved, such as the dispersion of nanofillers, the interface between nanofillers and polymer matrix, and the high filling quantity etc. In order to solve these problems, in this dissereation, a series of simple, rapid, efficient and controllable methods were explored to prepare surface modified nanofillers. By design and synthesis of different interface structure, the effects of interface structure on the dielectric properties of polymer nanocomposite dielectric materials were systematicly studied, and on this basis, polymer nanocomposite dielectric materials with excellent dielectric properties were successfully prepared.Firstly, in order to improve the dispersion of nanoparticles and interfacial compatibility between the nano fillers and polymer matrix, "Grafting from" and "Grafting to" strategis were adopted, by in situ initiated RAFT polymerization and "Thiol-Ene" click reaction, a series of core-shell structure of Polymer@BT nanocomposite dielectric materials were prepared. In these materials, the insulating polymer shells not only act as interlayers to prevent the agglomeration of the nanoparticles, but also can be used as the polymer matrix. Polymer matrixes are directly connected with the nanofillers by covalent bonds, so the interface structure of the polymer nanocomposites are very compact. In this part, the surface modification of nanoparticles were characterized by FT-IR, 1H NMR, TGA, TEM, dynamic light scattering and other testing methods, the results demonstrated that the core-shell structured Polymer@BT nanoparticles were successfully prepared. Moreover, the composition and/or grafting density of the polymer nanocomposites were regulated by adjusting the feed ratios of the monomer or molecular weight of the grafting polymer. The effects of interface structure on the electrical properties of polymer nanocomposite dielectric materials were also systematicly studied.Secondly, in order to further improve the dielectric properties, we developed a novel strategy to improve the interface between the high dielectric constant nanoparticles(i.e., Ba TiO3, BT) and ferroelectric polymer [i.e., poly(vinylidene fluoride-co-hexafluoro propylene)]. Core-shell structured Ba TiO3 nanoparticles either with different shell thickness or with different molecular structure of the shell were prepared by grafting two types of fluoroalkyl acrylate monomers via surface- initiated reversible addition fragmentation chain transfer(RAFT) polymerization. The dielectric properties and energy storage capability of the corresponding nanocomposites were investigated by broadband dielectric spectroscopy and electric displacement-electric field loop measurement, respectively. The results show that high energy density and low dielectric loss are successfully realized in the nanocomposites. Moreover, the energy storage densities of the P(VDF-HFP)-based nanocomposites could be tailored by adjusting the structure and thickness of the fluoro-polymer shel.Thirdly, in order to reduce the dielectric loss, enhance the breakdown strength and energy density of polymer nanocomposites, we designed and synthesized strawberry core-shell structured BT-PDA-Ag nanoparticles, and prepared P(VDF-HFP) based polymer nanocomposite dielectric materials by solution blending and hot pressing. A layer of polydopamine(PDA) shell was coated on the surface of BT nanoparticles by the self polymerization of dopamine. And then, the Ag nanoparticles were embedded into the shell via in situ reduction. Utilizing the coulomb blockade effect of Ag nanoparticles, we successfully inhibited the leakage current, decreased the dielectric loss, and enhanced the breakdown strength and energy density of the polymer nanocomposites.Lastly, in order to reduce the content of fillers, and prepare polymer nanocomposite dielectric materials which can be used in small, lightweight and flexib le electrical and electronic equipment, polydopamine coated RGO(PDA-RGO) and fluoro-polymer functionalized RGO(PF-PDA-RGO) were prepared by a facile and environmental friendly approach. The corrosponding P(VDF-HFP) based polymer nanocomposite dielectric materials were prepared by solution blending and hot pressing. Compared with unmodified RGO, the resulting PF-PDA-RGO nanosheets exhibited excellent dispersion in ferroelectric polymer matrix and strong interfacial adhesion with the matrix, leading to a low percolation threshold(=1.06 v%) and excellent flexibility for the corresponding nanocomposites. The results show that the P(VDF-HFP)/PF-PDA-RGO nanocomposites have a relatively high dielectric constant, and maintain low dielectric loss and excellent flexility. Our strategy provides a new pathway to prepare high performance flexible nanodielectric materials.