Study On The Improvement Of Dielectric Properties Of Polymer-based Nanocomposites And Its Mechanism

Dielectric polymer films have great prospects in the fields of energy storage,electrocaloric refrigeration and pyroelectricity due to their excellent properties.Due to its low dielectric constant,the traditional method to improve the dielectric response of pure polymers is to compound inorganic nano-ceramic materials with high dielectric constant.However,this usually brings some negative effects,such as a significant drop in the breakdown electric field or a significant increase in dielectric loss.In recent years,some studies have found that a small number of nanoparticles with low dielectric constant can also improve the dielectric response of polymers by taking advantage of the particularity of the polymer-nanoparticle interface,and avoid the degradation of other properties.The mechanism of how the interface affects the dielectric properties and the reason of improved dielectric response in nanocomposites remain to be further explored.Based on the problems and analysis above,the research in this paper was focused on the regularity of the improving the dielectric properties in different polymer-nanoparticle composite systems and the mechanism.Chapter 1 mainly introduced the dielectric materials and different dielectric properties,the preparation and application of polymer-based nanocomposites,and the important role of interface in dielectric composites.In chapter 2,the influence of interface on the dielectric response of P?VDF-TRFE-CFE??polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene?composite films and its mechanism were studied.The selected high dielectric constant BaTiO3?Barium Titanate?and low dielectric constant SiO2?Silicon Oxide?nanoparticles both significantly improved the dielectric constant and polarization of P?VDF-TRFE-CFE?at a low volume fraction,it was shown that the improvement of dielectric response was greatly influenced by interface and had little relation with dielectric property of the filler.Further experiments on surface chemical modification of BaTiO3 particles showed that the dipole activity was higher at the interface,which was the important reason for improving the nanocomposites dielectric response.A theoretical model is proposed to explain how the interface affects the dielectric properties of nanocomposites.In chapter 3,the influence of Al₂O₃?Alumina Oxide?nanoparticles with different volume fractions on the dielectric response of PEI?Polyetherimide?/Al₂O₃ composite films and the mechanism were studied.Under low Al₂O₃ volume fraction,interface is thought to be the main reason for improving dielectric response.Under high volume fraction,a large number of Al₂O₃ nanoparticles bring more free volume to linear dielectric polymer PEI,making it easier for some active dipoles to respond under the electric field.In chapter 4,the effect of heat treatment on the dielectric response of PEI nanocomposite films was studied.The dielectric constant of PEI/Al₂O₃ nanocomposite films was improved by special high temperature heating process or air quenching after normal heating process.Chapter 5 was the summary of the whole paper and the prospect.