| In recent years,the electronic and electrical industry has ushered in a period of rapid development.The miniaturization,lightweight and high integration of electronic components have set higher demands on the integrative performance of materials.Among various materials,dielectric polymer nanocomposites have received more and more attention due to their great potential application prospects.Although much efforts have been made to improve the integrative performance of polymer nanocomposites,there are still some issues to be addressed,for example,the rational selection of nano fillers,the dispersion of nanofillers in the polymer matrix,and the effect of interface on the properties of the nanocomposites.In this thesis,the effect of different one-dimensional nanofillers on the electrical performance of nanocomposites was investigated.Then,the simple modification method was employed to functionalize the nanofillers to improve the compatibility between the nanofillers and polymer matrix.Besides,the effects of different interface structures on the electrical properties of polymer nanocomposites were also systematically studied.Firstly,in order to investigate the effect of one-dimensional nanofillers with different intrinsic properties on the electrical performance of nanocomposites,the high-dielectric-constant polymer nanocomposites were fabricated based on four kinds of nanowires(NWs)prepared by hydrothermal and high-temperature calcination.The results demonstrated that the nanocomposites comprising BaTiO3 NWs possessed higher dielectric constant than the other nanocomposites,while the incorporation of TiO2 NWs gave the nanocomposites the highest breakdown strength.Benefiting from the anisotropy of nanowires,low dosage of nanowires might be conducive to the increase of breakdown strength for these composites.Compared with the pure polymer,the addition of nanowires gave rise to significantly enhanced energy storage capability of nanocomposites.The nanocomposites with BaTiO3 NWs possessed the highest total stored and discharged energy densities,while the energy storage efficiency of the nanocomposites with TiO2 NWs was the highest.This work provides deep insights into the influence of different kinds of nanowires on the dielectric performance and energy storage capability of polymer nanocomposites.In addition,the results also pave the way for the further preparation of nanocomposites with high energy density.Secondly,two kinds of dopamine derivatives with long-chain tail,h-DOPA and f-DOPA,were designed and synthesized to improve the compatibility between the one-dimensional nano filler and polymer matrix.Based on the facile oxidative self-polymerization of dopamine,TiO2 and BaTiO3 NWs were successfully coated with polydopamine,respectively.By employing more advanced film casting method,high-performance polymer nanocomposites were then fabricated.Due to the successful deposition of polydopamine on the surface of nanowires,dielectric loss,leakage current and remnant polarization of thus-fabricated nanocomposites were remarkably suppressed,while the energy density was greatly improved.For example,the nanocomposites comprising f-DOPA@TiO2 and f-DOPA@BaTiO3 NWs discharged ultrahigh energy densities of 11.48 J cm-3 and 12.87 J cm-3,respectively,much higher than that of commercial BOPP 3.56 J cm-3,also comparable to those of previous fabricated dielectric materials,showing their broad application prospects.The coating of f-DOPA was better than that of h-DOPA on the basis of the property comparison between the nano wires modified with these two kinds of dopamine derivates.The facile,efficient and universal surface modification with dopamine derivatives could be used to functionalize various types of inorganic materials.The results might provide an effective method to enhance the energy density of dielectric polymer nanocomposites through rational selection and elaborative functionalization of nano fillers.Then,in order to alleviate the highly inhomogeneous electric fields stemmed from the large contrast in the dielectric constant between the nanofiller and the polymer matrix,the core-shell structured mTiO2@BaTiO3 NWs with various thickness of TiO2 shell layers were designed and synthesized to fabricate high-dielectric-constant polymer nanocomposites.The introduction of TiO2 with moderate dielectric constant between BaTiO3 NWs and the polymer matrix gave rise to the gradient of the dielectric constant,which effectively alleviated the undesirable electric field concentration and suppressed the sharp decrease of breakdown strength.Benefiting from the TiO2 shell layer,the dielectric loss,leakage current and remnant polarization of the nanocomposites,as well as the decrease of charge-discharge efficiency,were significantly reduced.For example,the nanocomposites could still possess the high efficiency of?60%even at the highest loading of dopant(20 wt%).The finite element analysis further confirmed the outstanding properties of nanocomposites by the utilization of TiO2 shell layer coated BaTiO3 NWs.It is worth noting that the intrinsic semiconductive characteristic of TiO2 would hamper the performance of the nanocomposites with thicker TiO2 shell layers,resulting in higher leakage current density and dielectric loss,which is not conducive to the substantial enhancement of energy storage capability of nanocompo sitesFinally,in order to suppress the adverse effect of the semiconductor properties of TiO2 on the electrical performance of the nanocomposites,BaTiO3 nanoparticles coated TiO2 NWs were designed to prepare dielectric polymer nanocomposites.Due to enhanced interfacial polarization resulted from the special core-shell structure of BaTiO3@TiO2 NWs,the dielectric constant of nanocomposites comprising BaTiO3@TiO2 NWs was higher than that of nanocomposites with pristine TiO2 or BaTiO3 NWs.Meanwhile,the coating of BaTiO3 on the surface of TiO2 NWs brought about the suppression of leakage current,dielectric loss and remnant polarization of nanocomposites,which was beneficial for the maintenance of breakdown strength Those features finally led to high energy storage capability of nanocomposites.The work indicates that different interface structures could have a significant effect on the electrical performance of polymer nanocomposites.The control of interface structure is of great importance for the construction of high-energy-density polymer nanocomposite. |
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