Design And Preparation Of Polymer-based Functional Composites With Dielectric And Magnetic Properties

With the development of science and technology, the electronic components need to develop to multiple functionalities, miniaturization and light-weight. The new requirement and challenge in material field requires prepare and study the materials with multiple functionalities.Polymer composites have attracted increasing attention in the field of materials due to their excellent physiochemical properties and multiple functionalities. In this work, poly(vinylidene fluoride) (PVDF), polystyrene (PS) and epoxy resin (ER) were used as polymer matrix, iron (Fe), iron oxide (Fe3O4), cobalt ferrite (CoFe2O4) nanoparticles and CoFe2O4 nanofibers were used as magnetic fillers, and carbon nanotubes were used conductive fillers. The polymer composites with dielectric and magnetic properties were prepared by blending methods. The effect of the modification and selective location of fillers, the composition and microstructure of composites, and the conditions of processing on the properties of polymer composites has been systematically investigated. The key information in this work is given as follows:(1) Fe@FexOy nanoparticles with core-shell structure were prepared by using an oxidation process and the Fe@FexOy/ER composites with different filler contents were prepared by solution blend method. The thickness of FexOy shell and the soft magnetic properties of Fe@FexOy could be controlled by adjusting the oxidizing temperature. With increasing oxidizing temperature, the dielectric constant of their ER composites increased because of the improved dispersion of fillers and the enhancement of duplex interfacial polarization. Besides, the real part of the complex magnetic permeability of ER composites had a slight decrease and the breakdown strength of ER composites increased with increasing the oxidizing temperature.(2) CoFe2O4 nanofibers (f-CoFe2O4) were prepared by electrospinning and calcinate process. The microtopography and magnetic properties of f-CoFe2O4 at calcinate temperature of 800℃ and slow heating rate were better than other calcinate conditions. PVDF composite films were prepared with the CoFe2O4 nanoparticles (p-COFe22O4) and f-CoFe2O4 with or without polydopamine modification as fillers, respectively. The experimental results showed the modification treatment and f-CoFe2O4 as fillers were beneficial to improve the dielectric constant in their PVDF composite films. CNT was used as co-fillers and the surface was modified by HNO3 and PDA, and named as a-CNT and CNT@PDA, respectively. The composite films with a fixed content of a-CNT/CNT@PDA as filler and different contents of p-CoFe2O4/f-CoFe2O4 with PDA modification as co-fillers were fabricated. The experimental results indicated the CNT@PDA/f-CoFe2O4@PDA/PVDF composite films with magnetic filler content of 10 wt% had the highest dielectric constant (46 at 100 Hz) than others. The magnetic properties of composite films were influenced by the magnetic properties of p-CoFe2O4 and f-CoFe2O4 fillers. Besides, the addition of magnetic fillers in a-CNT/PVDF and CNT@PDA/PVDF could be restrained the increase of dielectric loss and decreased the degree of crystallinity and melt temperature.(3) The MWCNT and Fe3O4 nanoparticles were modified and used as fillers, the PVDF was used as polymer matrix. The MWCNT/PVDF, Fe3O4/PVDF composite films and pure PVDF with single layer were prepared by solution blend method and the multilayered structure composite films with different arrangements were prepared by hot-pressing. The experimental results showed that good adhesion between the layers after stacking and the layered structure were beneficial to disperse the co-fillers and improve the dielectric constant of composite films, and the interaction among the magnetic fillers and the synergistic effect had affected on magnetic properties of composite films.(4) The PS and PVDF were used as matrix and built the co-continuous structure. The effect of modification of Fe and the selective localization on dielectric and magnetic properties of PS/PVDF composites had been investigated. The results showed the Fe nanoparticles didn’t improve the dielectric constant effectively in their PS/PVDF composites. The CNT was used as co-filler and dispersed in PVDF phase with fixed content in order to increase the dielectric constant. The results showed the selective localization of magnetic filler in PS phase produced a high dielectric constant, and the effect of the selective distribution of the modified Fe nanoparticles (p-Fe) on the dielectric constant was stronger than that of Fe and restrained the increase of dielectric loss. For the magnetic properties, when the filler content was 4 vol%, the composites with the selective dispersion of Fe fillers in PS phase had higher saturation magnetization than others and the difference of real part of the complex magnetic permeability of different composites could be ignored and had low frequency dependence.