Polymeric Matrix Composites With High Dielectric Constant

High dielectric constant material is an insulation material with very broad application prospects in many fields such as electrical and cable industries, so it is important to enhance its dielectric constant. High dielectric constant polymeric matrix composites with advantages of light weight, easy processing, low cost and good mechanical properties, have caught worldwide attention. In the existing systems of high dielectric constant polymeric matrix composites, comparing to the two-phase ceramic/polymer composites and conductor/polymer composites, the three-phase conductor/ceramic/polymer composites have higher dielectric constant. Therefore, the study in the three-phase conductor/ceramic/polymer composite is of great practical significance.At present the conductor of such complex systems are mostly inorganic materials such as metals, graphite and carbon nanotubes. It is rare to use conductive polymer as a conductor like conducting polyaniline (PANI). In aspects of preparing the composites, most of the studies took the traditional mechanical mixing and solution blending method, while the in-situ polymerization technique was rarely reported.In this thesis, by the technique of in-situ polymerization, a series of conductor (PANI)/ceramic (BaTiO₃) binary composites were prepared as intermediates, then a conductor (PANI)/ceramic (CCTO)/polymer (Epoxy resin) three-phase composite was prepared taking epoxy resin (Epoxy) as substrate. The morphology, electrical properties, dielectric properties and thermal properties of the two series of composites were studied to provide theoretical and experimental basis for application of these new polymer matrix composites.Two kinds of PANI/BaTiO₃ composites (coded as PANI(HCl)/BaTiO₃ and PANI(DBSA)/BaTiO₃) were synthesized by in-situ polymerization technique, in which PANI was doped with hydrochloride acid (HCl) or dodecylbenzene sulfonic acid (DBSA). The structure, morphology, thermal resistance, AC conductivity and dielectric ?properties of the composites were evaluated. Results show that the two kinds of composites have core-shell structure, in addition, comparing to PANI(HCl)/BaTiO₃, PANI(DBSA)/BaTiO₃ has better thermal stability, higher AC conductivity and dielectric constant.A series of PANI/CCTO/Epoxy composites were prepared by in-situ polymerization. The curing behaviors of epoxy resin, CCTO/Epoxy and PANI/CCTO/Epoxy composites were studied. Gel time and DSC analyses show that the addition of CCTO and PANI/CCTO into epoxy reduces the curing rate of epoxy. SEM studies show that the CCTO and PANI fillers have good dispersion and compatibility with epoxy matrix. The thermal properties of the composites were studied by DMA and TG analysis. DMA analyses shows that the addition of CCTO and PANI/CCTO into epoxy slightly decreases the glass transition temperature (Tg). TG studies show CCTO(K) 20%/Epoxy has better thermal stability than PANI5%/CCTO(K) 20%/epoxy, and both of them have better thermal resistance than epoxy resin. AC conductivity and dielectric properties of the composite were studied by broadband dielectric spectroscopy. The results show that the percolation threshold of PANIm/CCTO(K)20%/Epoxy composites was about 0.06, and a significant mutation of AC conductivity, dielectric constant and loss appears near the percolation threshold. When the content of PANI is lower than the percolation threshold, the dielectric constant of the composites changes little with the increase of the test frequency, however, when the content of PANI is more than the percolation threshold, the dielectric constant of the composite increases rapidly with the increase of PANI content and decreases quickly with the increase of the test frequency. Under the condition of 1KHz at room temperature, PANI10%/CCTO(K)20%/Epoxy composite has the highest dielectric constant of 220, which increased 62 times than epoxy resin.