Study Of High Dielectric Constant Composites Based On Cyanate Ester Resin

Polymeric composites with high dielectric constant (k) are very important materials for modern industries, which has been one key and hot subject in the field of engineering materials. Ceramic/polymer and conductor/polymer composites are two kinds of high k composites with wide application. However, the optimization on dielectric properties of ceramic/polymer composites based on the"Mixture Rule"is limited; meanwhile, no agreement has been got on dielectric properties and the non-linear enhancement mechanism of conductor/polymer composites. As a result, it is found that the dielectric properties of present composites are grenally not stable. The common issue for all the countries around the world should be addressed is how to prepare dielectric materials with excellent and stable integrated properties.Owing to the importantce of the interface of a composite, this thesis focuses on investigating the interfacial effect on the dieleltric properties of composites. CE resin was used as the matrix, while CaCu₃Ti₄O₁₂ (CCTO) and expanded graphite (EG) sheets were chosen as ceramic and conductor fillers, respectively. Three typical kinds of high k composites including ceramic/polymer, conductor/polymer, and conductor/ceramic/ polymer composites were prepared to investigate the relationship between the interface and dielectric properties, and thus set up a theoretic framework and technique for developing desirable high k composites through controlling the interface nature of composites. This research contains three parts.First, CCTO/CE and CCTO(KH550)/CE composites were prepared, of which CCTO and surface treated CCTO withγ-aminopropyl triethoxy silane (KH550) were chosen as the functional phase, respectively. The chemistry on the surface of CCTO(KH550), and the interfacial effect on dielectric properties of the composites were mainly investigated. Meanwhile, the curing behavior and thermal property of the composites were discussed uning Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and other techniques. Results show that the addition of CCTO and CCTO(KH550) in CE resin can effectively increase the dielectric constant. The composites with stable dielectric properties over a wide frequency and temperature ranges can be prepared by optimizing the structure of the interface. Compared with CE resin, the composites have relatively low curing temperature and better thermal resistance..Second, EG/CE composites were designed and fabricated, of which the non-linear enhancement phenomenan in dielectric properties were intensively studied. Results show that EG/CE composites exhibit low percolation threshold (2.85vol%), where the dielectric constant increases suddenly (the dielectric constant at 1kHz is 100).Third, Three-phase composites (EG/CCTO/CE) composites were prepared, of which the dielectric and electric properties, and the effect of interface on the percolation threshold were studied; moreover, the curing behavior and thermal resistance were also discussed. Results show that three-phase composites have lower percolation threshold (2.75vol%) than EG/CE composites because the former shows better interfacial adhesion than the latter. Meanwhile, the dieledtric constant of three-phase composites is 149 at 1kHz, which is 40 times of that of CE resin. Compared with two-phase composites, three-phase composites exhibit faster curing reactivity and better thermal resistance.The innovation of this reaserch contains two aspects. One is investigating the interfacial effect on the dielectric properties of CCTO/CE composites, the other is discussing the influence of synergy effect on the dielectric properties, and proving that the interface optimization is very important to the enhancement of dielectric properties, meaning that it is possible to develop high-k composites with desirable and stable integrated properties through the control of interface.