Huiwu Cai

High dielectric permittivity and low loss in PVDF filled by core-shell Zn@ZnO particles

In this study, metal-semiconductor Zn@ZnO core-shell particles were prepared by the heat treatment of raw Zn powder under air atmosphere, and the prepared Zn@ZnO particles were incorporated into poly(vinylidene fluoride) (PVDF) to obtain high dielectric permittivity polymer. The results indicate that the Zn@ZnO particles remarkably increased the dielectric constant of the PVDF composites compared with the raw Zn/PVDF due to the duplex interfacial polarizations induced by ZnO-Zn interface and ZnO-PVDF interface. Moreover, the dielectric permittivity of the Zn@ZnO/PVDF composites can be further optimized by adjusting the thickness of ZnO shell. The dielectric loss and conductivity were still remained at low acceptable level owing to the presence of ZnO shell between Zn core and PVDF matrix which serves as an interlayer between the Zn cores preventing them from contacting with each other. The developed Zn@ZnO/PVDF polymer composites with high dielectric constant and low loss are potential for embedded capacitor applications.

A Carboxyl-Terminated Polybutadiene Liquid Rubber Modified Epoxy Resin with Enhanced Toughness and Excellent Electrical Properties

The modification of epoxy (EP) resin with carboxyl-terminated polybutadiene (CTPB) liquid rubber was carried out in this work. The chemical reaction between the oxirane ring of EP and the carboxyl group of CTPB and kinetic parameters were investigated by Fourier transform infrared and differential scanning calorimetry. The resulting pre-polymers were cured with methyl hexahydrophthalic anhydride. Scanning electron microscopic observations indicate that the micro-sized CTPB particles dispersed uniformly in the EP matrix formed a two-phase morphology, mainly contributing to the improved toughness of the modified network. The best overall mechanical performance was achieved with 20 phr CTPB; above it, a fall in the strength and modulus was observed. The storage modulus and loss declined with the CTPB concentration due to its lower modulus and plasticizing effect from dynamic mechanical analysis measurements. Moreover, due to the weak polarity and excellent electrical insulation of CTPB, the CTPB-modified EP presented higher electrical resistivities and breakdown strength, and low dielectric permittivity and loss compared with neat EP.

Thermal, mechanical, and dielectric properties of epoxy resin modified using carboxyl-terminated polybutadiene liquid rubber

Epoxy (Ep) resin modified with carboxyl-terminated polybutadiene (CTPB) liquid rubber was investigated in this study. Fourier transform infrared verified the chemical reactions between oxirane ring of Ep and carboxyl groups of CTPB using benzyldimethylamine as a catalyst. The decrease of the thermal stability could be due to the lower thermal stability of CTPB compared with that of pure Ep. The mechanical results showed that CTPB-modified Ep was superior to that of the pure Ep, and the best overall mechanical properties were normally achieved with 20 phr of CTPB content. The impact strength of the system containing 20 phr CTPB increased by 193% due to the two-phase nature of the system. The dielectric constant and dissipation factor of the modified Ep obviously declined with the CTPB content compared with pure Ep, for instance, the dissipation factor remained less than 0.02 in wide frequency range.

Dynamic thermal-dielectric behavior of core-shell–structured aluminum particle-reinforced epoxy composites:

The broadband dielectric spectroscopy was carried out in the frequency range of 1–107 Hz at the −20–200°C range to investigate the effect of temperature on the dynamic thermal–dielectric behavior of the aluminum (Al)/epoxy composite. The epoxy composites with core-shell–structured Al particles were prepared by solution method. The results show that the dielectric permittivity of the composites increased smoothly with a rise of filler content and reduced with an increase in frequency at room temperature. While the dielectric loss and conductivity still remained at low level owing to the nanoscale alumina insulating shell serving as a barrier layer to control the dielectric loss. The dielectric permittivity, dissipation factor, and conductivity of the composites increased with temperature and exhibited an abrupt rise around the glass transition temperature (Tg). A large increase in the dissipation factor and conductivity with temperature is attributed to the direct current conduction of thermal-activated charge carriers resulting from pure epoxy above Tg. The observed temperature-dependent dielectric relaxations of the composites indicated a thermally activated behavior of the relaxation time of epoxy chain segments.

Mechanical and dielectric properties of epoxy composites filled with hybrid aluminum particles with binary size distribution

Epoxy composites incorporated with three kinds of hybrid aluminum (Al) particles with binary size distribution, that is, [1 μm/45 μm], [1 μm/18 μm], and [18 μm/45 μm], respectively, were prepared, and the mechanical and dielectric properties of the hybrid Al/epoxy composites were investigated as a function of relative weight fraction of smaller-size Al (Ws) of hybrid Al particles at a total filler content of 50 wt%. The mechanical and electrical properties of the hybrid Al/epoxy composites are found to mainly depend on the type of hybrid filler and the Ws and can be tuned by changing the Ws. The maximum tensile strength and elongation at break of the composites appear at an optimal Ws. Furthermore, the dielectric permittivity, dielectric breakdown strength, and volume resistivity of the hybrid Al/epoxy composites also exhibit the similar variations as the mechanical properties with the Ws. The obvious enhancements in the physical properties can be ascribed to the synergistic effect of hybrid particles in the matrix at the optimal Ws, which endows the composites with better mechanical and dielectric properties. So, the results give a facile strategy to enhance the dielectric and mechanical properties of the composites by choosing a proper Ws at a fixed total filler loading.