Zhimin Dang

Dielectric behavior of three-phase percolative Ni–BaTiO3/polyvinylidene fluoride composites

A three-phase percolative composite with a ferroelectric phase (BaTiO3) and metallic inclusions (Ni) embedded into polyvinylidene fluoride matrix was prepared by using a simple blending and hot-molding technique. Effective medium approximations and percolation theory were employed in order to design and describe the dielectric behavior of such three-phase composites. Our experimental results showed that the static dielectric constant of such a three-phase composite can reach above 800 when the Ni concentration is close to its percolation threshold. Such composites have a potential to become capacitors and can be easily fabricated into various shapes due to its flexibility.

Thermal, electrical and mechanical properties of plasticized polymer electrolytes based on PEO/P(VDF-HFP) blends

Abstract The polymer electrolytes composed of a blend of poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as a host polymer, mixture of ethylene carbonate (EC) and propylene carbonate (PC) as a plasticizer, and LiClO 4 as a salt were prepared by a solution casting technique. SEM micrographs show that P(VDF-HFP) is very compatible with PEO. The ionic conductivity of the electrolytes increases with increasing plasticizer content, while the mechanical properties become obviously worse. By addition of a certain content of PEO in P(VDF-HFP) matrix, a good compromise between high ionic conductivity and mechanical stability can be obtained.

Dielectric behavior of novel three-phase MWNTs/BaTiO3/PVDF composites

Abstract A three-phase composite with multi-walled carbon nanotubes (MWNTs) and BaTiO 3 particles embedded into polyvinylidene fluoride was prepared by using a simple blending and hot-molding technique. The dielectric measurement results show that the effective dielectric constant of the composite is slightly dependence on the frequency below 1 MHz but increases rapidly with the MWNTs concentration when the concentration is very close to the percolation threshold. The temperature has a little effect on the variation of the dielectric behavior. The percolation theory is used to explain the experimental results.

Dielectric behavior of Li and Ti co-doped NiO/PVDF composites

Abstract The dielectric behavior of two kinds of Li and Ti co-doped NiO (LTNO)/polyvinylidene fluoride (PVDF) composite was studied at various different frequencies and temperatures. The effective dielectric constant of the percolative composite at 100 Hz is very high, i.e., e eff ≈600, which is 60 times higher than that of the PVDF. The results also show that there is a remarkable difference in the dielectric constant of the composites with different LTNO fillers. Boundary layer capacitor effect and percolation theory can be used to explain the experimental results.

Dielectric properties of carbon fiber filled low-density polyethylene

Carbon fiber (CF) filled low-density polyethylene (LDPE) matrix composites was prepared by means of the Hakke driver. The dielectric properties of the CF/LDPE composites as a function of the frequency and the volume fraction of CF were studied. The dielectric constants decrease slowly with increasing the frequency and rise gradually with increasing the CF contents in the composites. As the volume fraction of the CF is up to 0.20, an abrupt increase in the dielectric constant occurs, and accordingly electrical conductivity measured at low frequency increases rapidly at this volume fraction. The percolation theory and the simple concept of polarization in the capacitors are employed to explain these experimental results.

Preparation of nanosized ZnO and dielectric properties of composites filled with nanosized ZnO

Abstract Nanosized ZnO powder is prepared by a precipitation method that is simple, convenient manipulation and low energy consumption. The process can produce white ZnO powder of 50–90 nm in size. The dielectric constants of composites with nanosized ZnO filler are also studied in detail in a frequency range of 1–10 MHz by an impedance analyzer. Composites with more ZnO filler have relatively large dielectric constants and losses and they increase with increasing the frequency. High frequency has a remarkable effect on dielectric constants and losses of the composites. Finally, the high dielectric constants and losses of the composites appear under 10 MHz in experimental study. In addition, mixing temperature and time also play an important role on dielectric constants and losses. High temperature and long time during the mixing process might induce the structure change of low-density polyethylene (LDPE). Therefore, the composites have a high dielectric constants and losses.

STUDY OF THERMAL AND DIELECTRIC BEHAVIOR OF LOW-DENSITY POLYETHYLENE COMPOSITES REINFORCED WITH ZINC OXIDE WHISKER

Different scanning calorimetry and dynamic mechanical analysis are used to study the thermal behavior of composites by melt-mixing low-density polyethylene (LDPE) matrix and zinc oxide whisker (ZnOw) fillers. Micrographs of the composites illustrate that needle or wedge shaped ZnOw are distributed uniformly in the LDPE matrix. Dielectric properties of the composites are measured in a frequency range of 1-10 MHZ. The results show that the addition of ZnOw does not affect the melting behavior of LDPE, but has an important effect on the heat of fusion, dynamic mechanical behavior, and dielectric behavior of the composites.