Microwave Dielectric Characteristics Of Polyvinylidene Fluoride-Polyaniline And Polypropylene-Ag Percolative Dielectric Composites

Polyvinylidene fluoride (PVDF) and conductive polyaniline (PANI) were used as the matrix and conductive filler, respectively, and PVDF-PANI percolative dielectric composites were prepared by hot pressing. The dielectric properties were characterized at1-107Hz and microwave frequencies. The room-temperature dielectric constant and dielectric loss reached the peak value with PANI volume fraction of0.13at1-107Hz. The composites were conductive when the PANI volume fraction was higher than0.14, indicating the typical percolative dielectric properties in the frequency range of1-107Hz. Significant dielectric relaxation was observed for all composites, which could be well fitted by Vogel-Fulcher relationship, indicating that dielectric relaxation derived from β phase transition of PVDF. The composites also exhibited similar percolative dielectric behavior in the frequency range of3.62-7.30GHz when PANI volume fraction was less than0.14. This indicated that the interfacial polarization dominated the dielectric properties up to microwave frequencies, although it was usually regarded to contribute to the dielectric properties at frequencies lower than105Hz.In order to study further on the microwave dielectric characteristics of percolative dielectric composites, Polypropylene(PP)-Ag percolative dielectric composites were also prepared by hot pressing and characterized, since the weak dielectric relaxation of PP and high conductivity of Ag. The room-temperature dielectric constant and dielectric loss reached the peak value with Ag volume fraction of0.17. The composites were conductive when the Ag volume fraction was higher than0.17, exhibiting typical percolative dielectric properties in the frequency range of1-107Hz. Weak dielectric relaxation was observed in all composites, which was similar with PP. The composites also exhibited similar percolative dielectric behavior in the frequency range of3.62-11.43GHz, indicating that the interfacial polarization dominated the dielectric properties up to microwave frequencies. With further increasing Ag volume fraction, the dielectric constant and dielectric loss at microwave frequencies were unmeasurable due to the interconnected silver conductive network, which was similiar with1-106Hz and may derive from the high conductivity of Ag.