The Study Of Dielectric Properties Of Polymer Matrix Nanocomposite Films At Low Frequency

BaTiO₃（BT） with various diameters were synthesized by alkoxideroute and then loaded into different polymers poly （vinylidene fluoride）（PVDF） and polyimide （PI）) at50vol.%to fabricate PVDF/BT andPI/BT nanocomposite films. The effects of nanoparticles and polymermatrixes on dielectric properties were studied by two differentmeasurement procedures in a wide range of frequency from10-2Hz to106Hz. A significant low-frequency dielectric permittivity increase wasdiscussed. Interfacial polarization, crystal phase effect and thermalagitation are considered to analyze the significant increase at lowfrequency. A significant discrepancy between PVDF/BT and PI/BT indielectric behaviors was found and discussed. Herein, nano particlesinfluenced more on dielectric behavior in PVDF/BT than that of PI/BT. Itresuled from the strong polyarity of PVDF matrix. Meanwhile, dielectricbehavior in PVDF/BT was dependent on temperature due to the thermalplastic structure of PVDF, while that of PI/BT was not for the high glass transition temperature of PI and thermalset sturcuter. In addition,theoretical models were used to predict dielectric permittivities ofnanocomposite films. The observed dielectric permittivities are in goodagreement with calculated values when the interactions ofnanoparticle-polymer and the shapes of nanoparticles were considered.Therefore, the roles of nanoparticles （size and crystal phases） andproperties of polymers （chemistry and chain structure） are considered toexplain the difference in dielectric behaviors. Meanwhile, the dielectricproperties were also affected a lot by the frabrication methods and thedispersity of the nanoparticles in the matrix.