Effect of the ceramic grain size and concentration on the dynamical mechanical and dielectric behavior of poly(vinilidene fluoride)/Pb(Zr0.53Ti0.47)O3 composites

In this work, poly(vinilidene fluoride)/Pb(Zr0.53Ti0.47)O-3([PVDF](1-x) /[PZT] (x) ) composites of volumetric fractions x and (0-3) type connectivity were prepared in the form of thin films. PZT powder of crystallite size of 0.84, 1.68, and 2.35 mu m in different amounts of PZT (10, 20, 30, and 40%) was mixed with the polymeric matrix. The crystalline phase of the polymeric matrix was the nonpolar alpha-phase and the polar beta-phase. Dielectric and dynamic mechanical (DMA) measurements were performed to these composites in order to evaluate the influence of particle size and the amount of PZT filler with respect to the PVDF matrix. The inclusion of ceramic particles in the PVDF polymer matrix increases the complex dielectric constant and dynamical mechanical response of the composites. A similar behavior is observed for the alpha- or beta-phase of the polymeric matrix indicating that the PVDF polymer matrix is not particularly relevant for the composite behavior. On the other hand, ceramic size and especially content play the major role in the increase of the dielectric response and the room temperature storage modulus. In particular, the storage modulus increases with increasing PZT concentration, but this increase is more pronounced, in terms of maximum value, for the sample with 2.35 mu m particle size; DMA reveals two main relaxations in the analyzed samples. A low-temperature process maximum at ca. -40A degrees C, usually labeled by beta or alpha (a) associated to the T (g) of the polymer and the alpha-relaxation at temperatures above 30A degrees C. The beta-relaxation is also observed in the dielectric measurements. The models used to asses the dielectric behavior of the samples with increasing PZT concentration indicate that the particle-matrix interaction plays a relevant role, as well as the particle asymmetry and relative orientation, being the Yamada model the most appropriate to describe the composite behavior.