Influence of filler size and concentration on the low and high temperature dielectric response of poly(vinylidene fluoride) /Pb(Zr0.53Ti0.47)O3 composites

Poly(vinylidene fluoride)/Pb(Zr0.53Ti0.47)O3([PVDF]1−x/[PZT]x ) composites of volume fractions x and (0–3) type connectivity were prepared in the form of thin films. The films were prepared by solvent casting with PZT powder of 0.84, 1.86, and 2.35 μm average size with filler contents up to 40% volume. The crystalline phase of the polymer matrix was the nonpolar α-phase and the polar β-phase. Dielectric measurements were performed in order to evaluate the influence of the filler size and content as well as the effect of the polymer matrix in the overall response of the material. No nucleation effect of any of the phases was observed for the used fillers. The spherulitic structure of the pure α-PVDF and the characteristic porosity of the β-phase material are destroyed for high PZT volume fractions. The inclusion of ceramic particles in the PVDF polymer matrix increases the complex dielectric constant of the composites independently of the PVDF polymer matrix. The dielectric properties of the composites are mainly affected by the amount of the ceramic particles. With respect to the relaxation processes of the polymer, the activation energy of the a-relaxation increases and the glass transition temperature decreases with increasing particle size and content. The high-temperature conductivity decreases with increasing filler content and there is an important contribution of the Maxwell-Wagner-Sillars effect to the overall dielectric response.This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade - COM-PETE" and by national funds by FCT-Fundacao para a Ciencia e a Tecnologia, project references PTDC/CTM/69316/2006, PTDC/CTM-NAN/112574/2009, and NANO/NMed-SD/0156/2007. V. S., S. Firmino Mendes and C. M. Costa thank the FCT for the SFRH/BPD/63148/2009, SFRH/BD/22506/2005 and SFRH/BD/68499/2010 grants, respectively. JLGR acknowledge the support of the Spanish Ministry of Education through project No. MAT2007-66759-C03-01 (including the FEDER financial support), and founding in the Centro de Investigacion Principe Felipe in the field of Regenerative Medicine through the collaboration agreement from the Conselleria de Sanidad (Generalitat Valenciana), and the Instituto de Salud Carlos III (Ministry of Science and Innovation). The authors thank the support from the COST Action MP1003, 2010, 'European Scientific Network for Artificial Muscles' (ESNAM)