Polyvinylidene difluoride-based composite: glassy dynamics and pretransitional behaviour

This paper presents results of broadband dielectric spectroscopy studies in the composite system for which particularly strong interactions between polyvinylidene difluoride (PVDF: ferroelectric polymer, T-C = 453-473 K) matrix and barium strontium titanate (BST) ferroelectric micro-particles can be expected. For PVDF the super-Arrhenius (SA) dynamics, associated with segmental motions freezing at the glass temperature T-g = 235 K, is evidenced. The addition of BST particles qualitatively changes dynamics, converting the SA-type behaviour in PVDF to the clear Arrhenius one in BST/PVDF composite. The latter crossovers to the relaxor-type SA dynamics on cooling, exactly at the glass temperature of PVDF. The preliminary model explaining such unique behaviour is proposed. For the consistent portraying of the SA evolution of primary relaxation times in PVDF and BST/PVDF, the activation energy index analysis was carried out and the new equation, entropy and symmetry controlled, is introduced. Studies are accomplished by the analysis of the ferroelectric-paraelectric transition in PVDF and for the composite system. They led to the discovery of the strong pretransitional anomaly of d epsilon/dT, extending even to the vicinity of the room temperature, The semi-discontinuous nature of melting in PVDF and its composites, with the discontinuity metric oT approximate to 20 K is suggested.