Local variation of the dielectric properties of poly(vinylidene fluoride) during the alpha- to beta-phase transformation

Abstract

The phase transformation from the non-polar alpha-phase to the polar electroactive beta-phase of polyvinylidene fluoride (PVDF) has been investigated using the fluorescence from Nile red. Films of alpha-PVDF doped with Nile red were stretched at controlled rates at a temperature of 80 degrees C to produce the alpha- to beta-phase transition. The thermo/mechanical dependent changes in the crystalline structure are related to the physical rotation of the polar (CH2-CF2) group, which can he monitored by steady state fluorescence techniques. The degree of phase transformation is related to variation in the fluorescence, which ill turn is linked to local dielectric constant of the polymer. The variation of the refractive index is more associated to the alignment of the polymeric chains than to the phase transformation. Thus, fluorescence is a suitable technique to monitor phase transitions coupled to a variation in the polarity of the dielectric medium. (C) 2008 Elsevier B.V. All rights reserved.