Dielectric relaxation in vinylidene fluoride-hexafluoropropylene copolymers

The molecular mobility in copolymers of vinylidene fluoricle-hexafluoropropylene VDF/HFP of 93/7 and 86/14 ratios has been investigated by means of broadband dielectric relaxation spectroscopy (10(-1)10(7) Hz), differential scanning calorimetry DSC (-100 to 150 degrees C), and of wide angle X-ray diffraction WAXS. Four relaxation processes and one ferroelectric-paraelectric phase transition have been detected. The process of the local mobility beta- (at temperatures below glass transition point) is not affected by chemical composition of the copolymer and the formed structure. Parameters of segmental mobility in the region of glass transition (alpha(a)-relaxation) depend on the ratio of comenomer with lower kinetic flexibility. alpha(a)-relaxation is clearly observed only in VDF/HFP 93/7 copolymer, which is characterized by a higher crystallinity and a higher perfection of crystals of alpha- (alpha(p)-) phase. Diffuse order-disorder relaxer type ferroelectric transition connected with the destruction of the domains in low-perfect ferroelectric phase in the amorphous regions has been detected for both copolymers. An intensive relaxation process (a-process) was observed for both copolymers in high-temperature region. DSC data shows that it falls on the broad temperature region of alpha-phase crystals melting. It is considered to be connected with the space charge relaxation. (c) 2007 Wiley Periodicals, Inc.