Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

Abstract

The molecular mobility in copolymers of vinylidene fluoride-hexafluoropropylene VDF/HFP of 93/7 and 86/14 ratios has been investigated by means of broadband dielectric relaxation spectroscopy (10 À1 -10 7 Hz), differential scanning calorimetry DSC (À100 to 1508C), 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 b-(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 (a a -relaxation) depend on the ratio of comonomer with lower kinetic flexibility. a c -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 a-(a p -) phase. Diffuse order-disorder relaxor 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 aphase crystals melting. It is considered to be connected with the space charge relaxation.

Dielectric relaxations in PVDF/BaTiO3 nanocomposites

“…The presence of α a relaxation peak in PVDF/BaTiO 3 nanocomposites explains the non-polar i.e. α phase of PVDF in nanocomposites [20]. Several interpretations of these transitions are reported [21][22][23].…”

Multifunctional nanocomposites of poly(vinylidene fluoride) reinforced by carbon nanotubes and magnetite nanoparticles

“…The frequency limit of the instrument constrained the full view of this relaxation. However, earlier works have confirmed the peak around 1 MHz is related to the micro-Brownian cooperative motions of the main chain backbone and is essentially the dielectric manifestation of the glass transition temperature of the PVDF [46][47][48]. The second relaxation peak observed at lower than 10 Hz is the !…”

“…The second relaxation peak observed at lower than 10 Hz is the ! c relaxation and is attributed to molecular motions (rotation and twisting with a small lengthwise translation of the crystalline chain) of the PVDF crystalline region [47]. [48].…”

Clay nanocomposites based on poly(vinylidene fluoride-co-hexafluoropropylene): Structure and properties

“…Four processes are typically seen for such copolymers [48][49][50]. A β relaxation below -40 o C due to local dynamics in the polymer chains, a relaxation around -40 o C due to the glass transition of the amorphous phase, a relaxation of the crystalline phase above 0 o C and an order-disorder transition of the ordered ferroelectric phase at even higher temperatures.…”