Dielectric relaxations in copolymers of vinylidene fluoride

Abstract

Ferroelectric copolymers of vinylidene fluoride with trifluoroethylene and tetrafluoroethylene have been investigated by means of broad band dielectric spectroscopy (10 mHz-1 GHz) at temperatures covering the ferroelectric, paraelectric and molten phases as well as the glassy and rubbery states. The low-temperature relaxation spectra near T, (--40°C) consist of two processes; a WLF-type segmental mode and an Arrhenius type local mode. These processes are unified near room temperature to be transferred continuously to the high-temperature process. After showing a peak at the Curie point T, (70-140"C), the relaxation strength decreases gradually in the paraelectric phase until the melting point T, (-150°C) is reached, where it decreases rapidly. It is found that the relaxation time in the molten phase lies on the Arrhenius line extended from the low-temperature local mode process. This implies that related molecular motions arise from a common elementary process. Departure from this Arrhenius line in the paraelectric phase is discussed by the use of a cooperative multi-site model.

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

“…8(a)] are like those for a classical ferroelectric polymer-copolymer of VDF and trifluorethylene TrFE of 65/35 ratio. 31 Differences are that for the latter the peak on e 0 (T) curve in the Curie point is more intensive. Use of classical representations of such transitions by temperature dependencies of reciprocal dielectric permittivity w ¼ 1/e 0 can serve as additional argument to ascribe the considered process to a ferroelectric-paraelectric phase transition.…”

Temperature and frequency dependence of the dielectric and piezoelectric response of P(VDF–TrFE)/CoFe2O4 magnetoelectric composites

“…The homogeneity of the fillers can be reflected in dielectric spectra as well. PVDF-TrFE has the well-known relaxation which is related to the micro Brownian cooperative motions of the main chain backbone and is a dielectric manifestation of the glass transition temperature of PVDF and PVDF-TrFE copolymers [19][20][21]. In addition, earlier works showed that the crystallinity content of PVDF-based composites varies with the filler type and content [22].…”

“…These broad dielectric loss peaks below 300 K (Fig. 2) are known as the β-relaxation process [19][20][21] and usually referred to the glass transition of P(VDF-TrFE) copolymer. The behaviour of this anomaly is characteristic of the ones observed in semicrystalline polymers [21].…”

Upper bounds on the electrocaloric effect in polar solids

“…At saturation, the polarization P͑E , T͒ reaches the value P sat = Np / V = p / v, where p is the average dipole moment of a dipolar entity. Using p = vP sat and the relation ⌰ = p 2 / ͑3kv 0 ͒, which has been derived within a molecular field-type approach for a system of interacting dipoles in three dimensions, 6 we can eliminate p and write v =3 0 k⌰ / ͑P sat 2 ͒. Substituting this v into Eq.…”