On Annealing and Ferroelectric Behavior in Poly(Vinylidene Fluoride-Trifluoroethylene) Random Copolymers
Abstract
Random copolymers of Vinylidene-Fluoride (VF2) and Trifluoroethylene (VF3) having high vinylidene fluoride content are known to crystallize from the melt into the most polar all-trans phase-I crystal form. After poling, these P(VF2-VF3) copolymers have been shown to exhibit significant piezoelectric and pyroelectric response allowing for their use as sensors and actuators. It was also believed that crystallization of these polymers above or below their respective Curie temperatures, (Tc) resulted in the production of a ferroelectric phase. However, studies in our laboratory have shown that samples quenched from the melt to below Tc are not ferroelectric. In order to determine whether or not a ferroelectric phase can be recovered in these materials by subsequent annealing, we performed annealing studies on two of the copolymers: the 80:20 and 73:27 compositions of P(VF2-VF3). As a function of annealing temperature, the remanent polarization, Pr, was observed to increase slowly up to 40° C and then rapidly increase between 40° C and 50° C and then show little increase until just below the Curie temperature range is reached at 90° C, indicating that the copolymers do indeed gradually transform to a ferroelectric state. We also present a series of wide angle x-ray diffraction, (WAXD), results that show the presence of a mixture of phases I and II in the as-quenched material. A clear development of phase I content at the expense of a decrease in phase-II content is observed as the annealing temperature increases.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2002
- Bibcode:
- 2002APS..MARB33042C