Lamellar and Crystal Structural Study on Ferroelectric Phase Transition of Vinylidene fluoride-Trifluoroethylene Copolymers by Synchrotron DSC/WAXD/SAXS Simultaneous Measurement

Japan Synchrotron Radiation Research Institute (JASRI)/Spring-8, Japan* Graduate School of Engineering Toyota Technological Institute, Japan** The RIKEN Harima Institute/Spring-8, Japan***
○H. Masunaga* S. Sasaki* M. Hanesaka** K. Tashiro** M. Takata*, ***

Vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymers show the ferroelectric phase transition at a Curie transition temperature. For the sample with VDF contents higher than 80 mol %, the transition occurs between the polar crystalline forms I, II and the nonpolar high-temperature phase. It has been found that the structural change in crystal lattice affects not only the inside of the crystalline lamella but also the morphological change of stacked lamellae drastically. However, the morphological change and its relation with the crystal structural change have not yet been clarified at all. In this work, we will report the experimental data concerning the simultaneous measurements of DSC/WAXD/SAXS during the heating and cooling processes of VDF 82% copolymer samples.
Simultaneous measurements of DSC, WAXD and SAXS were carried out at BL40B2 of SPring-8. WAXD and SAXS patterns from the sample were detected for 30 sec at 5 min-intervals in the heating and cooling processes at a rate of 1℃/min. In the heating process for the melt-quenched sample, the relative intensity of the reflection from the form II decreases and that from the HT phase increases instead in the endothermic temperature region of the DSC thermogram. On the other hand, the mean lamellar thickness and the long period of stacked lamellae, which were estimated from the one-dimensional electron density correlation function of SAXS profiles from the sample, increased largely and slightly due to thermal expansion, respectively. DSC/WAXD/SAXS data suggested that the phase transition form II to the HT phase enhanced lamellar thickening without large change in lamellar stacking distance.