REAL-TIME X-RAY-DIFFRACTION STUDY THROUGH THE CURIE TRANSITION OF THE 60/40 VINYLIDENE FLUORIDE TRIFLUOROETHYLENE COPOLYMER AS CRYSTALLIZED FROM THE MELT

Structural changes in the para-ferroelectric phase transition of the vinylidene fluoride-trifluoroethylene copolymer with 60/40 molar content have been investigated by means of real-time X-ray diffraction. A combined study of (i) long period from small-angle X-ray scattering, (ii) coherently diffracting domains derived from the integral width of the wide-angle reflections and (iii) lattice spacings offers the following picture. In the high-temperature region (65-140-degrees-C) the stacks of 250 angstrom thick paraelectric lamellae are found to consist of 250 angstrom wide coherently diffracting blocks. At the Curie transition (65-50-degrees-C) a breakdown of the large paraelectric crystals into thinner and smaller ferroelectric domains statistically mixed with the remaining paraelectric zones is observed. In the low-temperature region (T < 50-degrees-C), the ferroelectric phase is the predominant one (75%) though a fraction of non-polar crystals (25%) is also observed. It is further found that a part of the material in the non-polar phase can be associated with the trifluoroethylene structure, which is supported by the persistence of the corresponding reflection above the melting point of the copolymer.