Lamellar Structure in Melted-Slowly Cooled Vinylidene Fluoride/Trifluoroethylene (86/14) mol% Copolymer

Lamellar structure, and its thermally induced changes in melted-slowly cooled vinylidene fluoride/trifluoroethylene (86/14) mol% copolymer were studied by scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS). SAXS intensity data observed at room temperature showed peaks at arounds≃7.5 ×10-3Å-1ands≃1.35 ×10-3Å-1, the latter of which is caused by thick lamellar stacks such as those observed by SEM (sis the magnitude of the scattering vector). During the heating process, the higher-angle peak disappeared at 147–155°C, while the lower-angle peak disappeared at around 170°C (the melting point of the sample). These SAXS data were analyzed by fitting to lamellar stack models. For the data in the range 25–147°C, a model in which thin and thick lamellar stacks coexist was used. For the data in the range 155–165°C, a model in which only thick lamellar stacks exist was used. The calculated intensities were in good agreement with the observed intensities, which demonstrates that in the range 25–147°C the copolymer is composed of stacks of lamellae about 85 Å thick and stacks of lamellae about 570 Å thick, and that in the range 155–165°C it is composed of only the thick lamellar stacks. The mean crystallinity of the thin lamellar stacks was found to decrease markedly with increasing temperature, which indicates that thin lamellar stacks disappear in the range 147–155°C due to the melting of the crystals within them.