| Popis: |
The intermolecular and intramolecular disorders, and the crystalline phase transition in poly(tetrafluoroethylene) are examined by X-ray diffraction between 20° and 250°C. A presence of the crystalline phase transition around T t = 150°C is confirmed by the rapid decrease in the intensity of the Bragg reflection 1015. This phase transition is ascribed to the abrupt increase of the intermolecular translational disorder along the chain. From the quantitative analysis of the profile of the 0015 reflection, it is found that the increase in the translational disorder described above is accompanied by the excitation of the intramolecular disorder in conformation. The intramolecular disorder in conformation below T t is found to be due mainly to the thermal excitation of trans conformation in the usual 15-7 helix. Further increase in disorder in conformation is found above T t , which is due to the excitation of gauche conformation. The fraction of trans conformation increases up to 40% with the increase of temperature, in good agreement with the theoretical calculation. The fraction of gauche conformation above T t is also estimated to give, for example, 7.5 × 10 −3 at T = 214°C. |
