Fine Structure of the III-I Transition and Molecular Motion in Polytetrafluoroethylene

The fine structure in the III-I transition region and the molecular motion of polytetrafluoroethylene under high pressure have been studied by X-ray diffraction and nuclear magnetic resonance. In the transition region from the high pressure phase III to phase I, two kinds of crystals were observed to coexist over a considerably wide temperature range. This fact suggests that the abnormal attenuation of ultrasonic waves reported in this transition region is due to a density fluctuation of these crystals. Also, a detailed study on the molecular chain conformation and the molecular motion in phase I revealed that there exists in the higher temperature region of phase I a new region, where the molecules have apparently a planar zigzag conformation as a result of right-handed and left-handed helical thermal motions in molecular chains.