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.
Temporal changes of the weight, volume, temperature and elastic properties during the dehydration process of a polyacrylamide (PAAm) gel were studied. Both the weight and the volume monotonically decreased in the early stage of the process and then tended to saturate in the late stage. At the crossover point between these two dependencies, the temperature of the gel and its elastic stiffness showed anomalies, which indicated similar aspects to the glass transition often observed in non-crystalline polymers. The water content in gels is an important factor affecting the transition.
Simultaneous measurements of weight, volume and mechanical properties have been performed during the gel-to-glasslike transition of heat-treated egg-white gel. Change in the elastic stiffness occurred in three steps: in the initial stage, it remained almost constant, then increased exponentially, and lastly, saturation was attained. The saturation point almost coincided with the characteristic time at which the rates of decrease of the weight and volume changed. In addition, from the time dependence of the differentiated values, the close correlation between the elastic stiffness and weight was revealed. It was also found that the loss of free water induces an increase of about a thousardfold in elastic stiffness of gels during transition.
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