An internal friction study of polytetrafluoroethylene

Author:
Publisher website
Google Scholar
Abstract
A torsion pendulum has been used to measure the internal friction of polytetrafluoroethylene. The crystallinity of the specimens varied form 48 to 92%, and the measurements were made over a wide temperature range. The site of each relaxation was assigned by observing the variation of relaxation strength and peak height with crystallinity. In this way amorphous relaxations were found to occur at 176.5°K. (0.60 cycle/sec.) and 399°K. (0.62 cycle/sec.). The crystallite relaxations occur at 291°K. (0.28 cycle/sec.) and the crystallite melting point, 600°K. It is concluded that the amorphous regions of polytetrafluoroethylene exist in three phases between 4.2°K. and the crystallite melting point. The supercooled liquid which exists below 600°K. is transformed into an amorphous solid at a temperature in the region of 400°K. This solid undergoes another transformation at approximately 176°K. to form a third phase which is stable down to 4.2°K. The crystallite realaxation centered at 291°K. consists of a series of disordering transitions including the well‐known first‐order transition. There is evidence that hindered rotation occurs within the crystallites at temperatures as low as 220°K.

This publication has 16 references indexed in Scilit: