Pressure Dependence of Transitions and Relaxations in Polytetrafluoroethylene

The ultrasonic absorption and linear thermal expansion behavior of polytetrafluoroethylene in a hydrostatic high pressure vessel (piston and compound cylinder type) capable of achieving 16,000 kg/cm 2 are measured in the temperature from -30°C to 200°C and in the pressure from 1 atm. to 5,000 kg/cm 2 . Ultrasonic (5 Mc/s carrier frequency) attenuation maxima at atmospheric pressure are found at about -12°C, 30°C, 50°C, 130°C and 140°C, and pressure dependence of these maxima is found as about 10, 9, 28, 13, and 25 degrees per 1,000 kg/cm 2 , respectively. From these facts and the dispersion map, the third, fourth and fifth peaks indicate important informations of existence of segmental motion in amorphous regions (primary dispersion), crystalline dispersion and grain-boundary dispersion, respectively. By a thermodynamical consideration and the thermal expansion behavior, the second peak is defined as the one due to the 30°C transition.