Wide angle X-ray diffraction studies of polytetrafluoroethylene and ethylen-tetrafluoroethylen-bipolymers in the range 9.5 K–270 K

Abstract

PTFE shows in the whole temperature range investigated a triclinic crystal structure with cell parametersa=0.952 nm,b=0.559 nm,c=1.706 nm,α=87.9°,β = 90.0° andγ=91.8°. The temperature dependence ofa andb-axis is linear, thec-axis shows a change in thermal expansion at 150 K. The inherent strain is small. The crystallite sizes are measured, paracrystalline distortions are absent.

The bipolymers show only an ordered arrangement in lateral direction under maintenance of the helical structure. The lateral arrangement is very distorted and the range of order is aboutD _L ∼ 10 nm.