The fine structure of polytetrafluoroethylene

Abstract

Electron micrographs of highly crystalline PTFE crystallized by slow cooling from temperatures not far above the melting point show well‐marked bands, often with striations perpendicular to the bands; optical evidence shows that the chain molecules are parallel to the striations. The structure is in marked contrast to the spherulitic structure of most polymers; it appears that in PTFE the molecules are straight and parallel for much greater distances than in other polymers, and it is suggested that the width of the bands is a measure of molecular length. The unusual structure is attributed to the unusual stiffness of the fluorocarbon chain; the molecules in the liquid are straighter and less tangled than in other polymer melts. Heating to 500°C., followed by slow cooling, gives a modified structure approaching the spherulitic type found in other polymers; it is suggested that this is due to increased molecular tangling in the melt at higher temperatures. One type of polymer shows bands of remarkably uniform thickness, suggesting unexpected uniformity of molecular length. PTFE wax made by thermal or radiation degradation of the high polymer shows well‐defined spiral growth steps due to dislocations; the step heights suggest an unexpected uniformity of molecular length.

Inclusion of perfluoromethyl groups in the crystals of copolymers of tetrafluoroethylene and hexafluoropropylene

“…These are smaller than typical homopolymer values which can be greater than 2.22 g/cm 3 • However, it would be incorrect to assume that lamella thickness is largely independent of copolymer concentration and then to attribute lowering of the density directly to reduced density [8] around the comonomer units without first considering the known tendency for lamella thickness to decrease with increasing comonomer content [I, 6, 7] . Since mispacking of the folds of adjacent lamellas lowers the gross density [20,21), copolymers should be less dense than the homopolymer simply because lamellas of the latter are often an order of magnitude thicker than the 350 to 500 A lamellas of the copolymers in figure 2 [22]. However, greater supercooling of the polytetrafluoroethylene melt produces samples with thinner lamellas.…”

In-situ Measurement of Crystalline Lattice Strains in Polytetrafluoroethylene

“…The first-order transition at 19°C between phases II and IV represents an untwisting in the helical conformation from 13 atoms/180 degree turn [12,13] to 15 atoms/turn [12,14,15] [ Fig. 1(a)] and an associated increase in the hexagonal lattice spacing [ Fig.…”

“Crystalline” Plastic Optical Fiber with Excellent Heat-Resistant Property

“…The proposed lattice constant of PTFE 23 corresponded to a = b = 11.08 Å, c = 16.8 Å, = 90°, = 90°, and = 119.3° (Fig. 8(b), quasi-hexagonal system) and improved upon the reports by Bunn, et al, Starkweather Jr., et al, Clark, et al, 18,[31][32][33] and other investigation groups ( Fig. 10(a), a = b = 5.54 Å, c = 16.8 Å, = 90°, = 90°, and = 119.3° (quasi-hexagonal system)).…”

“…The peak at around 2θ = 18.0° in the WAXD profiles of tetrafluoroethylene and its copolymers was assigned to the (100) reflection in the quasi-hexagonal system according to the literature documented about 50 years ago. 18,[31][32][33] Moreover, we could not find any reports related to the inner peak around 2θ = 9°. However, in the present WAXD profiles, small peaks at around 2θ = 9° were confirmed and reproduced well by the high-power measurement using an X-ray diffractometer with an imaging plate as the detector.…”