Morphology evolution in polytetrafluoroethylene as a function of melt time and temperature. Part III. Effect of prior deformation

Abstract

In parts I and II the effect of melt time and temperature on dispersed dispersion particles of various molecular weights was described: substantial molecular motion on the substrate occurs with the development of both planar folded chain single crystals, and single molecule single crystals and banded structures with parallel double-striations oriented along the long axis of the crystal or band. The molecules in the single molecule single crystals and bands are parallel to the substrate, an individual double-striation appearing to consist of a ‘double edge’, folded chain, lamella more or less normal to the substrate. In this paper, the effect of deformation and subsequent heat treatment of the nascent particles is described. Similar to the known effect of deformation of compacted nascent PTFE dispersion particles, large scale shear of dispersed dispersion particles can lead to nano-fibrils of indefinite length for both standard size resins and nano-emulsions, of both high and low molecular weight. Sintering of the nano-fibrils in contact with the substrate leads to the development of shish–kebab structures with the nano-fibril as a core and epitaxially nucleated, ‘double edge’, folded chain single crystal kebabs oriented perpendicular to the fibril axis and the substrate. No change is seen in similar fibrils remaining suspended between the dispersion particles. The molecules forming the ‘kebabs’ have ‘wandered’ individually on the substrate (glass) before attaching to the growing kebabs.