Regular rotation of growth terraces in polymer single crystals

Abstract

Polymer single crystals can sometimes be observed to consist of spiral growth terraces centered on screw dislocations where consecutive terraces are rotated with respect to each other in the same direction by the same amount throughout the crystal leading to spectacular growth features. Over the years such crystals have been examined by a variety of techniques thanks to the contribution ofS. Mitushashi, D. C. Bassett, P. H. Harris andB. Lotz in our laboratory. These examinations involved optical and electron microscopy in the latter case involving transmission, replication, electron diffraction, dark field effects and sectioning. It was concluded that the effect is associated with the pyramidal nature of the crystals, in particular to layers of differing obliquities being wrapped around each other. This structure could be due to shear transformation following primary crystal growth—an effect apparent from earlier studies on monolayer crystals—when this is associated with multilayer crystal development. Accordingly the rotated terrace crystals would reflect a general phenomenon in polymer crystallization which under special circumstances can lead to the conspicuously regular features in question.