Molecular Structure in Crystal Aggregates of Linear Polyethylene

Abstract

Crystal aggregates of linear polyethylene hare been studied in the electron microscope. Twinning has been observed to occur across (530) planes, and possibly across (120) planes. Crystal morphologies have been observed which exhibit (530) and (5.40) faces. Electron interference effects have been observed which give rise to contrast lines and figures which frequently are parallel to crystallographic directions. These observations, and those of others, have been interpreted in terms of recently proposed ideas on molecular chain folding. It is suggested that chain folds may lie in a variety of fold planes or fold surfaces which are normal, or nearly normal, to the crystal lamellae. It is shown that a continuity of fold structure is necessary and possible across a wide variety of boundaries delineating regions of different fold structure. It is shown that these structural concepts are compatible with recently proposed ideas on the growth of lamellar polymer crystals and can suggest new details of the growth process.