Radiation damage of polyethylene single crystals in electron microscopy between 1 and 2.5 MV. II. The influence of temperature

Abstract

2014 Influence de la température sur la dégradation des monocristaux de polyéthylène en microscopie électronique à haute tension : des mesures de dose critique effectuées sur des monocristaux de polyéthylène à 2 MV montrent que cette dose augmente d'un facteur 4 environ de 300 K à 20 K. En dessous de 100 K, la phase cristalline hexagonale intermédiaire n'est pas observée. De ces mesures, on a pu calculer le facteur G de création de réticulations et on a montré qu'il était proportionnel à la température. Enfin nous proposons un nouveau modèle pour expliquer l'influence de la température sur la dose critique, dans le cadre des systèmes de transformation, dont l'avantage est d'être calqué sur les mécanismes réels décrits par les chimistes. Abstract. 2014 The critical dose measured for polyethylene single crystals at 2 MV is increased by a factor of 4 between 300 K and 20 K. Below 100 K the intermediate hexagonal crystalline phase was not observed. From these measures, the number of cross-links created, factor G, was calculated, and it appeared to be proportional to temperature. Finally, we propose a new model tempting to explain the influence of temperature on the critical dose. It follows the formalism of transformation systems and has the advantage to match to the real mechanisms as described by chemists.

Glassy cholesteric structure: thickness variation induced by electron radiation in transmission electron microscopy investigated by atomic force microscopy

“…However, the observations in TEM of liquid crystals, liquid crystal polymers, or other polymers and, more generally, all organic substances are limited by the low contrast exhibited by these materials and by the radiation damage undergone by the specimens inside the microscope. It has long been established that a loss of mass occurs [5,6], and that crystalline specimens are damaged and changed into an amorphous material [5,[7][8][9][10]. The remaining contrast is due only to variations of mass density or of thickness or both.…”