Analysis of the structure and morphology of crystalline polymers by electron microscopy imaging and diffraction: a personal journey.

Crystalline polymers form complex spherulitic morphologies upon crystallization from the melt. The spherulites are made of thin lamellae, frequently twisted, in which the long chains span the lamellar thickness and are folded back and forth at the lamellar surface. Investigation of the crystalline and lamellar structures becomes, however, possible by using single crystals, the size and thickness of which are well adapted for transmission electron microscopy. Imaging in bright and dark field modes, electron diffraction and specific decoration techniques have made it possible to reach a detailed understanding of lamellar and surface structures as well as the crystallization processes. These insights are transferable to the more complex bulk architectures and thus help analyze some of their most striking features. Electron microscopy turns out to be a major tool and in many cases the only possible tool to reach such molecular and even sub-molecular understanding. Some of these insights are illustrated, based mostly on work performed in our laboratory. They involve some original experimental techniques that should be useful in materials science.