Transmission Electron Microscopy Methodology to Analyze Polymer Structure with Submolecular Resolution

The crystallinity of polymeric materials defines their properties, in particular, the mechanical ones. High-resolution transmission electron microscopy (TEM) imaging of polymers would be critical to address intricate polymer crystallinity, yet it is challenging due to polymer sensitivity to the electron beam. We performed high-resolution TEM imaging of polycaprolactone (PCL) thin films employing low-dose focal series reconstruction (LDFSR). LDFSR enabled submolecular resolution imaging of polymer crystals. The direct imaging study was augmented by scanning nanobeam electron diffraction (NBED) using the 4D STEM technique to map micro- and nanoscale crystalline domains. Employing LDFSR combined with 4D STEM, we directly observed interacting polymer chains in the crystal lattice, elucidating the crystal structure with a high degree of precision including lattice deformations. We also imaged PCL lamella using conventional TEM. Our methodology enables long-sought insights into the polymer structure, introducing a new tool for high resolution studies of polymer crystallinity that fills a critical gap in the structural science of polymer materials.