In Situ 4D-STEM Imaging of the Orientation of Lamellar Clusters in Polymer Crystallization.

In semi-crystalline polymeric materials, the initial stages of nucleation and the growth path of crystalline domains can determine the final performance. Here, we used four-dimensional scanning transmission electron microscopy (4D-STEM) imaging to analyze the changes in lamellar orientation in high-density polyethylene (HDPE) during heating and cooling. This method allowed us to quantitatively detect the formation of lamellae clusters with different in-plane orientations, which are not visible with traditional methods. Our analysis provided detailed insights into the orientation and size changes of crystalline domains. Additionally, this technique enabled direct observation of lattice structures in hierarchical lamellae and the growth of crystals, confirming the local variability in lamellar orientation. This innovative approach significantly improves our understanding of polymer crystallization, linking changes in morphology and lattice structures at different length scales.