Elucidating the Hierarchical Architecture of Polymer Spherulites via 4D Scanning Transmission Electron Microscopy

TL;DR

This paper uses advanced electron microscopy to study the complex structures of polymer spherulites, revealing new details about their formation and organization.

Contribution

The study introduces low-dose 4D-STEM as a novel method for visualizing polymer spherulite architecture at multiple scales.

Findings

4D-STEM reveals preferential orientation and growth direction of lamellar crystals in polymer spherulites.

A non-radial twisting axis and spiral texture in PE banded spherulites are observed.

Cryogenic 4D-STEM enables visualization of chain tilt and lamella configurations at the nanoscale.

Abstract

Hierarchical spherulite structures are ubiquitous in semicrystalline polymers and impact their properties. Elucidating these delicate and complex structures, which span from molecular‐level chain folding to mesoscale spherulites, however, presents a formidable challenge. Here, we showcase low‐dose four‐dimensional (4D) scanning transmission electron microscopy (STEM) as a powerful technique for investigating the multiscale hierarchical structures of polymer spherulites. Applying it to poly(ε‐caprolactone) and polyethylene (PE) spherulite films, we reveal the preferential orientation and growth direction of lamellar crystals, as well as the twisted lamella structure in PE banded spherulites. Notably, our observations reveal a non‐radial twisting axis forming a spiral texture in PE films. With the enhanced spatial resolution of cryogenic 4D‐STEM, we directly visualize individual lamellar crystals at the nanoscale, enabling the identification of chain tilt within a single lamella and the elucidation of lamella configurations at spherulite boundaries. These insights advance our understanding of polymer spherulite crystallization mechanisms and underscore low‐dose 4D‐STEM as a powerful tool for exploring the intriguing structures of soft materials.

By using low‐dose four‐dimensional (4D) scanning transmission electron microscopy (STEM) on the multiscale hierarchical structures of poly(ε‐caprolactone) and polyethylene (PE) spherulite films, the preferential orientation and growth direction of lamellar crystals, chain tilt within single lamella, as well as the twisted lamella structure with spiral texture in PE banded spherulites are revealed.

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