Three-Dimensional Visualization and Characterization of Polymeric Self-Assemblies by Transmission Electron...

Area of Science:

• Polymer Science and Engineering
• Materials Science
• Nanotechnology

Background:

• Block copolymers (BCPs) self-assemble into complex nanoscale periodic structures (microphase-separated structures).
• Understanding these structures is crucial for advanced nanomaterials, but their increasing complexity challenges characterization.
• Three-dimensional imaging techniques are essential for studying these intricate morphologies, especially during dynamic processes.

Purpose of the Study:

• To demonstrate the utility of 3D-TEM for investigating BCP nanostructures, particularly during dynamical processes and under confinement.
• To analyze order-order transitions (OOTs) in BCPs and their phase transition paths.
• To explore novel methods for in situ 3D electron tomography of polymer materials.

Main Methods:

• Utilized three-dimensional transmission electron microscopy (3D-TEM) to visualize BCP nanostructures.
• Examined dynamical processes like OOTs by capturing snapshots of specimens during transitions.
• Developed new contrast enhancement techniques (chemical differences, no staining) and a 3D reconstruction algorithm for improved in situ imaging.

Main Results:

• 3D-TEM successfully characterized complex BCP morphologies formed during OOTs and under confinement.
• Identified two distinct epitaxial phase transition paths during an OOT between gyroid and cylindrical structures, dependent on transition direction.
• Demonstrated a new staining-free contrast enhancement and a more efficient reconstruction algorithm for 3D electron tomography.

Conclusions:

• 3D-TEM is an indispensable tool for studying complex BCP self-assembly, including dynamic events and confined structures.
• The developed in situ electron tomography methods overcome key limitations, paving the way for real-time 3D structural observations of polymers.
• These advancements will facilitate the design and fabrication of high-performance nanomaterials with tailored properties.