Nanoscale View of Alignment and Domain Growth in a Hexagonal Columnar Liquid Crystal

Area of Science:

• Materials Science
• Condensed Matter Physics
• Organic Electronics

Background:

• Highly ordered liquid crystalline (LC) phases are crucial for advanced applications in organic electronics.
• Understanding the nanoscale molecular alignment and domain structure evolution in LC thin films is essential for optimizing device performance.

Purpose of the Study:

• To investigate the in situ molecular alignment and domain reorganization mechanisms in columnar liquid crystalline thin films during heating.
• To explore the role of intermediate crystallization in manipulating the nanoscale structure and orientational order of LC thin films.

Main Methods:

• Utilized four-dimensional scanning transmission electron microscopy (4D STEM) for high-resolution, in situ analysis of LC thin film structure during thermal treatment.
• Observed the transition from a disordered vapor-deposited LC glass to ordered columnar phases and intermediate crystalline states.

Main Results:

• Identified rapid ordering into a hexagonal columnar phase with small (<10 nm), well-aligned domains upon reaching the glass transition temperature.
• Documented domain coarsening via bulk diffusion, followed by crystallization, and a subsequent transformation back to an LC phase at higher temperatures.
• Observed straight molecular columns in the high-temperature LC phase, attributed to structural inheritance from the intermediate crystalline phase.

Conclusions:

• Nanoscale 4D STEM provides direct insights into the dynamic mechanisms of domain reorganization in LC thin films.
• Intermediate crystallization presents a viable strategy for controlling nano- to mesoscale orientational order and texture in liquid crystalline materials.
• The findings offer a pathway to engineer LC thin films with tailored structures for enhanced organic electronic applications.