Mesogen-co-polymerized transparent polyimide as a liquid-crystal alignment layer with enhanced anchoring energy

Area of Science:

• Materials Science
• Polymer Chemistry
• Display Technology

Background:

• High azimuthal anchoring energy is crucial for advanced liquid-crystal displays (LCDs).
• Existing alignment films require enhancement for superior liquid-crystal (LC) molecule control.

Purpose of the Study:

• To design and synthesize a novel transparent polyimide (PI) with mesogenic side chains for improved LC alignment.
• To investigate the effect of mesogenic side groups on the anchoring energy of PI alignment films.

Main Methods:

• Synthesized a pyrimidyl diamine monomer with a cyanobiphenyl mesogenic unit.
• Co-polymerized the monomer with 4,4'-diaminodiphenyl ether and 4,4'-oxydiphthalic anhydride to create the PI.
• Evaluated PI properties including thermal stability, mechanical strength, optical transparency, and surface anchoring energy using a micro-electro-mechanical balance system.

Main Results:

• The novel PI demonstrated good thermal stability, mechanical properties, and high optical transparency (86% transmittance from 450-700 nm).
• The PI with mesogenic side chains exhibited a 2.2-fold increase in surface anchoring energy compared to unmodified PI.
• Appendage of mesogenic groups strengthened intermolecular interactions between the PI surface and LC molecules.

Conclusions:

• The developed polyimide is a promising candidate for liquid-crystal alignment films due to its transparency and enhanced anchoring energy.
• The strategy of using mesogens to align liquid crystals offers a new approach for designing advanced alignment materials.