Optically active polyaniline film based on cellulose nanocrystals

Area of Science:

• Materials Science
• Polymer Chemistry
• Nanotechnology

Background:

• Chiral nematic liquid crystals, such as cellulose nanocrystals (CNCs), possess inherent optical activity.
• Polyaniline (PANI) is a conducting polymer with potential applications, but its chirality is typically limited.
• Achieving controlled chirality in polymer films is crucial for advanced optical and electronic devices.

Purpose of the Study:

• To achieve chiral transfer from CNCs to PANI via a co-assembly method.
• To investigate the optical activity and chiroptical properties of the resulting CNCs/PANI composite films.
• To understand the role of CNCs' chiral nematic ordering in inducing chirality in PANI.

Main Methods:

• Co-assembly of cellulose nanocrystals (CNCs) and polyaniline (PANI) in an aqueous suspension.
• Fabrication of CNCs/PANI composite films.
• Characterization using circular dichroism (CD) spectroscopy to observe the Cotton effect and optical activity.

Main Results:

• Successful chiral transfer from CNCs to PANI was achieved for the first time, yielding optically active PANI films.
• The CNCs/PANI composite films exhibited a notable Cotton effect, attributed to polaron band transitions in PANI.
• The chiral nematic ordering of CNCs was found to be essential for chiral transfer, as the CD signal disappeared upon cholesteric phase collapse.

Conclusions:

• The co-assembly method effectively transfers chirality from CNCs to PANI, creating a helically stacked structure.
• The optical activity of PANI in the composite film originates from its long-range chiral organization templated by CNCs.
• This study demonstrates a novel approach to impart chirality to conducting polymers, opening avenues for chiral optoelectronic materials.