Effect of thermal treatments on chiral nematic cellulose nanocrystal films

The ability to manipulate the optical appearance of materials is essential in virtually all products and areas of technology. Structurally coloured chiral nematic cellulose nanocrystal (CNC) films proved to be an excellent platform to design optical appearance, as their response can be moulded by organising them in hierarchical architectures. Here, we study how thermal treatments influence the optical appearance of structurally coloured CNC films. We demonstrate that the CNCs helicoidal architecture and the chiral optical response can be maintained up to 250 degrees C after base treatment and cross-linking with glutaraldehyde, while, alternatively, an exposure to vacuum allows for the helicoidal arrangement to be further preserved up to 900 degrees C, thus producing aromatic chiral carbon. The ability to retain the helicoidal arrangement, and thus the visual appearance, in CNC films up to 250 degrees C is highly desirable for high temperature colour-based industrial applications and for passive colorimetric heat sensors. Similarly, the production of chiral carbon provides a new type of conductive carbon for electrochemical applications.

Automated summary

This study demonstrates how thermal treatments can influence the optical appearance of structurally coloured CNC films, and how to maintain their helicoidal architecture and chiral optical response in different conditions. Retaining the helicoidal arrangement in CNC films at high temperatures is crucial for industrial and sensor applications, while the production of chiral carbon offers new possibilities for electrochemical applications.