Double Bouligand Printed Twisted Stacks: Mirrored Chiroptical Polarization and Enhanced Compressive Mechanics

Abstract Cellulose nanocrystals, a type of needle‐like polysaccharide nanomaterial, self‐assemble into left‐handed helical stacks showing selective optical reflection with visible‐range photonic bandgap and distinct circular polarization due to left‐handed twisted organization, called Bouligand structure, with a pitch length of several hundreds of nanometers. In contrast, this work presents peculiar printed thin films of shear‐oriented twisted cellulose nanocrystals with controllable hierarchical structures for mirrored optical response through the tailoring of the non‐traditional double Bouligand architecture. The free‐standing films exhibit mirrored circular dichroism and show complex optical activity with alternative polarization components, such as linear and circular birefringence that are very different from traditional self‐assembled organization. Furthermore, this unique synthetic double Bouligand structure shows increased mechanical robustness to compressive stresses and indentations along with enhanced elastic recovery. These results offer a scalable processing method to produce unique on‐demand thin bio‐derived chiroptical films with a unique optical signature with high mechanical robustness for laser actuation, optical encryption, and chiroptical sensors.