Composite Cholesteric Nanocellulose Films with Enhanced Mechanical Properties

Cellulose nanocrystals (CNCs) form cholesteric films that exhibit birefringence, iridescence, and circular dichroism; however, these films are brittle and prone to cracking. Here we report composite cholesteric films formed from CNCs and soft reactive latex nanoparticles (NPs) (the latter underwent in situ cross-linking during film formation). Composite films exhibited a self-stratified morphology, with lateral cholesteric CNC-rich layers and isotropic latex NP-rich layers. The films retained their photonic properties and exhibited significantly enhanced mechanical properties. In comparison with latex-free CNC films, composite films had an similar to 60% higher toughness but did not compromise their tensile strength. The combination of photonic performance and improved mechanical properties of the composite nanocellulose films expands the range of applications of these materials for the fabrication of optical devices.