Chiral nematic assemblies of silver nanoparticles in cellulose nanocrystal membrane with tunable optical properties

Cellulose nanocrystals (CNCs) possessing chiral nematic structures have been developed as liquid crystal templates for optical materials and devices. These templates provide materials with advanced structural and optical properties, leading to numerous promising discoveries of new functional materials. In this work, the chiral nematic CNC/silver nanoparticles (CNC/AgNPs) composite membranes were prepared and displayed striking iridescent colors. The addition of AgNPs strengthened the chiral structure of CNC-based composites by adjusting the pitch of the chiral nematic structure. As the AgNPs content decreased from 8 to 2 wt%, a redshift of the reflection wavelength was observed from 475 to 773 nm, and the distance between the two adjacent layers of the membrane increased from 155 to 254 nm, according to a fitted linear function. Therefore, this composite membrane exhibited excellent chiral optical properties, and the chiral reflectance could be tuned accurately by regulating the content ratio of CNCs to AgNPs. New insights into designing advanced functional optics were provided, herein to show their potential applications, such as in smart windows and anti-counterfeit labels.