Mind the Microgap in Iridescent Cellulose Nanocrystal Films

Researchers reported a new cellulose-based photonic structure, which reflected both right circularly polarized (RCP) and left circularly polarized (LCP) light that can be tuned by temperature variation and the application of an external electric field. The optical properties of the cellulose nanocrystal (CNC) samples were investigated both in terms of their microstructure by scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS) and spectroscopically, using circularly and linear polarized light coupled with a polarized optical microscope (POM). The nanocrystals used in this work were prepared by acid hydrolysis of microcrystalline cellulose. Aqueous suspensions of CNCs in the acid form were used, resulting in freestanding iridescent films after drying with colors depending on the viewing angle.