Polarization-Dependent Color Modulation in Electrodeposited Cellulose Nanocrystals and Birefringent Multilayers

Cellulose nanocrystals (CNCs) can self-organize into a chiral nematic liquid crystal phase with a left-handed helical arrangement, resulting in structurally intrinsic photonic properties in the dry state. These include iridescence and the selective reflection of left circular polarized light, where the wavelength is typically defined by the surface chemistry and charge of the CNCs before self-assembly. This work demonstrates how passive and dynamic stimulation can modulate the reflected wavelength across the entire visible light range. While the former is achieved through ion exchange at the CNC surface and electrophoretic deposition, the latter can be achieved by combining CNC layers with a thin-film heater. Further, the multilayer electrodeposited CNC films are combined with a birefringent polypropylene tape as a retardation plate to enable reflection of both left-handed and right-handed circularly polarized light (LCPL and RCPL, respectively). This architecture allows various colors in LCPL and RCPL channels to be obtained, depending on the number of layers and the initial photonic bandgap conditions of the CNC films, which will not be possible with regular self-assembled CNC films. The results obtained demonstrate the potential of CNC multilayer birefringent structures to be applied in photonics, imaging, sensing, and information processing.