Conformal assembly of cellulose nanocrystals with micro-nano structures for structural color

Cellulose Nanocrystals (CNCs) are nanoscale, rigid rod-shaped cellulose fibers, measuring 100-500 nm in length, 2-20 nm in diameter, and with aspect ratios ranging from 5-100. At concentrations below a critical threshold (Critical Concentration I), CNC suspensions maintain isotropic characteristics. Upon surpassing another threshold (Critical Concentration II), the suspension transitions to an anisotropic phase, spontaneously forming chiral nematic structures. These chiral configurations are preserved even after drying the CNC suspensions. CNC photonic films exhibit the optical attributes of chiral nematic liquid crystals, including selective reflection and polarization, which manifest as pronounced structural colors and circular birefringence. This research demonstrates the structure color of CNCs through the conformal assembly with micro-nanostructures. By assembling CNCs at a 0.1 wt% concentration with triangular micro-nanostructures of varied sizes, the resulting structures displayed enhanced polarization characteristics. The conformal assembly technique introduced in this study is pivotal for advancing CNC-based photonic devices, opening new avenues in the realm of optoelectronic and environmentally friendly nanomaterials. These developments hold considerable potential for applications in optical filters, sensors, visual identifiers, and color display technologies.