Processing Parameter-Performance Nexus in 3D Printing of Nanostructured Chiral Photonics

Precisely crafted hierarchical architectures found in naturally derived biomaterials underpin the exceptional performance and functionality showcased by the host organism. In particular, layered helical assemblies composed of cellulose, chitin, or collagen serve as the foundation for some of the most mechanically robust and visually striking natural materials. By utilizing structured materials in additive manufacturing techniques such as extrusion-based 3D printing, the intrinsic deformation process can be used to implement bottom-up design of printed constructs, offering the potential to create intricate macroscale geometries with embedded nanoscale functionality. In this study, comprehensive rheological and rheo-optical characterization of structurally colored, photocurable liquid crystalline inks based on hydroxypropyl cellulose (HPC) are carried out to define the structural dynamics of the system under flow and following flow cessation. It is shown that the processing parameters selected for 3D printing can induce order or disarray in the extruded ink's liquid crystal nanostructure. Low to intermediate shear rates order the chiral nematic domains to yield intense structural color. In contrast, high shear rates induce elastic instabilities that diminish the filament's photonic quality. After establishing the processing parameter-nanostructure relationship, the curing kinetics of these photocurable inks are tailored to facilitate the arrest of the liquid crystalline structure.