3D Printed Cellulose Nanocrystals with Controlled Dual Chiroptical Properties and Infra-Red Reflectance

Daylight management in buildings is increasingly important due to ongoing efforts to reduce energy consumption for heating and cooling. Current absorption-based technologies affect the visible spectrum, while near-infrared (NIR) reflecting materials, such as chiral nematic liquid crystals, often require crosslinking stabilization of synthetic mesogens, which can be undesirable in certain cases. In this work, we demonstrate development and manufacturing of a material with good visible transmittance that limits NIR interior irradiation, using abundant and renewable sources via an accessible method. Additionally, there is growing demand for materials with engineered circular dichroism for applications sensitive to circularly polarized light.<br/><br/>To address these needs, we produced twisted helical cellulose nanocrystal (CNC) films with dual chiroptical properties using a facile blade coating-based 3D printing method. With our top-down approach we assemble cellulose nanocrystals thin films of both handednesses. First, we assembled linearly oriented CNC monolayers via shear induced alignment. Then, engineered twisted Bouligand nanostructures were constructed via a sequential deposition technique by depositing each next layer in clockwise and counter-clockwise fashion by rotating the substrate at a fixed angle.<br/><br/>Material characterization was performed using atomic force microscopy, UV-Vis-NIR spectroscopy, ellipsometry, circular dichroism spectroscopy, and FDTD simulations. The films exhibited both left- and right-handed (LH, RH) chiroptical properties, unlike homochiral self-assembled CNC films. We demonstrate that by manipulation of the process parameters – rotation angle and layer thickness – distinct circular dichroism patterns and transmittance could be achieved. Furthermore, we show that the produced films could be treated as a hybrid between a 1D photonic crystal and a chiral nematic film, exhibiting both IR reflectance and circular dichroism peaks, resulting in a material with dual chiroptical properties.<br/><br/>The versatility of this desktop method also enabled the production of achiral films with NIR reflectance. These two cases demonstrate the potential of the top-down structuring of cellulose nanomaterials for chirality-sensitive photonic and energy management applications.