Multifunctional chiral nematic cellulose nanocrystals/glycerol structural colored nanocomposites for intelligent responsive films, photonic inks and iridescent coatings

Structural colored nanocomposites with photonic liquid crystal structures are desirable owing to their excellent optical performances, unique structural features and intelligent responsive behaviors. Herein, a series of cellulose nanocrystal (CNC)-based nanocomposite materials that mimic the cholesteric structural colored creatures in nature were prepared and their functional applications investigated. Multicolored, flexible and intelligent responsive iridescent films were constructed by mixing cellulose nanocrystals (CNCs) and glycerol (Gly) in different ratios. Consequently, redshifted structural colors were obtained from the increase in the helical pitch of the chiral nematic structures according to the microstructure analysis. In addition to improving the mechanical properties of the composite films, glycerol also promoted the crystallinity of the films to different degrees. The CNC/Gly20 films exhibited reversible reflection colors at different relative humidity because of the strong water absorption capability of glycerol. Furthermore, CNC/Gly composite suspensions were used as photonic inks to obtain photonic writing with unique fingerprint textures. Moreover, the CNC/Gly nanocomposites were also used to make iridescent coatings on different substrates. The incorporation of glycerol improved the compatibility between the interfaces. Thus, photonic nanocomposites from cellulose nanocrystals can potentially be developed as optical sensors, security markings and functional coatings.