Fig. 1. Mixing glutaraldehyde with CNC and inducing self-assembly through evaporation to form independent thin films^［22］

Fig. 2. Schematic diagram of a left-handed chiral nematic rainbow film formed by chiral CNC.（a）Natural trees；（b）Cellulose microfibrils composed of crystalline and amorphous regions；（c）CNC nanorods were achieved by acid hydrolysis process；（d）Self-assembly process of CNCs；（e）Schematic diagram of the variation in half­helical pitch of CNCs derived from coupled sulfuric acid and acrylic acid hydrolysis compared to that derived from sulfuric acid hydrolysis，showing an obvious left­handed helical structure. “P” represents the helical pitch；（f）A clear red shift of the iridescent color in the CNC films observed with the polarized optical micrograph（scale bar：2 µm）^［23］.

Fig. 3. Scanning electron microscopy images of chiral nematic mesoporous silica.（a）Cross-sectional view of CMO3 at high magnification reveals a left-handed chiralnematic structure (scale bar=1 μm). The arrow indicates a 180° counter-clockwise rotation of the director, i.e., one-half helical pitch.（b）Crosssection of CMO1 reveals long-range ordering with an average helical pitch of 290 nm (scale bar=2 μm).（c）Cross-section of CMO4 reveals longrange ordering with an average helical pitch of 510 nm (scale bar=2 μm)^[33].

Fig. 4. Scanning electron microscopy images of chiral nematic mesoporous organosilicas.（a）Me-CNMO；（b）Prop/Et-CNMO；（c）But/Et-CNMO；（d）Pent/Et-CNMO；（e）Hex/Et-CNMO；（f）Urea/Et-CNMO^［39］.

Fig. 5. Synthesis of the mesoporous chiral nematic phenol-formaldehyde（PF）resins. CNC dispersion is mixed with an aqueous solution of the PF polymer precursor and cured to achieve chiral nematic composite films（CP）. The most of the CNC template is removed by alkaline treatment. The highly iridescent，mesoporous photonic resins（MP）is achieved after supercritical drying.

Fig. 6. （a）Preparation of cellulose nanocrystals/polyethylene glycol composite materials with chiral nematic structure；（b）Transmission spectra of neat CNC-2 and the CNC-2/PEG composite films with reflectance peaks in the ultraviolet and visible spectrum；（c）CNC-2 and CNC-2/PEG composite films exhibiting different structural colors under white light irradiation；（d）SEM images for the side view of the cracked neat CNC-2 and the CNC-2/PEG composite films showing the helical pitch distance；（e）Images of NC-2 and CNC-2/PEG composite films captured using cross polarized light microscopy galvanometer^［14］.

Fig. 7. Optical properties of chiral nematic composite thin film materials and their prepared mesoporous photonic cellulose thin films.（a）Photograph（top）and SEM image（bottom）of the composite film CNC-UF-A4 after curing；（b）Photograph（top）and SEM image（bottom）of MPC（mesoporous photonic cellulose）air-dried from H₂O；（c）Photograph（top）and SEM image（bottom）of MPC dried from EtOH with supercritical CO₂^［45］.

Fig. 8. Chiral mesoporous silica materials used as stationary phases for capillary gas chromatography to separate chiral drugs^［47］