Efficient preparation of cellulose nanocrystals and regulation of cholesteric liquid crystals for advanced anti-counterfeiting

Cellulose nanocrystals (CNCs) can self-assemble to form cholesteric liquid crystal, which make it one of the most promising optical materials at present. CNCs can be produced by sulfuric acid hydrolysis. It is found that hydrolysis conditions influence the existing form of reaction components and their reaction activities, which leads to different reaction routes and mechanisms under varied reaction conditions, with CNCs of varied quality produced. High-quality CNC with more uniform particle size could be prepared at a critical acid concentration of 64 wt%, which was used to study the formation process of CNC liquid crystal and the structure regulation of cholesteric liquid crystal. By adjusting the drying temperature and adding a small molecule of water-soluble chitosan (WSC) can well regulate cholesteric liquid crystal and change the pitch of a film, and the reflection wavelength can be redshifted, thus enriching texture patterns and creating distinctive color. Suitable addition of WSC can enhance the multi-domain effect during liquid crystal formation process and finally creates more colorful film with fine texture. The rich and tunable liquid crystal characteristics endowed by WSC addition is irreplicable and artistic, which helps to realize the great potential application of the composite film in advanced anti-counterfeiting. The formation process of CNC liquid crystal prepared by the sulfuric acid method was studied, and the structure of CNC cholesteric liquid crystal was adjusted by changing the drying temperature or mixing with small molecule water-soluble chitosan according to different regulatory mechanisms, and was applied in the field of anti-counterfeiting. image