Self-assembly Of Cellulose Nanocrystals,Property Regulation And Templating Effect

Cellulose nanocrystals?CNCs?can be extracted from natural cellulose fibers by strong acid hydrolysis,and are highly crystalline rigid nanoparticles with rod-like or needle-like shapes.The chiral structure of CNCs and the characteristics of evaporation induced self-assembly?EISA?have given it broad prospects for development in the field of special functional nanomaterials.According to the current research status,CNCs can not only be assembled with substances with good compatibility,to explore their functional applications by adjusting their chiral nematic phase structure,but also can be assembled with CNCs and other composite substances,and then through the sacrificial template method?for Nanocellulose undergoes alkaline hydrolysis and calcination to remove?,construct chiral nematic mesoporous organic,inorganic and carbon materials to make full use of ordered mesoporous for modification,catalysis and adsorption to form a composite superposition of optical and other multiple functions.In this paper,the self-assembly characteristics of cellulose nanocrystals are mainly studied in the following aspects:1. N-methylmorpholine-N-oxide?NMMO?modified cellulose nanocrystal film structure and properties control. NMMO aqueous solution is an excellent cellulose solvent.The self-assembled film of pure CNC is modified with NMMO to obtain N_x-CNC film.NMMO will cause the CNC film to swell,causing its reflection wavelength to redshift.The swelling effect is due to the fact that NMMO can penetrate into the crystalline region of a single CNC crystal,and secondly,it can be inserted between CNC nanorods.After removing NMMO,the pitch of the film will be reduced,the blue shift of the reflection wavelength will be induced,and the color of the CNC film will return to the original blue.The N_x-CNC film has a humidity-responsive performance and can exhibit reversible color changes within a few minutes.The increase in NMMO content will also expand the wavelength range of the color response of the CNC film.In addition,the NMMO solution can also be used as"ink"to inscribe an optical pattern with a humidity response on the CNC film.2. Preparation and structure of chiral nematic porous cellulose nanocrystal aerogel.The NMMO modified CNC film?N_x-CNC?as described above was immersed in absolute ethanol to remove NMMO.Firstly,it was verified by ultraviolet-visible spectroscopy.During the removal of NMMO by immersion,anhydrous ethanol did not cause the CNC film to expand or contract,thus ensuring that the film could maintain the original voids.After drying with supercritical CO₂,a porous aerogel with chiral nematic structure?EN_x-CNC?was obtained.The N₂ absorption-desorption test and scanning electron microscope test show that the EN_x-CNC after drying has a mesoporous structure,and the material still maintains the original chiral nematic phase structure.3. Construction and property control of broadband reflective nanocellulose composites.The thermosetting polyurethane and nanocellulose were slowly evaporated and self-assembled to prepare a composite optical film with heterogeneous structure.Experiments show that during the slow evaporation process,polyurethane particles can hinder the normal fusion of CNC,thereby destroying the original stacking arrangement of nanocellulose,and causing the CNC to assemble into a chiral nematic liquid crystal structure with an inclined angle.Compared with the normally assembled CNC film,the change in the direction of the spiral axis in the nanocrystalline cellulose assembly domain eventually led to broadband chiral reflection.