Properties And Applications Of Cellulose-based Fluorescent Composite Films

With the rapid development of nanotechnology,cellulose nanocrystals(CNCs)have become a new star in nanomaterials.Due to their large specific surface area,strong hydrophilicity,good thermal stability and easy functionalization,CNCs show great potential in many fields.Moreover,CNCs are chiral and dispersion-stable,and can be evaporation-induced self-assembly(EISA)into left-handed chiral nematic liquid crystals(LC)under strictly controlled processing conditions.CNCs chiral helical structure produced by EISA has a special birefringence phenomenon and selective reflection of polarized light.Hence,CNCS is a kind of excellent photonic crystal,which can be used in the field of photon sensing.Based on the chiral nematic phase structure and co-assembly characteristics of nanocellulose,this paper focuses on the following two aspects:First,Photoluminescence-enhanced of cholesteric thin films:co-assembling of copper nanoclusters and cellulose nanocrystals.In this work,GSH-CuNCs were encapsulated into CNC with chiral nematic phase structure by co-assembly strategy,and composite films with structural color and fluorescence were prepared.The PEG-CNCS-GSH-CuNCs fluorescent color composite films showed wide band reflection due to the difference of helix spacing.Two emission peaks were observed at 439 nm and 600 nm,which were induced by crystallization of CNCs and assembly of CuNCs,respectively.In this study,we found that the fluorescence intensity and lifetime of the composite films were enhanced,and we proposed a mechanism of assembly induced emission of GSH-Cuncs in CNC films,which was attributed to the confining effect of the composite films and the associated molecular interaction.Subsequently,it was found that the emission color and intensity of CuNCs could be changed by adjusting the reaction time,reaction temperature and p H of the solution.Under the appropriate concentration of GSH and Cu²⁺,the chiral structure of GSH-CuNCs can make the CNC composite film show dextral chiral fluorescence with an asymmetry factor of-0.16.Based on the above characteristics,light-emitting diodes(LEDs)with different emission colors were fabricated by using light-emitting composite films.In addition,we designed light-emitting patterns with anti-counterfeiters on PEG-CNC-GSH-Cuncs films,such as a specific logo,a panda and a flower.Second,dextral chiral luminescent films were prepared by co-assembly of nano-cellulose and quantum dots.Nano-sized quantum dots(CDs)tend to aggregate,which leads to aggregation fluorescence quenching(ACQ).To suppress the self-assembly of CDs,we embedded the CDs prepared by hydrothermal synthesis into the CNCs to obtain the CNCs-CDs composite film by evaporation-induced co-assembly.The experiments show that CNCs can limit CDs aggregation due to the presence of electrostatic forces.At the same time,CDs was loaded onto the film by co-assembly,and the fluorescence intensity of the film was enhanced,and the film had good chiral fluorescence.