Regulation Of Structure Color And Optical Properties Of Cholesteric Liquid Crystal Phase Based On Nanocrystalline Cellulose

Nanocrystalline cellulose(NCC),as an important derivative of traditional cellulose,is considered to have broad application prospects in the fields of nano-assembled materials,new optical materials,and functional composite materials,due to its attributes of large reserves,renewability,and easy preparation as well as its performance features of high Young's modulus,high light transmittance,high stability,and high biocompatibility.In this paper,using cotton as raw material,rod-shaped NCC was prepared by sulfuric acid hydrolysis.The structure,morphology and surface properties of the prepared NCC was analyzed,and then cholesteric liquid crystal cellulose with birefringence was prepared.At the same time,the influence of the external environment on the self-assembly behavior of NCC was explored in this paper,and magnetic-vacuum synergistic regulation method was designed to achieve the local regulation of the cholesteric liquid crystal phase of cellulose.In addition,the preparation of rare earth upconversion nanomaterials with different morphologies was explored,and the cholesteric liquid crystal cellulose and upconversion nanomaterials were composite,and the effect of cellulosic cholesteric liquid crystal on upconversion fluorescence was explored,as well as the application of this kind of composite materials in the field of anti-counterfeiting.The main research contents are as follows:Using cotton as raw material,NCC suspension was prepared by sulfuric acid hydrolysis,and the morphology,structure and surface properties of the prepared NCC were characterized.The prepared NCC was rod-shaped particle,XRD results demonstrated that the NCC of sulfuric acid hydrolysis preparation was cellulose-I type structure.Zeta potential and laser particle size analyzer analysis showed that the average particle size of NCC was about 161.6 nm,and its surface charge was-40.9 mV.At the same time,analyses of the cellulose film prepared by self-assembly confirm that the prepared cellulose has significant birefringence,obvious fingerprint texture,and a microscopic morphology of cholesteric structure with a left-handed normal helix.Meanwhile,based on the high aspect ratio,negative surface charge,and rigidity of NCC obtained by acid hydrolysis,the entire formation mechanism of NCC self-assembly to prepare cholesteric liquid crystals was explained.In addition,it had been confirmed that cholesteric cellulose had strong application potential in the field of humidity response.Based on the self-assembly characteristics of NCC,the influence of different vacuum conditions on the behavior of NCC self-assembly to prepare cholesteric cellulose was explored.The results showed that when environmental pressure of the self-assembly process was reduced,the wavelength of the reflected light of cholesteric cellulose exhibited a significant red shift.Then,based on the afore-mentioned self-assembly behavior,the effect of the same magnetic field on cholesteric cellulose under different vacuum conditions was explored.It was found that a magnetic field with a magnetic field intensity of about 0.3T could affect the self-assembly properties of the cholesteric liquid crystal phase of cellulose in the region and produced a faint blue and blue-green difference from the surrounding.However,as the vacuum degree increased,the ability of the magnetic field to act on cholesteric cellulose gradually increased.Specifically,when the vacuum degree of the cellulose film increased from 0 to 0.08,the reflected light wavelength of the cellulose directly affected by the magnetic field shifted from 348 nm to 419 nm,which is a regular red shift.Based on this,this article explored the local regulation ability of the magnetic field-vacuum synergy on cholesteric fibers.The results showed that the pitch of the area affected by the magnetic field-vacuum synergy was about 240 nm and the pitch of the surrounding area was 210 nm.The magnetic-vacuum synergy achieved local effective regulation of cholesteric cellulose.NaBiF4:Yb3+,Er3+and NaGdF4:Yb3+,Er3+nanoparticles with hollow structure,branched structure and spherical structure were prepared by coprecipitation,hydrothermal and solvothermal methods,and then mixed with the NCC solution prepared by sulfuric acid hydrolysis.The chiral cellulose films were prepared by co-assembly.It was found that the spherical NaGdF4:Yb3+,Er3+,with isotropic,small nanometer particle size and uniform dispersion,combined with NCC best,and the prepared films with obvious structure color show distinct circularly polarized light.More interestingly,it was found in the experiment that by using the aforementioned magnetic field-vacuum coordination to induce and adjust the band gap structure of the chiral film,the improvement of the upconversion luminescence performance of NaGdF4:Yb3+,Er3+by one-dimensional photonic crystals was about 2.7 times.Subsequently,the prepared NaGdF4:Yb3+,Er3+/NCC cholesteric composite film with up-conversion luminescence performance was used for anti-counterfeiting,which further illustrated that cellulose had extremely high application potential in new optical functional materials.And cellulose is expected to be an important part of the high-value utilization of agricultural and forestry biomass.