Uncovering The Circular Polarization Potential And Application Of Cellulose Nanocrystal

Crystalline nanocellulose is a renewable nanomaterial.It exhibits the characteristics of high crystallinity,large specific surface area,excellent mechanical strength,surface modification and biocompatibility.More importantly,crystalline nanocellulose could self-assemble to chiral nematic liquid crystals in polar solvents.Since 2010,the research of crystalline nanocellulose-based photonic crystal materials has received extensive attention.The research works mainly include(1)constructing self-supporting organic and inorganic chiral photonic crystal films and exploring chiral transfer and new physical and chemical phenomena using crystalline nanocellulose as a template,(2)sensing-ability of cellulose-based chiral photonic crystal film,(3)the application of cellulose-based chiral photonic crystal films in asymmetric catalytic and chiral separation,(4)cellulose-based biomimetic structural materials.However,the circular polarization ability and application potential of cellulose-based chiral nematic liquid crystals have rarely been reported.The generation,regulation and application potential of circularly polarized light are important scientific propositions in the fields of physics,chemistry,materials,and even biomedicine,and have important theoretical and practical values for the development of photonic technology.However,the research and development of circularly polarized light materials still face challenges.In this context,this thesis focuses on the circular polarization capability of crystalline nano-cellulose chiral nematic liquid crystals.For the first time,the intrinsic circularly polarized light ability and the circular polarization fluorescence ability of the crystalline nano-cellulose membrane were revealed.The regulation mechanism of the photon forbidden band,film thickness,and the intensity of spontaneous radiation on circularly polarized light intensity and waveband were proposed and proved.With the integration of structure control,the full-silica circularly polarized light film material was obtained for the first time.The application potential of cellulose-based circularly polarized light film materials in the fields of anti-counterfeiting,chiral recognition,and chiral switches was exhibited for the first time.Taking advantage of evaporation-induced assembly and nanovoids of intrinsic structure,a series of high-performance cellulose-based circular-polarized fluorescent composite film materials were designed and built,providing new territory for the large-scale production of circularly polarized light material with accurate chirality,high intensity and adjustable wavelength band.This thesis consists of six chapters.The first chapter is the introduction,expounds the basic properties and the current research status of crystalline nanocellulose and also expounds the intention of this thesis.Chapter 2 focuses on the intrinsic circular polarization capability of crystalline nanocellulose chiral nematic liquid crystal film.The intrinsic chiral optical properties of the liquid crystal structure of the crystalline neutro-nanocellulose have been revealed for the first time by selectively reflecting left circularly polarized light and transmiting right circularly polarized light when the normal incident light matches its forbidden band.The forbidden band of the left-hand nematic phase of this liquid crystal is adjustable in the near-ultraviolet to near-infrared wavelength range.Therefore,it can decompose ordinary incident light of any wavelength within the waveband range into left and right circularly polarized light.The intensity of circularly polarized light is very high and the value of the anisotropy factor is as high as 0.87.The application potential of crystalline nano-cellulose L-nish nematic liquid crystal films for chiral recognition of circularly polarized light was demonstrated.The research results lay a foundation for the development of new material and application of crystalline nanocellulose-based circularly polarized light.In the third chapter,the circular polarization fluorescence capability of crystalline nanocellulose-based chiral nematic liquid crystal composite films was demonstrated.The experimental results show that the composite film converts the spontaneous emission of its overlap with the forbidden band into right-handed circularly polarized fluorescence.The complete overlap of the spontaneous emission and the forbidden band results in the strongest right-handed circularly polarized fluorescence,and the band edge effect enhances the right-handed circular polarization fluorescence.In theory,the photon forbidden band effect on the asymmetry factor and the wave band is explained.The application potential of cellulose-based membrane materials in the field of circular polarization anti-counterfeiting was demonstrated for the first time.In the aqueous nanocrystalline cellulose solution,single or multiple fluorescent guest with different charge and molecule to nanometer scale were doped,and the chiral nematic liquid crystal composite film was obtained by evaporation-induced co-assembly.The results of this chapter provide a broad-spectrum chiral entity for the development and mass production of renewable,inexpensive,highly adjustable,circularly polarized fluorescent nanomaterials.In the fourth chapter,we further explored the right-handed circular polarization fluorescence characteristics,regulation mechanism and application potential of cellulose-based chiral nematic composite membrane.Selecting achiral carbon dots as fluorescent guest,a carbon-doped circularly-polarized fluorescent nanomaterial was firstly realized.The effects of film thickness,fluorescence intensity,and guest electrical properties on the circularly polarized fluorescent intensity were revealed at experimental data and theoretical levels,and multicolor adjustable right-handed circularly polarized fluorescence with an asymmetric factor peak of-0.74 were obtained.In experiments,the effect of the forbidden effect on the circular polarization fluorescence intensity was further demonstrated.Chapter 5 describes the construction and application potential of full-silica circularly polarized fluorescent materials.Using crystalline nanocellulose as a template,cellulose/silica chiral nematic liquid crystal composite films were obtained by evaporation-induced co-assembly and mineralization.Calcining conditions are controlled to remove cellulose and produce defective fluorescence and phosphorescence.The forbidden band position was adjusted to obtain a mesoporous silica chiral nematic liquid crystal film having the ability to convert its defect fluorescence into right-handed circular polarization fluorescence.A full-silica circularly polarized fluorescent material was obtained for the first time,and its long phosphorescent lifetime was explained.The preparation method is simple,no additives,no complicated process,no expensive chemical reagents,zero excreta,and easy scale production.The obtained silicon dioxide film has chiral nematic structure,defect state light emission,phosphorescence,and mesopores at the same time.The application potential of silicon dioxide films in the field of circularly polarized fluorescent light was demonstrated.The sixth chapter is the summary and outlook of the thesis.