Preparation Of Nanocomposite Optical Films With Controllable Refractive Index

As one important part of modern society, optical materials are widely used inmilitary, traffic and daily life. People pay more attention to special refractive indexmaterials in different kinds of optical materials. Refractive index is an importantcharacterization of materials. Traditional method of preparing special refractive indexmaterials is to process inorganic or organic (polymer) materials. Inorganic materialsshow high stability and excellent optical performances, but the complexity of processrestricts the appliance. Although impact resistance and convenience of process oforganic (polymer) materials are better than inorganic materials, stability and opticalperformances of inorganic materials are slightly worse. So hybrid materials come intobeing because they integrate the advantages of inorganic and organic (polymer)materials.There are many difficulties to prepare high optical performance materials withspecial refractive index. For low refractive index hybrid materials, traditional etchingmethod limits the size of the production and increases the costs first. And secondcommon low refractive index inorganic particles are easy to aggregate in polymer anddecrease the transmittance of the hybrid materials. Finally mechanical stability oftraditional low refractive materials is poor due to porous structures. For high refractive index hybrid materials, on one hand, people try to synthesis high refractive indexpolymer, but most of polymers contain benzene rings or conjugation structures whichmay decrease the transmittance of materials. On the other hand, people attempt tointroduce modified inorganic particles with high weight content to increase therefractive index. However, too much ligand will decrease the refractive index of hybridmaterials and high weight content nanoparticles may increase the possibility ofaggregation between nanoparticles. In summary, it is an important issue to preparehybrid materials with high performance optical materials.In this dissertation, transparent hybrid optical films with special refractive indexwere prepared by incorporating nano-materials into organic sol and polymers byblending method. The work doesn't broaden the method of preparing nanocomposites,but also have potential application in fabricating optical materials with special refractiveindex.In chapter one, we summarized the development and outlook of low refractiveindex hybrid materials and high refractive index hybrid materials respectively, andillustrated the high refractive index materials in the actual applications.In chapter two, we used simple method to prepare low refractive index, antifoggingand mechanical stable films doped with mesoporous SiO₂nanoparticles. The size ofnanoparticles prepared in neutral buffer solution is130nm. We dispersed themesoporous SiO₂nanoparticles containing surfactants into the ethanol and blended withsilica sol. We obtained the multifunctional optical films by spin-coating the hybrid soland calcinated to remove the surfactants. The preparation method has advantages asfollows: For one thing, mesoporous SiO₂nanoparticles containing surfactants candisperse in ethanol and silica sol without any aggregation. It can avoid complexchemical modification of mesoporous SiO₂nanoparticles first of all. The next it breakthrough the limitations that hybrid materials doped with unmodified mesoporous SiO₂nanoparticles can only be obtained by LBL method. Finally, the process of removing thesurfactants after solidification of the films can prevent organic sol diffusing into the porous structure and decreasing the air ratio. For another, mesoporous SiO₂nanoparticles embed in the silica film and increase the mechanical stability of the hybridfilms. With the increase of the mesoporous SiO₂nanoparticles weight content, therefractive index of the films decrease and the films show more better performances ofantireflective and antifogging. When the weight content of mesoporous SiO₂nanoparticles was6%, the refractive index of the film was1.24, the transmittance of thefilm was about99%, and the spreading time of water droplet was about158ms.Performances of low refractive index, antireflective and antifogging maintained wellafter the films were scratched repeatedly by weight loaded steel wool and filter paper.In chapter three, we prepared high refractive index transparent hybrid films byintroducing modified commercialized crystalline silicon nanoparticles into sol andpolymers. Modified crystalline silicon nanoparticles could disperse in organic solventsand mixed solvent of solvent and monomer. The dispersion of crystalline siliconnanoparticles was improved after modification, and the crystalline structure kept aftermodification. Crystalline silicon nanoparticles could increase the refractive index of thehybrid films effectively in the premise of high transparent. When the weight content ofcrystalline silicon nanoparticles was10%, the refractive index of c-Si/TiO₂hybrid filmwas about1.957. AFM images showed the surfaces of the films were flat and the phaseswere uniform. The transmittance of the film was about80%. We also prepared highrefractive index c-Si/SiO₂and c-Si/PVA hybrid films. Moreover, we modifiedcrystalline silicon nanoparticles with KH-570and made it polymerized with DMAAunder ultraviolet irradiation. When the refractive index was about1.990andtransmittance was about76.5%with nanophase content of25wt%.In chapter four, we synthesized monolayer graphene oxide and modified grapheneoxide to make it stable in organic system. We prepared graphene/TiO₂hybrid films byreducing the hybrid film of graphene oxide and TiO₂with hydrazine hydrate. Therefractive index of the film could be continuously regulated in the range of1.849–1.908by the content of graphene. The transmittance was above75%when the graphene was15wt%. Furthermore we also prepared graphene/polyurethane hybrid films. Therefractive index of the film increased with the weight content increase of graphene, andthe increase is a linear relationship. TEM images showed graphene was monolayer inthe nanocomposites, it is important for transparent hybrid films. The transmittance ofthe films was higher than85%when graphene is25wt%.