Study On Preparation And Properties Of Quantum Dots Film Based On Polymer Dispersed Liquid Crystals

As the down-conversion materials for display devices,quantum dots(QDs)are usually encapsulated into the transparent polymer matrix such as polystyrene(PS)or poly(methyl methacrylate)(PMMA)to form QDs films.However,the efficiency of the emitting light output and utility ratio of incident/excitation light are drastically reduced by the light wave-guide structure and high transmittance of the film itself,respectively.The scattering state of liquid crystals/polymer composite films allows the emergence of multiple scattering of incident light,which was confirmed to effectively achieve the enhancement of fluorescence and modulation of quantum dots.In addition to this,quantum dot films based on liquid crystals/polymer system also possess the benefits of relatively simple manufacturing process,cost-efficiency and potential of large-area commercialization.In order to break the limitations of the substrate-dependence and limited quantum dot encapsulating properties of QDs film based on liquid crystals/polymer system and expand the application,an all-polymerization QDs film based on polymerizable liquid crystal/polymer system was developed in succession.Free-standing,fluorescent enhancement and excellent encapsulation property of QDs are the highlights of the unique film.This thesis focused on the molecular design,synthesis,characterization and molecular simulation of polymerizable liquid crystals monomers as well as the preparation and properties of substrate-dependence QDs film based on the liquid crystals/polymer system,which enabled to realize the fluorescence enhancement and modulation of QDs.Moreover,the preparation and properties of of free-standing all-polymerization QDs film based on the polymerizable liquid crystals/polymer system,which enabled to realize fluorescence enhancement and encapsulation of QDs,were also systematically investigated.The main research contents and conclusions are as follows:(1)Homologous series of hydroxyl,acryalte,and vinyl-ether terminated cyanobiphenyl compounds were designed and synthesized,which were respectively named as nOCB-OH,nOCB-AE and nOCB-VE(n=2-12),followed by structural determination,confirmed,property characterization of liquid crystals,investigation of odd-even effects and molecular simulation based on B3LYP/6-31G*theory level.Specifically,the introduction of environmentally friendly and highly efficient catalyst,[Ir(cod)Cl]2,provided a novel solution for the synthesis of vinyl-ether terminated cyanobiphenyl compounds.The results showed that the introduction of hydroxyl,acrylate or vinyl-ether terminated groups destabilized the SmA phase and therefore disappeared.The nematic phase existing in most compounds of homologous nOCB-OH and nOCB-VE series whereas the majority of homologous nOCB-AE compounds were crystalline.(2)The TiO2 nanoparticles with strong scattering were introduced in the QDs films based on polymer/TiO2,liquid crystals/polymer,and liquid crystals/polymer/TiO2 composte systems,respectively,and a comparative study of the three systems was conducted for a better evaluation of fluorescence enhancement and modulation of QDs films based on liquid crystals/polymer composite system.Additionally,effects of particle size,content and modification of TiO2 nanoparticles towards morphologies,electro-optical,fluorescence and mechanical properties of the QDs films were systematically investigated.The results suggested a 6-fold fluorescence enhancement of the QDs film based on the liquid crystals/polymer/TiO2 system with 150 nm particle size and 0.1 wt%loading content,comparing to regular,transparent acrylate polymer QDs film.(3)In order to systematically investigate the fluorescence enhancement and encapsulation properties of QDs film based on the polymerizable liquid crystals/polymer system,polymer dispersed vinyl-ether liquid crystals(PDVLC)and polymer dispersed crosslinked vinyl-ether liquid crystals(PDCVLC)as well as fluorine-containing polymer dispersed crosslinked vinyl-ether liquid crystals(F-PDCVLC)composite QDs films were prepared in succession by dual step polymerization of the(fluorine-containing)acryalte monomers radical polymerization and the vinyl-ether liquid crystals monomers cationic polymerization in this research.The results demonstrated that the F-PDCVLC composite QDs film enabled to realize a 5-fold fluorescence enhancement relative to that of the conventionl acryalte polymer QDs film and possessed excellent encapsulation properties of QDs.