| Cellulose is the most abundant biopolymer in the world and plays a critical role in human history such as construction,paper manufacture,clothing technology and so on.Until the last decades,it has revealed that cellulose acts as a functional material for photonic applications.Cellulose nanocrystals(CNCs)from native cellulose exhibit high birefringence,and could also assemble into nematic and cholesteric phase liquid crystals.The most remarkable properties of CNCs is that the liquid crystal configuration can be reserved in the dried film after drying processes,offering a robust template in assembling nanoparticles.Abundance,low-cost,diverse orientations,and stability of cellulose liquid crystal nanostructures attract various interest in novel optoelectronic nanomaterials and devicesThis thesis studies the cellulose liquid crystals-based optoelectronic nanomaterials and devices,including the phase behaviors of cellulose liquid crystals,optical CNC waveplates and silver nanowire-CNC compound optoelectronic materialsFirst,this thesis studies the phase beahviors of cellulose liquid crystals.CNCs produced by acid hydrolysis,could form the well-known cholesteric phase liquid crystals,and also form the nematic liquid crystals,where the mechanism involved in the formation of chiral helicoidal liquid crystal orderientation has been the subject of a vigorous discussion.The pH and concentration dependence of the CNC liquid crystals is studied using CNC liquid crystals droplets surrounded by silicone oil,allowing for convenient real-time microscale manipulation of its phase behaviors and properties.We observe the existence of nematic phases at both low and high pH regions that is consistented with the Stroobants-Lekkerkerker-Odijk theory.In addition to the well-known CNCs,we also prepared the novel discotic cellulose nanoparticles that exbihit the ability of self-assembling into nematic phase liquid crystals.Second,this thesis stduies the the alignment of nematic CNC liquid crystals and its application in optical waveplates.Nematic CNC liquid crystals doped with polyethylene glycol are aligned on patterned substrates on large scale by shearing forces and prepare CNC waveplates The optical performance of the CNC waveplates is investigated by Mueller matrix and examined by measuring the transmission spectra of the waveplate between two polarizers,where the optical extinction of CNCs is also extracted from the measured spectra.To overcome the wavelength dependent phase retardation of single CNC waveplates,we produce a 1/4 ? achromatic CNC-based waveplate consisting of three layers of aligned CNC films whose phase retardations and fast axis directions are calculated by Jones Matrix,with optimized achromatic properties.The fabricated achromatic waveplate is characterized by measuring the transmission spectra,and its maximum deviation of phase retardation is around 0.06 for the wavelength range of 460-660nm.The achromatic performance is improved by one order of magnitude compared with the single CNC waveplates.CNC waveplates are low-cost,flexible and can be tailored easily,showing potential applications in the polarization measurement,imaging and sensing fieldsThird,this thesis studies the self-assembly of silver nanowires in nematic CNC liquid crystals and their compound optoelectronic materials.Silver nanowires are doped into nematic CNC liquid crystals,whose orientation is parallel to the direction of CNCs uniformly.Silver nanowire-nematic CNC liquid crystals are aligned by shearing forces,and its orientations are determined by polarized optical and dark field microscopic images.The scalar order parpameter of aligned silver nanowire-CNC films is around 0.59,and exhibits the maximum ratio of anisotropic sheet resistance around 5 that is consistent with the simulated percolation probability using the Monte Carlo methodThis thesis shows the potential of cellulose liquid crystals in preparing low-cost,multifunctional,flexible optoelectronic nanomaterials and devices. |
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