| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 87 === The use of polymer networks to stabilize and modify liquid crystal phases for display-based applications has recently become widespread. Polymer stabilized cholesteric textures (PSCTs) represent one such class of whose applicability extends to both reflective and transmissive displays.
Chiral (+)-bornyl methacrylate [(+)-BMA], (+)-bonrnyl acrylate [(+)-BA], (+)-isobornyl acrylate [(+)-IBA], achiral (±)-BMA, (±)-IBA were synthesized from (+)-camphor and (±)-camphor, respectively. Achiral monomer of 4-4''Bis[6-(acryloyloxy)hexyloxy]biphenyl (BAHB) was synthesized from 4,4-hydroxybiphenyl. To investigate the dependence of chiral and achiral polymers on optoelectronic characteristics of PSCT cells, a mixture of commercial available positive nematic liquid crystal E48 and cholesteric liquid crystal CB15 was dispersed in chiral and achiral polymer matrixes. The optoelectronic characteristics and microstructures of the PSCT cells with various monomers were investigated.
From the results of the experiments, it was found that the reactivity of monomers and microstructures of polymer matrixes obtained in PEG400 were different from those obtained in cholesteric liquid crystal. Polymer matrixes formed from monofunctional monomers of (+)-BMA, (±)-BMA, (+)-BA, (+)-IBA and (±)-IBA were found no ability to stabilize liquid crystal due to their low reacitivity in cholesteric liquid crystal. For BMA system, however, the polymer matrix could stabilize liquid crystal when the polymer was polymerized in the presence of low initiator concentration. Effects of polymer matrix on PSCT cells increased with increasing the BMA concentration lead to the increasing of driving voltage, hysteresis and contrast. Reactivity of copolymerization of EGDMA with various chiral monomers decreased with increasing the chiral monomer concentration. Formation of sparse polymer matrix lead to the decreasing of driving voltage, hysteresis and contrast. In theory, enantiomers have different reactivity in the chiral environment. Copolymerization of EGDMA with chiral and racemic monomers will give different microstructures of polymer matrix and with various effects on the optoelectronic characteristics of PSCT cells. The response time is affected by the viscosity and the pitch of cholesteric liquid crystal. UV light strength also affected the reactivity of polymerization and microstructures of polymer matrix. While using a low strength UV irradiation, a large sponge like and ordered polymer matrix was formed and lead to the decreasing of driving voltage and increasing of hysteresis. The optimal feed monomer ratio of EGDMA/(+)-BMA= 1:1, showed excellent optoelectronic characteristics, was observed in this investigation.
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