Syntheses and Mesomorphic Behaviors of Antiferroelectric Liquid Crystals Consisted of Mono- and Di-Styryl Benzene Derivatives
| Autor: | Fang-Cheng Yu, 俞方正 |
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| Rok vydání: | 2002 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 90 This study empolyed stilbene as a core to construct rod-like chiral mesogens and banana shaped mesogens.The mesophase behaviors were studied by optical polarizing microscopy and differential scanning calorimetry.The rod-like chiral mesogens were obtained by esterification of 4-alkoxy—3—fluoro -(4’-hydroxy)stilbene with mono ester of terephthalic acid having (1) S-2-methylbutanol, and (2) L—ethyl lactate as the chiral moieties, CnFSTMBT and CnFSTLET, respectively.(1)CnFSTMBT, where n = 6, 7, 8, 9, 10, 12, exhibited enantiotropic I-BP-N*- TGBA-SA-Sc*-K phase sequence with temperature range of 130℃. As compared to those of the non-fluoro homologues, the clearing point and melting point are slightly lower and the mesophase temperature range is slightly narrower. However, the frustrated (BP and TGBA) persisted although with narrower ranges.(2)CnFSTLET, where n = 6, 7, 8, 9, 12, exhibited enantiotropic I-N*-TGB- SCA*-K phase sequence with temperature range of 110℃. Compare to the CnFSTMBT homologues, the disappearance of Blue Phase and appearance of SCA* are attributed to the dipole moment and twisting power of the lactate moiety. The TGB phase occurs between the N* and SCA* is tentatively assigned to be TGBc on the basis of microscopic observation. Further study is necessary to identify this phase.The banana shaped mesogens were obtained with three different bent cerntral cores.(1)3,4’-bis((4-alkoxybenzoyloxy)-benzoyloxy)stilbene (3-4’-(CnOBB)2ST, where n = 8, 10, 12, 14, 16)exhibited enantiotropic banana phases, B1 phase for n = 8, 10, and B2 phase for n = 12, 14, and 16. The mesophases temperature ranges are about 100℃, much wider than those reported in the literature.(2)1,3-bis(2-(4-alkoxybenzoyloxyphenyl)ethenyl)benzene(1,3-(CnOBST)2B, where n = 8, 10, 12, 14, 16), monotropic B2 phase for n = 12, and enantiotrpic B2 phase for n = 14, 16. The rather short mesophase temperature ranges is attributed to the coplanarity of distyrenyl benzene, which would result in a stronger π-π stacking. (3)1,3-bis(2-(4-(4-alkoxybenzoyloxy)phenoxycarbonyl)ethenyl)benzene(1,3-(CnOBBAc)2B, where n = 12,16)exihibited peculiar enantiotropic smectic phases, banana leaf-like texture for n = 12, fractal and focal conic for n = 16. These phases require further studies for characterization. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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