| Summary: | 碩士 === 淡江大學 === 化學學系碩士班 === 94 === Synthesis and Properties of 3- and 4- Hydroxy Benzoic Acids Derivatives : Unsymmetrical Liquid Crystals
Total Page:93
Name of Institute: Graduate School of Chemistry Tamkang University
Graduate Date: July, 2006 Degree Conferred: Master
Name of Student: Che-Cheng Chang Advisor: Dr. Liang- Jye Yu
Abstract:
It can divide into 2 parts in this research. One is bent-shape liquid crystals, which are derivatives from 3-Hydroxy Benzoic Acid. Another is chiral rod-like liquid crystals which are derivatives from 4-Hydroxy Benzoic Acid. The mesophase behaviors were studied by optical polarizing microscopy, differential scanning calorimetry and powder X-ray diffraction.
In the first part, according to different method, there are 4 to 6 benzene rings compounds and different alkoxy terminal chains to be synthesis. In 4B and 5B series, we can not observe liquid crystal phase, but in literature there are liquid crystal phase in the symmetry 5 rings system. Herein, we inference the absence of the liquid crystal phase is due to unsymmetrical structure of 5B series. In Bn-5BC12, we can observe N and SmC phase; In the 6 benzene rings system (6B series), there are series of liquid crystal phases. Consequently, we consider that in the 5 rings system need more symmetrical structure to receive liquid crystal phase; In the unsymmetrical system, because of its unusual structures, they need stronger π-π interaction to receive liquid crystal phase (5BC12), and more stronger π-π interaction to receive banana liquid crystal phase.
The second part, we synthesis the chiral rod- like liquid crystals with lactate derivatives (m-n series). The core consists of 4 benzene rings, two wings substitutes by alkoxy chains and lactate derivatives. In all series of this part, exhibited I-N*-SmC*(-SmX*)-K phase sequence. The most noticeable place, lies in its “helix inversion”. As the n value (alkoxy chain) increase, the mesophase prefer to form smectic phase (SmC*, SmX*). Temperature of the helix inversion is occurred, called “inversion point ”. The inversion point depended on lactate-side alkoxy chain length. Methyl lactate derivative series, the inversion point is about 140℃; Ethyl lactate derivative series, the inversion point is about 180℃; but butyl lactate derivative series cannot observe helix inversion, we inference it occurs in 240℃, but at this temperature the compound already become isotropic. In opposite, the length of the alkoxy chain has no influence on inversion point.
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