The Effect of the Peripheral Chain Length and the Position of Second Chiral Center on the Formation of Thresholdless Antiferroelectric Phase

• Main Authors: Wang-Cheng Ya, 葉旺承
• Other Authors: jJiunn-Yih Lee
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/41969472199458392190

碩士 === 大同大學 === 化學工程研究所 === 88 === ABSTRACT The purpose of this research work was an attempt to elucidate the structure-property correlation in the chiral smectic liquid crystals, because the exciting results have been obtained this field of chiral system. A homologous series of chiral materials MApAmPBCNP(p=1-5,m=7-10) was designed for the synthesis and investigation of the structure-property relationship in the chiral liquid crystal system. The target compounds was modified independently by the length of the alkyl chain m and methylene group p for the study. Compounds MApAmPBCNP(p=1,m=7-10) mostly have the Iso-SA- SCγ*-Cr. transitions. In the compounds with non-chiral peripheral chain length m=11~ 12, a TGBA phase mediated between isotropic liquid and SA phase with the temperature range of 0.1~0.2℃were detected. The study of dielectric property, switching behavior and electro-optical response demonstrates that these chiral materials in the ferrielectric SCγ* phase possesses thresholdless antiferroelectricity. The variations of peripheral chain length, m, in the SCγ* phase in this series of compounds MApAmPBCNP(p=1,m=7-10) have no remarkable effect on the spontaneous polarization, dielectric property and switching behavior. The moderate peripheral chain length of MApAmPBCNP(p=1,m=7-10) favors the formation of good V-shaped switching behavior in the SCγ* phase. Compounds MApAmPBCNP(p=1-5,m=10) have the Iso-SA-SCγ*-Cr. transitions. The study of dielectric property, switching behavior and electro-optical response demonstrates that these chiral materials in the ferrielectric SCγ* phase possesses thresholdless antiferroelectricity. The variations of methylene chain length -(CH2)p-, p in the series of compounds MApAmPBCNP(p=1-5, m=10), also have no remarkable effect on dielectric property and switching behavior in the SCγ* phase. The spontaneous polarization values are lightly decreased as increasing the methylene chain length, this series of compounds MApAmPBCNP(p=1-5,m=10) favors the formation of good V-shaped switching behavior in the SCγ* phase. Investigating the effect of temperature, frequency and cell thickness on the electro-optical response in SCγ* phase demonstrates that the V-shaped switching property in SCγ* phase is strongly depended on the temperature, frequency of the applied voltage and the thickness of homogeneous cells. In conclusion, the results from above indicate that of MApAmPBCNP (p=1,m=7-10) and MApAmPBCNP(p=1-5,m=10) possess ferrielectric phase, SCγ* phase. Good V-shaped switching behavior achieved in the SCγ* phase. It also indicates the variations of peripheral chain length, m and methylene chain length -(CH2)p-, p favors the formation of good V-shaped switching in the SCγ* phase. The V-shaped switching behavior is critically depended on the temperature, frequency of the applied voltage and the thickness of homogeneous cells.