Synthesis and Properties of New Chiral Swallow-tailed Liquid Crystals

• Main Authors: Fu-Chieh Lu, 盧甫杰
• Other Authors: Shune-Long Wu
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/22155411874234723356

碩士 === 大同大學 === 化學工程研究所 === 89 === The primary of this research work was an attempt to elucidate the structure-property correlation in the chiral smectic liquid crystals. A homologous series of chiral swallow-tailed materials, (S)HNP(p,n,q), was designed for the synthesis and investigation of the structure-property relationship in the chiral liquid crystal system. The target compounds were modified independently by the length of the alkyl chain (p), methylene group (n) and swallow-tailed group (q) for the study. Compounds (S)HNP(p,0,3; p=10~12) display enantiotropic mesophase of the N*, TGBA* and SA phase. The variations of alkyl chain length (p) shows that the TGBA* phase is stabilized as the number of alkyl chain length increase, but the N* and TGBA* phase have no significant changed. Compounds (S)HNP(p,1,3; p=9~14) display enantiotropic mesophase of the SA and SCA* phase. The variation of alkyl chain length (p) show that the temperatures of the clear point and the SA phase is slightly suppressed as the alkyl chain is increased from 9 to 14. The stability of the SCA* phase increase from compound p=9 to p=13 and then decrease at p=14. The study of electro-optical response demonstrates that this series of chiral material in the antiferroelectric phase (SCA*) possess thresholdless, V-shaped switching property. The variations of alkyl chain length (p) in this series of chiral material (S)HNP(p,1,3) have no remarkable effect on spontaneous polarization, dielectric property and switching behavior in the SCA* phase. The results obtained from compounds (S)HNP(10,n,q; n=0,1; q=2,3) display that with the exception of the (S)HNP(10,0,3), the rest members in the series of (S)HNP(10,n,q) exhibited the SCA* phase. In addition, when increasing the linking group(n) from 0 to 1, the higher disordered liquid crystalline phases are disappeared and the higher order liquid crystalline phase i.e. the SA and SCA* phases remained. The variation of the methylene group (n) and swallow-tailed group (q) in this series of chiral material (S)HNP(10,n,q) have no remarkable effect on spontaneous polarization, dielectric property and switching behavior in the SCA* phase. The V-shaped switching obtained from the chiral materials is shown to critically depend on the temperatures of the SCA* phase and frequencies of applied voltage. In conclusion, the results indicated that the chiral swallow-tailed materials derived from (S)-2-(6-Methoxy-2-napthy)propionic acid are favorable for the formation of the antiferroelectric phase. Moreover, the antiferroelectric phase of the materials in homogeneous aligned cells possess thresholdless V-shaped switching property. An addition a methylene group between the carboxyl group and swallow-tailed group increasing the thermal stability of the smatic phase. The V-shaped switching is critically depended on the temperatures of the SCA* phase, frequencies of applied voltage and structure of the compounds.