| Summary: | 碩士 === 大同大學 === 化學工程學系(所) === 93 === The primary of this research work was an attempt to elucidate the correlation between structure and property in the chiral smectic liquid crystal. A homologous series of chiral materials derived from (S)-lactic acid has been successfully synthesized and the structures-property relationship investigated in the chiral liquid crystal system. The target compounds were modified independently by (i) the nonchiral peripheral methylene chain length ‘m’ and (ii) the lateral substitution group in the core.
Chiral materials of two series I(m=8~12) and II(m=8~12) displayed enantiotropic mesophases of the SmA* and SmC* phases. The shorter chain members III(m=8, 9) of the third series III(m=8~12) displayed an enantiotropic phase sequence of SmA* and SmC* phases while the longer chain members III(m=10~12) exhibited enantiotropic phase sequence of N*, TGBA*, SmA* and SmC* phases. With the increasing nonchiral methylene chain lengths ‘m’, the temperature range of the mesophase decreases, and the clearing point decreases and the crystal point increases. The materials with lateral 2-fluoro substitution in the phenyl ring of core could depress the formation of mesophase, lowering the transition temperature, melting point, clearing point and Ps values.
The electro-optical response in the series of chiral materials in the SmC* phase displayed typical ferroelectric hysteresis loop or hysteresis-free, V-shaped switching property upon various applied frequencies and temperatures. The maximum Ps values of I(m=9~11), II(m=9~11) and III(m=9~11) vary form 62.92~85.92 nC/cm2 and the maximum optical tilt angle values of the compounds I, II, III(m=9~11) were between 24o~32o.
In conclusion, the results indicated that the chiral alklysulfanyl chain materials derived from (S)-lactic acid with the lateral 2-fluoro substitution in the phenyl ring of core was favorable for the formation of the wide temperature range of the ferroelectric phase. V-shaped switching behaviors appear in the SmC* phase of the chiral materials of the series I(m=9) and II(m=8, 9).
|
|---|
