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URN etd-0723104-102429 Statistics This thesis had been viewed 2013 times. Download 313 times. Author Tzu-Chin Lin Author's Email Address email@example.com Department Chemical Engineering Year 2003 Semester 2 Degree Master Type of Document Master's Thesis Language English Page Count 153 Title SYNTHESIS AND PROPERTIES OF NOVEL CHIRAL LIQUID CRYSTALS DERIVED FROM (S)-2-(6-METHOXY-2-NAPHTHYL)PROPIONIC ACID Keyword liquid crystals ferroelectric liquid crystals ferroelectric liquid crystals liquid crystals Abstract The aim of the research work was intended to study the effect of terminal chiral chain moiety on the mesophases and mesomorphic properties. By means of chiral compound, (S)-2-(6-methoxy-2-naphthyl)propionic acid as building block, seven homologous series of liquid crystal materials comprised of different chiral chain were synthesized for investigating the correlation between the chemical structure of chiral tails and mesomorphic properties.
Chiral swallow-tailed compounds (S)-2-(6-(4-(4¢-alkanoyloxyphenyl))benzoyl-
oxy)-2-napthyl)propionate, PmPBNP (m=7-11) and 2-ethyl-1-butyl (S)-2-(6-(4-(4¢-
alkanoyloxyphenyl)benzoyloxy)2-napthyl)propionate, EBmPBNP (m=7-11) were synthesized for studying the effect of swallow-tailed moiety of chiral chain on mesomorphic properties.
Compounds PmPBNP (m=7-8), display enantiotropic mesophases of the N*, TGBA*, SmA* and CrX* phases whereas the materials PmPBNP (m=9-11) show enantiotropic mesophases of the N*, TGBA*, SmA* and SmCA* phases. An increasing chain length of methylene (m) can enhance the thermal stability of the SmCA* phase, but the temperature range of the SmA* phase decreases. The study of switching curve, miscibility study and dielectric property demonstrates that the series of chiral materials possess SmCA* phase. The magnitude of spontaneous polarization for materials PmPBNP(m=9-11) increase as the length of achiral aliphatic chain increases. The thresholdless, V-shaped switching property can be obtained in the SmCA* phase.
Compounds EBmPBNP (m=8-11) show the enantiotropic mesophases of the N*, SmA*, SmC* and CrX* phases whereas compound EB7PBNP shows enantiotropic mesophases of the N*, SmA*, and CrX* phases. As the chain length of terminal achiral chains increasing, the temperature range of the SmC* phase becomes wide while that of the SmA* phase becomes narrow. Moreover, extending of a methylene between chiral center and swallow-tailed moieties leads to suppress the thermal stability of mesophases. The magnitude of spontaneous polarization for materials EBmPBNP (m=8-11) increase as the length of achiral aliphatic chain increases. The study of electro-optical response indicates that this series of chiral materials in the SmC* phase exhibit thresholdless, V-shaped switching property.
Four homologous series of chiral semi-fluorinated liquid crystals, PBNP(p,m,n) (p=7-11; m=3, n=2; m=2, n=4; m=3, n=4; m=2, n=6), were synthesized for investigating the influence of semi-fluorinated chain on mesomorphic properties. In addition, a homologous series of non-fluorinated compounds, PBNP(p,6,0), were synthesized in order to compare to the fluorinated compounds, PBNP(p,2,4).
Compounds PBNP(p,m,n) (p=7-11; m=3, n=2; m=2, n=4; m=3, n=4; m=2, n=6) mostly show the enantiotropic mesophases of SmA* and SmC* phases. The results reveal that introduction of semi-fluorinated chain on chiral tails indeed favor the formation of the smectic phases and enhance the thermal stability of the mesophases. The study of texture observation, switching current behavior and dielectric properties demonstrates that these chiral materials truly possess existence of the SmC* phase. The results of the electro-optical response exhibit the thresholdless, V-shaped switching property in the SmC* phase. Furthermore, both non-fluorinated and fluorinated compounds, for example of PBNP(p,6,0) and PBNP(p,2,4), the V-shaped switching can be obtained in the SmC* phase at appropriate frequency and temperature.
In conclusion, the results indicate that these chiral materials derived from (S)-2-(6-methoxy-2-naphthyl)propionic acid seem favorable for the formation of the thresholdless and V-shaped switching properties.
Advisor Committee Shune-Long Wu - advisor
Hong-Cheu Lin - co-chair
Jin-Jei Wu - co-chair
Files Date of Defense 2004-06-10 Date of Submission 2004-07-23