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URN etd-0626106-162319 Statistics This thesis had been viewed 2041 times. Download 797 times. Author Ming-Che Li Author's Email Address No Public. Department Chemical Engineering Year 2005 Semester 2 Degree Master Type of Document Master's Thesis Language English Page Count 111 Title Ferroelectric and Antiferroelectric Properties of Novel Chiral Liquid Crystals Derived from (S)-1-methyl-2-[(2'-methoxy)ethoxy]ethanol Keyword V-shaped switching ferroelectrics antiferroelectrics antiferroelectrics ferroelectrics V-shaped switching Abstract 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 optically active (S)-1-methyl-2-[(2’-methoxy) ethoxy]ethanol 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 achiral peripheral methylene chain length ‘m’ and (ii) the lateral fluoro substituents in the phenyl ring of the core.
The results showed that compounds I(m=8-12) exhibited the phases sequence of SmA*-SmC*-SmX*, compounds II(m=8-12) exhibited the phases sequence of SmA*-SmC*, while the compound II(m=9) posesses an additional SmX*. In the compounds III(m=8-12), compounds III (m=8, 9) with shorter alkyl chain displayed an enantiotropic phase sequence of SmA*-SmCA* while compounds III(m=10-12) with longer alkyl chain exhibited enantiotropic phase sequence of SmA*-SmC*. Extending achiral alkyl chain length in compounds I(m=8-12) and III(m=8-12) stabilizes the temperature ranges of SmC* phase, but suppresses the formation of SmA* phase. In compounds II(m=8-12), as the achiral alkyl chains are extended, the transition temperatures of SmC*-Cr are increased but the temperatures ranges of SmC* phase are decreased.
The compounds with lateral fluoro substituents in the phenyl ring of core could affect the formation of the mesophase, lower the transition temperatures, melting points and clearing points. Moreover, the phenyl ring with 2-fluoro substituent possesses higher transition temperature than that with 3-fluoro substituent, suggesting that molecular broadening minimized due to the sterically shielded of 2-flueoro substituent.
The electro-optical responses of chiral compound II(m=11) in the SmC* phase displayed V-shaped switching behavior, chiral compound III(m=9) in the SmCA* phase displayed U-shaped and double hysteresis loop switching behavior. Comparison of compounds I,II, III(m=8~12) clearly show that the compounds I(m=8-12) have higher Ps values than the compounds II, III(m=8-12), suggesting that compounds with the lateral fluoro substituents could suppress the polarity of the transverse dipole. The maximum Ps values of I, II, III(m=9-12) are about 6-16 nC/cm2. The compounds III(m=8-12) with 3-fluoro substituent have higher tilt angle than the compounds I, II(m=8-12). The maximum optical tilt angle values of the compounds I, II, III (m=8-12) were between 20-30o.
Advisor Committee Shune-long Wu - advisor
Chain-Shu Hsu - co-chair
Chin-Tsou Kuo - co-chair
Hong-Cheu Lin - co-chair
Files Date of Defense 2006-06-16 Date of Submission 2006-06-26