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URN etd-0723108-145744 Statistics This thesis had been viewed 2610 times. Download 1108 times. Author Bing-hung Sie Author's Email Address No Public. Department Chemical Engineering Year 2007 Semester 2 Degree Master Type of Document Master's Thesis Language English Page Count 123 Title Study on the Effect of Semi-fluorinated Alkyl Chain Length on the Mesomopic Phase of Chiral Liquid Crystals containing Naphthalene Core Keyword ferroelectricity antiferroelectricity semi-fluorinated chiral liquid crystal semi-fluorinated chiral liquid crystal antiferroelectricity ferroelectricity Abstract Optically active alcohols, (S)-1-(2,2,2-trifluoroethoxy)-2-butanol, (S)-1-(2,2,3,3,3-pentafluoropropoxy)-2-butanol and (S)-1-(2,2,3,3,4,4,4-heptafluorobutoxy)-2-butanol, were designed and synthesized by the treatment of (S)-butylene oxide with fluorinated alchols under basic condition. Five novel homologous series of chiral fluorinated materials derived from these alcohols, (R)-1-(2,2,2-trifluoroethoxy)-2-butanol, (R)-1-(2,2,3,3,3-pentafluoropropoxy)-2-butanol, and (R)-1-(2,2,3,3,4,4,4-heptafluorobutoxy)-2-butanol, were than synthesized for the investigation concerning the effect of the extent of fluorination at the chiral group of the molecule on the formation of SmC* and SmCA* phases. The results obtained from the study of five series of chiral materials, I(m=8-12, n=1, q=1), Ⅱ (m=8-12, n=1, q=3), III(m=8-12, n=2, q=1), IV(m=8-12, n=2, q=2) and V(m=8-12, n=2, q=3) can be summarized as follows:
The mesomorphic phases and their corresponding transition temperatures were primarily characterized by the microscopic textures and DSC thermograms, and the ferroelectric and antiferroelectric phases were further identified by the measurements of electric switching behavior and dielectric constant ε'.
Comparing semi-fluorinated liquid crystal materials possessing ethyl substituent to that possessing methyl substituen at the aymetric carbont, the former suppress the formation of antiferroelectric phase. Compounds III(m=8-12, n=2, q=1), IV(m=8-12, n=2, q=2 and V(m=8-12, n=2, q=3) possess enantiotropic SmA* and SmCA* phases.The extension of semi-fluorinated chiral alkanes increase from -CF3, -CF2CF3 to -CF2CF2CF3 resulted in an enhancement of the stability of mesophases, especially, the SmCA* phase. Extending phenyl ring to biphenyl ring in the core of the molecules could result in increasing melting point, clear point and thermal stability of mesophases, and changing the formation of antiferroelectric SmCA* phase from monotropic to enantiontropic mesophase.
The physical properties of the chiral materials in ferroelectric SmC* and antiferroelectric SmCA* phases were also measured. The magnitudes of maximum Ps values are decreased with the extension of the lateral group at the asymmetric carbon atom from methyl to ethyl group, as compared to the corresponding structural similar chiral materials. The magnitudes of maximum Ps values are increased with the extension of chiral fluorinated alkyl chains from –CF3, -CF2CF3 to CF2CF2CF3. The magnitudes of apparent tilt angle (θ) values show that there is no significant correlation to the extension of fluorinated alkyl chain lengths, lateral alkyl substituent from methyl to ethyl group and addition ring at core structure.
Advisor Committee Shune-Long Wu - advisor
Chin-Tsou Kuo - co-chair
Jin-Jei Wu - co-chair
Wen-Fu Lee - co-chair
Files Date of Defense 2008-06-25 Date of Submission 2008-08-01