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Title page for etd-0806109-142356


URN etd-0806109-142356 Statistics This thesis had been viewed 2345 times. Download 1100 times.
Author Zong-Yu He
Author's Email Address No Public.
Department Chemical Engineering
Year 2008 Semester 2
Degree Master Type of Document Master's Thesis
Language English Page Count 116
Title Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing
Lateral Methoxymethyl Substituent
at Chiral Center
Keyword
  • title angle
  • electro-optical property
  • ferroelectric phase
  • Chiral materials
  • Chiral materials
  • ferroelectric phase
  • electro-optical property
  • title angle
  • Abstract The major research work of this study is an attempt to correlate the structure-property relationship of chiral liquid crystals in terms of variation of achiral and chiral alkyl chains in the chiral liquid crystal materials possessing methoxymethyl group attached to the chiral centre. Thus, the optically active alcohols, 1-methoxy-2-pentanol, 1-methoxy-2-heptanol, 1-methoxy-2-octanol and 1-methoxy-2-nonanol, for the use as the building blocks of the chiral liquid crystals were designed and synthesized by the Grignard reaction of (R)-glycidyl methyl ether with alkyl magnesium chlorides. In consequence, four novel homologous series of chiral materials, (S)-1-methoxy-2-pentyl 4-{4’-[(4”-alkoxyphenyl)phenylcarbonyloxy]}benzoate, I-6 (m=8-12, n=2), (S)-1-methoxy-2-heptyl 4-{4’-[(4”-alkoxyphenyl)phenylcarbonyloxy]}benzoate, II-6 (m=8-12, n=4), (S)-1-methoxy-2-octyl 4-{4’-[(4”-alkoxyphenyl)phenylcarbonyloxy]}benzoate, III-6 (m=8-12, n=5) and (S)-1-methoxy-2-nonyl 4-{4’-[(4”-alkoxyphenyl)phenylcarbonyloxy]}benzoate, IV-6 (m=8-12, n=6) derived from these alcohols were synthesized for the investigation of the mesophases and electro-optical properties. In addition, the differences in mesomorphic phases and electro-optical properties of the chiral materials with methoxymethyl group (-C*HCH2OCH3) and propyl group (-C*HCH2CH2CH3) were compared.
    The mesomorphic phases and their corresponding transition temperatures were primarily characterized by the microscopic textures and DSC thermograms, and the ferroelectric phases were further identified by the measurements of electric switching behavior and dielectric constant ε'.
    The results show that, all compounds display enantiotropic mesophases of the SmA* and SmC* phases. The compound II-6 (m=8, n=4) exhibit an additional SmCγ* phase. An increasing aliphatic alkyl chain lengths (m) decreases the clearing point, the thermal stability of the SmA* phase and transition temperature of SmA* phase to SmC* phase. In addition, the extension of terminal chiral alkyl chain lengths (n) in all series of compounds results in the decreasing cleaning point and transition temperature of SmA* phase to SmC* phase.
    A comparison of structurally similar chiral materials possessing methoxymethyl substituent to that possessing propyl substituent at the asymmetric carbon of the chiral group, show that the formers have lower melting point, facilitate the formation of the SmC* phase and suppress the formation of the SmCA* phase.
    The physical properties of the chiral materials in ferroelectric SmC* phases were measured. The maximum magnitudes of spontaneous polarization measured for the materials in the SmC* phase are in the range of 32 to 115 (nC/cm2). These results indicate that the maximum Ps values reveal no significant correlation to the change of achiral alkyl chains, m. However, the Ps values are increased by the extending of chiral alkyl chains, n. The results are due to, as the chiral alkyl chain is extended, the chiral center and a certain portion of the alkyl chain are supposed to spend more time lying along the long axis of the molecule, such that the chiral center has a fixed spatial arrangement with respect to its local environment, this in tern will fix the orient of the diple at the chiral center.
    The maximum apparent title angles (θ) measured for materials in the SmC* phase are in the range of 20° to 40°. These results of maximum apparent title angle (θ) reveal no significant correlation to the change of achiral and chiral alkyl chains (m and n).
       In conclusion, the chiral materials possessing lateral methoxymethyl substituent attached at chiral center were successfully synthesized, and the structure-property correlation in terms of achiral and chiral alkyl chain lengths for the formation of ferroelectric liquid crystals was established. The establishment of this correction will be beneficial for the future design and synthesis of more ferroelectric liquid crystals.
    Advisor Committee
  • Shune-Long Wu - advisor
  • Jin-Jei Wu - co-chair
  • Liang-Jye Yu - co-chair
  • Files indicate access worldwide
    Date of Defense 2009-07-09 Date of Submission 2009-08-06


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