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URN etd-0723108-145608 Statistics This thesis had been viewed 2191 times. Download 688 times. Author Shih-Ho Hsiao 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 125 Title Study on the Mesophases and Eletric-optical Properties of Chiral Materials possessing Lateral Ethyl Substituent and Various Fluorinated Alkyl Chains at Chiral Tail Keyword antiferroelectric phase. semi-fluorinated liquid crystal materials ferroelectric phase ferroelectric phase semi-fluorinated liquid crystal materials antiferroelectric phase. Abstract ABSTRACT
The purpose of this research work was an attempt to elucidate the effect of the extension of semi-fluorinated chiral alkyl length of liquid crystal materials possessing the lateral ethyl substituent at asymmetric carbon on the mesomorphic and electro-optical properties. Four series of chiral liquid crystal materials derived optically active chiral alcohols which were previously prepared from (S)-butylene oxide reacting with semi-fluorinated and non-fluorinated alkanols under basic condition, were designed and synthesized to investigate the mesomorphic and electro-optical properties.
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'.
The results show that the semi-fluorinated liquid crystal materials can enhance the thermal stability and the temperature range of antiferroelectric phase by extending the length of semi-fluorinated chiral alkyl chains at chiral tail from -CF3 (compounds II-6(m=8-12)), -CF2CF3 (compounds III-6(m=8-12)) to -CF2CF2CF3 (compounds IV-6(m=8-12)). Comparing the non-fluorinated with semi-fluorinated liquid crystal materials, the results show that the semi-fluorinated materials facilitate the formation of antiferroelectric phase but the ferroelectric phase becomes eclipsed. Comparing the liquid crystal materials possessing the lateral ethyl to that possessing methyl substituent at the asymmetric carbon, the former facilitate the formation of antiferroelectric phase but suppress the formation of ferroelectric phase.
The physical properties of the chiral materials in ferroelectric and antiferroelectric phases were also measured. In the semi-fluorinated liquid crystal materials, the maximum Ps values are increased but the optical tilt angles (θ) have no obvious differences by extending the length of semi-fluorinated alkyl chains at chiral tail from -CF3 (compounds II-6(m=8-12)), -CF2CF3 (compounds III-6(m=8-12)) to -CF2CF2CF3 (compounds IV-6(m=8-12)). Comparing the non-fluorinated with semi-fluorinated liquid crystal materials, the latter have the higher maximum Ps values and the optical tilt angles (θ) then the former. Regardless of semi-fluorinated or non-fluorinated liquid crystal materials, the results show that the maximum Ps values decrease but the optical tilt angles (θ) increase by extending the lateral alkyl substituent at the asymmetric carbon from methyl to ethyl groups.
In conclusion, the chiral materials having fluorinated alkyl chain and lateral ethyl substituent at asymmetric carbon of the chiral group facilitate the formation of antiferroelectric phase, eclipse the ferroelectric phase, decrease the meting point and the maximum Ps value, but increase the optical tilt angle (θ), as compared to the structural similar chiral materials having lateral methyl substituent at the asymmetric carbon.
Keywords: semi-fluorinated liquid crystal materials, ferroelectric phase, antiferroelectric phase.
Advisor Committee Shune-Long Wu - advisor
Chain-Shu Hsu - co-chair
Hong-Cheu Lin - co-chair
Yih-Hsing Lo - co-chair
Files Date of Defense 2008-06-23 Date of Submission 2008-08-01