探討氟化程度對誘電與反誘電性液晶相 及其性質的影響

Effect of Fluorinated Extent on the Mesophases and Mesomorphic Properties of Ferroelectricity and Antiferroelectricity Phases of Liquid Crystals

李怡芳(Yi-Fang Li)

指導教授 ： 吳勛隆

大同大學/工程學院/化學工程學系所/碩士(2007年)

摘要

本研究的主要目的為探討旋光部分的氟化程度於旋光性液晶材料中，對於生成誘電性液晶相及反誘電性液晶相的影響。合成五系列同樣以(S)-propylene oxide為起始物並與半氟化醇類反應之旋光性液晶材料，以探討氟化程度與非旋光末端烷鏈”m”的長度對於液晶相及物理光電特性的影響。
藉由偏光紋理圖及DSC的鑑定可分別得知液晶相及相轉移溫度的變化，經由電流轉換行為及介電性質的量測可進一步鑑定誘電性及反誘電性液晶相的存在。
實驗結果指出:具有半氟化液晶材料I(m=8-12)，III(m=7-12)及IV(m=8-12)有利於反誘電性液晶相的生成﹔半氟化烷鏈末端原子以氫取代的液晶材料II(m=8-12)及具有未氟化液晶材料V(m=8-12)則傾向生成誘電性液晶相。旋光末端之半氟化烷鏈的長度由-CF3(化合物I(m=8-12)),-CF2CF3(化合物III(m=7-12)) 增加至-CF2CF2CF3 (化合物 IV(m=8-12))，結果顯示液晶相熱穩定度會隨之增加，尤其是對反誘電性液晶相的熱穩定度而言。
在物理性質量測方面結果顯示:自發性極化值與氟化程度並無明顯的關係。但傾斜角會隨氟化程度的增加而有明顯增加。且旋光性液晶材料IV(m=10)於反誘電性液晶相下量測產生V型光電轉換行為。

關鍵字

半氟化旋光性液晶材料、誘電性液晶、反誘電性液晶、V型轉換行為

並列摘要

The purpose of this research work was an attempt to elucidate how the extent of fluorination at chiral group of chiral liquid crystal materials affects the formation of ferroelectric and antiferroelectric phases. Five series of chiral liquid crystal materials derived from (S)-propylene oxide reacting with semi-fluorinated alkanols under base condition, were designed and synthesized. The target compounds were independently modified by the extent of fluorination and the length of the achiral alkyl chain “m” for study.
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 compounds I(m=8-12), III(m=7-12) and IV(m=8-12) facilitate the formation of antiferroelectric phase; while compounds II(m=8-12) containing one hydrogen atom at the end of semi-fluorinated chiral alkane and compounds V(m=8-12) with non-fluorinated alkane at chiral group enhance the tendency to form a ferroelectric phase. The extension of semi-fluorinated chiral alkyl length from -CF3 (compounds I(m=8-12)), -CF2CF3 (compounds III(m=7-12)) to -CF2CF2CF3 (compounds IV(m=8-12)) results in an enhancement of the thermal stability of mesophases, especially, the SmCA* phase.
The physical properties of the chiral materials in ferroelectric SmC* and antiferroelectric SmCA* phases were also measured. The results obtained from the measured maximum Ps values for the materials in the SmC* or SmCA* phase show no significant correlation to the extent of the fluorination on the chiral group of the compounds. However, the results from the measured maximum apparent tilt angles for the materials in the SmC* or SmCA* phase sow that the extent of fluorination at the chiral tail of the compounds increases, the optical tilt angle (θ) increases. It was interesting to find that the electro-optical response of the chiral material IV(m=10) in the antiferroelectric SmCA* phase display V-shaped switching behavior at appropriate frequency and temperature.

並列關鍵字

antiferroelectricity ； ferroelectricity ； semi-fluorinated chiral liquid crystal ； V-shaped switching behavior

參考文獻

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