含光學活性乳酸衍生液晶材料之液晶相與物理性質探討

Study on the Mesomorphic and Physical Properties of Chiral Liquid Crystals Containing Optically Active (L)-Lactate Group

林泓叡(Hung-Jui Lin)

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

從近來的文獻顯示,乳酸衍生誘電性液晶材料在光電特性具有傑出的表現,並具有以下三項特點: (i) 容易擁有寬廣溫度範圍的SmC*液晶相, (ii) 誘電性液晶相SmC*溫度接近室溫溫度, (iii) 具有高自發性極化值 (Ps )。
因此,我們設計了一系列以methyl (S)-(-)-lactate為起始物的新旋光性液晶材料,並研究其光電特性。

化合物I經1H-NMR 證實結構正確。並經由偏光顯微鏡與差式熱分析儀(DSC)測量相轉移溫度與熱焓值,再利用偏光顯微鏡的紋理圖來確定化合物I (m=9, 11)具有N*, SmA*及SmC*三液晶相,並且僅在降溫的過程中具有相轉移,相轉移的順序及相轉移溫度如以下所示:
I (m=9): Iso (138.88℃) N* (133.07 ℃) SmA* (106.17℃) SmC* (76.33℃)Cr1 (69.1℃) Cr2,
I(m=11):Iso(143.06℃)N*(137.35℃)SmA*(111.47℃)SmC*(74.29℃)Cr1.(54.82℃)Cr2
隨著鏈長‘m’的延伸, 化合物 I會具有較高的Iso-N*, N*-SmA*,SmA*-SmC*的轉換溫度, 但SmC*-Cr1的轉換溫度會較低及較高的熔點,因此我們發現化合物 I的SmC*液晶相熱穩定性會隨著‘m’的增加而增加。
化合物 I (m=9, 11)在光電性質的量測上,在Switching current量測結果顯示出Signal peak，因此證明其有誘電性SmC*相的存在。化合物I (m=9) Ps最大值可達32 nC/cm2，最大傾斜角θ=18°,化合物I (m=11) Ps最大值可達100 nC/cm2，最大傾斜角θ=19°。由此結果可知化合物 I隨著鏈長‘m’的延伸會造成Ps值和傾斜角θ的上升,而且當溫度低於Tc時, Ps值會隨著鏈長‘m’的延伸而變大。從結果顯示出非旋光末端的長度的確會對於SmC*液晶相的溫度範圍具有很明顯的影響。

關鍵字

層列A型液晶相 ； 誘電性液晶相 ； 膽固醇相

並列摘要

It is generally acknowledged that optically active lactic acid as chiral source for the preparation of chiral liquid crystals has outstanding mesomorphic and electro-optical propertiesm, such as (i) having wide temperature range of SmC* phase, (ii) the SmC* phase temperature is closed to the room temperature and (iii) having high spontaneous polarization (Ps value).
In this work, we designed and synthesized chiral liquid crystal materials, as shown bellow, by using (S)-(-)-lactate as the initial material, for the investigation of mesomorphic and electro-optical properties.

The phase sequences, transition temperatures and corresponding phase transition enthalpies of mesophase measured by DSC and optical microscope. The experimental result shows that compounds I (m=9, 11) are mesomorphic, and the mesomorphic phase sequences and transition temperatures are as follows:
I (m=9): Iso (138.88℃) N* (133.07 ℃) SmA* (106.17℃) SmC* (76.33℃)Cr1 (69.1℃) Cr2,
I(m=11):Iso (143.06℃) N* (137.35℃) SmA* (111.47℃) SmC* (74.29℃) Cr1.(54.82℃) Cr2
The results show that compounds I (m=9, 11) exhibit enantiotropic mesophases of the N*, SmA* and SmC* phases. An increasing nonchiral peripheral alkoxy chain lengths ‘m’ increased the Iso-N*, N*-SmA* and SmA*-SmC* transition temperatures but lower SmC*-Cr1 transition temperature. Temperature range of the SmC* phase increased with the increasing carbon chain length.
The results of electro-optic properties in these two materials have been demonstrated to exhibit ferroelectricity in SmC* phase by a single peak switching current of the switching behavior. The maximum spontaneous polarization (Ps value) of compounds I (m=9) in ferroelectric SmC* phase reaches 32 nC/cm2, and the maximum optical tilt angle reaches 18°. The maximum spontaneous polarization (Ps value) of compounds I (m=11) in ferroelectric SmC* phase reaches 100 nC/cm2, and the maximum optical tilt angle reaches 19°. The results show that increasing nonchiral peripheral alkoxy chain lengths ‘m’ increased spontaneous polarization (Ps value) and apparent tilt angle under the temperature of Tc .In conclusion, the results from above indicate that the nonchiral peripheral alkoxy chain length indeed have the significant effect on the stability of SmC* phase.

並列關鍵字

chiral smectic A phase ； ferroelectric C* phase. ； Cholesteric phase

參考文獻

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