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  • 學位論文

新型超分子液晶膠之製作與應用

The Fabrication and Application of Novel Supramolecular Liquid Crystal Gels

指導教授 : 趙治宇

摘要


本論文旨在探討新型超分子液晶膠之製作與對於光電元件上的應用。液晶膠是一種被廣泛應用在光電領域的材料,如高導電度的液晶半導體、可重複切換讀寫的雙穩態記憶體、或是可快速反應的扭旋向列型液晶元件。在這個研究中,我們使用了一種新型的芴系共聚物(polyfluorene-based polymer) 作為此超分子液晶膠的凝膠因子。此凝膠因子與絲狀液晶混合後,可藉由其本身所具有的長鏈共軛π電子結構進行自我組裝,而形成網絡狀的超分子結構。在實驗中,我們先將向列型液晶材料與此具有共軛π電子結構之凝膠因子材料混和以製備液晶膠。作法是將此混和物加熱至使液晶呈現均向性(isotropic)之相位,在此狀態下將混和液注入準備好的液晶晶胞元件中(內部鍍有ITO導電電極及配向層),再使之緩慢的降溫。當溫度降至液晶的向列型相位(nematic)溫度後,由於配向層的使用,凝膠因子會因為液晶的基板效應而被排列。當溫度進一步下降至凝膠因子的膠化溫度時,凝膠因子會因分子之間共軛π電子的吸引,開始自我組裝,而這些被排列好的凝膠因子將在液晶晶胞中生成有秩序、具方向性的纖維狀網絡結構。 而我們發現,當此具有方向性的高分子網路形成於扭旋向列型液晶時,可使此液晶系統展現極佳的光電特性,有著能夠降低驅動電壓及穩定液晶分子以消除光學擾動的優點。另一方面,當此超分子液晶膠形成於反平行配向的液晶系統時,我們發現僅需要極低的電壓(約2.7 V),便可使此系統在凝膠因子的長鏈方向展現了極強的異向性散射之性質。並且,其所產生的異向性散射對比度更可高達1000:1。相對於傳統的液晶膠,我們呈現了一個具低操作電壓、高對比可切換的異向性散射裝置。 總結來說,我們認為此由凝膠因子在液晶中自我組裝而形成的超分子液晶膠展現了極大的潛力,在諸多的光電元件中提供了各種功能性應用,如低功耗顯示器、可調控式偏振片、半穿透半反射式顯示器、或是偏振光調制器等等。

並列摘要


Liquid crystal (LC) gels are widely used in various electro-optical devices, such as LC semiconductors with high mobility, rewritable memory of bistable states, and fast-response switching in twist nematic cells. In this dissertation, we present , we present , we present , we present , we present , we present , we present , we present , we present , we present , we present a new type of supramolecular LC physical gel which is formed through the fibrous self-assembly of the polyfluorene-based π-conjugated polymer in nematic liquid crystals. The supramolecular LC gels were prepared by uniformly mixing the LC molecules and the π-conjugated gelators. By heating the mixtures to isotropic state, the π-conjugated gelators would be well-dispersive in the liquid crystals. And then cooling down the mixtures to the required temperature, the supramolecular LC gels are formed by the gelation of the polymer molecules occurred through the π–π interactions between the π-conjugated gelator in the nematic phase of the LC host. We demonstrate that the orientated supramolecular structure can be formed through the fibrous self-assembly of the gelator in the nematic liquid crystal for the first time. With the utility of alignment layer, the gelator molecules can be aligned and form oriented polymer network through the template effect of the nematic LC host. The LC physical gels with oriented self-assembled supramolecular structures exhibit fantastic function in two LC systems. For the supramolecular LC gels formed in the twisted nematic liquid crystal cell we found that the presence of oriented polymer network makes the LC system demonstrate excellent electro-optical (EO) properties of driving voltage reduction and EO bump peak elimination. The polyfluorene-based supramolecular structures provide the functions of stabilizing LC molecules and improving the twisted nematic LC system. On the other hand, for the supramolecular LC gels formed in a cell with anti-parallel alignment layers, we found that the LC system exhibits significant anisotropic light scattering in the main-chain direction of the gelator molecules under an extremely low driving voltage (ca. only 2.7 V). In addition, the contrast ratio can be achieved as high as exceeding 1000. In contrast to the conventional LC physical gels, switchable anisotropic scattering devices with low operating voltage and high contrast ratio are demonstrated. In conclusion, we consider this supramolecular LC gel which is formed with functional self-assembled network provides great possibility for application in various electro-optical devices such as low power consumption displays, tunable polarizers, transflective displays, polarized light modulators, etc.

參考文獻


Ch1 References
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