BHN液晶盒之溫度效應

Temperature effect on Bistable Chiral Tilted-Homeotropic Nematic Liquid Crystal Cells

黃旻暄(Min-Hsuan Huang)

指導教授 ： 徐芝珊

中原大學/理學院/應用物理研究所/碩士(2010年)

https://doi.org/10.6840/CYCU.2010.00590

摘要

摘要
本論文在探討溫度對雙穩態液晶顯示器BHN-LCD（Bistable Chiral Tilted-Homeotropic Nematic Liquid Crystal Display）在液晶參數、外觀與雙穩態上所產生之影響。
現今的雙穩態液晶顯示器的發展以可攜帶式為主，因BHN-LCD具有低驅動電壓、高對比度和使用傳統製程製造的三大優點，其雙穩態是否因外在環境溫度改變而產生顯示上的變化為重要的研究課題。
論文的第一部份為研究BHN液晶顯示器所使用的雙頻液晶MLC-2048，其物理特性隨溫度的變化。其中包括液晶參數，如︰液晶複折射率（birefringence）、彈力常數（elastic constants）、黏滯係數（viscosity coefficients）、介電異方性（dielectric anisotropy）、螺距（pitch）....等。而第二部份為探討在不同的環境溫度下，BHN液晶顯示器穩態的穩定性、操作和顯示畫面的改變。
我們利用量測液晶盒相位延遲隨溫度的改變，得知MLC-2048之複折射率和秩序參數隨溫度上升而下降。並由秩序參數推得彈力常數與黏滯係數與溫度之關係。此外，分別使用水平與垂直排列液晶盒，量測液晶盒之電容值與外加電壓頻率、溫度之關係，進而得知雙頻液晶MLC-2048之介電異方性隨著溫度升高，其與頻率關係的曲線與交互頻率（cross frequency）均往高頻方向移動。而在摻雜對掌性物質ZLI-811時，由觀察楔型液晶盒發現其螺距隨溫度上升而增加。
在外觀上，BHN液晶盒之BT和T態的穿透光譜隨溫度上升會有向高頻移動的現象，兩穩態之切換時間會明顯減少，且出現T態不穩定之情形。我們利用之前分析的液晶參數隨溫度之關係，帶入模擬程式，分析並解釋。

關鍵字

液晶 ； BHN ； 溫度

並列摘要

Abstract
In this thesis, we analyze the influence of temperature on BHN-LCD, including the appearance, stability and switching processes through the temperature effect on the liquid crystal MLC-2048.
In the first part of the thesis, we derive the birefringence and order parameter of MLC-2048 by measuring the phase retardation as a function of temperature in the lab-made homogeneous LC cells. Then using the order parameter which decreases as the temperature increases, we have the relationships between temperature and the elastic constants, rotational and shear viscosities. The dielectric constant and corresponding cross frequency are obtained by measuring the capacitances as functions temperature and the frequencies of the applied voltages in the homogeneous and vertically aligned cells. Finally, we used the disclination lines in wedge cells to calculate the pitches which increase when the temperature rises.
In the second part of the thesis, the switching response time between two states decrease and the appearance of the BHN LC cell changes color slightly when the temperature increases. However, the stability of the Twisted state decreases. By analyzing the energy barriers between two stable states through the LC parameters as functions of temperature in the simulation, we conclude that the reason for the instability of Twisted state are because the energy barriers decrease and are unbalanced as the temperature rises.

並列關鍵字

liquid crystal ； BHN ； temperature

參考文獻

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