微胞式膽固醇液晶於可撓式基板之雙軸拉伸之研究

The Influence of the Bi-axial Stretching on the Encapsulated Cholesteric Liquid Crystal on the Flexible Substrate

金軒甫(Hsuan-Fu Chin)

指導教授 ： 劉育松

國立虎尾科技大學/電機資訊學院/電子工程系碩士班/碩士(2012年)

摘要

本論文為利用單基板製程製備一微胞式膽固醇液晶薄膜，此薄膜具有高撓曲可塑性、快速製程、低損耗等優良特性，並可搭配卷對卷製程進行大面積生產，極適合應用在電子紙、海報等應用上。
在本論文中，我們利用經乳化法形成的均勻的液晶微胞進行製備，為使薄膜的拉伸特性最佳化，並找出最合適的製備參數，在膽固醇液晶材料中添加增塑劑，並使用PEDOT:PSS取代傳統ITO作為電極層來降低傳統ITO昂貴且易脆的特性，並嘗試使用多種基板來製備，希望不管在傳統2維平面顯示器或是未來的3維立體顯示器上皆有其發展運用空間，實驗結果發現添加增塑劑無法有效提升液晶的拉伸特性，需降低樣品溫度才有助於提高樣品的拉伸特性，故溫度才是影響液晶薄膜拉伸特性的主因。
使用雙軸拉伸系統觀察樣品的應力-應變圖，並同時對樣品升溫，利用反射光譜觀察溫度對拉伸率的影響。實驗結果發現，溫度越高，由於液晶乾燥造成脆化使樣品產生龜裂，planar及focal conic兩態間反射率差的最大拉伸率隨之降低，所以我們使用一常溫下即可拉伸的TPU基板取代須在高溫下才可軟化拉伸的APET基板進行製備，實驗結果發現在常溫下在拉伸率20%時仍可維持良好的反射特性且不會形成龜裂現象。
量測常溫下拉伸率對反射率光譜的影響。結果顯示當拉伸率上升時，由於微胞式膽固醇液晶產生形變，會使planar及focal conic的反射光強度有上升的現象，故針對微胞形變方向進行討論，實驗結果發現入射光入射方向平行於微胞形變方向的反射率光譜在大角度時會迅速下降至比未拉伸前的試片反射率還低，反之入射光入射方向垂直於拉伸方向的反射率光譜在大角度時下降幅度與未拉伸前的反射率曲線一致。
液晶微胞形狀會會影響反射率光譜，未乾燥前的微胞液晶呈現出圓球狀，此時反射率光譜反射波長範圍較廣，液晶薄膜呈現近白色；而經乾燥後，由於液晶微胞受重力等因素而經壓縮相互擠壓導致形變成較近橢圓形的微胞，此時反射率光譜反射波長範圍較窄，呈現一較明顯波峰，液晶薄膜呈現黃綠色。

關鍵字

膽固醇液晶 ； 乳化法 ； 單基板 ； 雙軸拉伸

並列摘要

In this study, we prepared a encapsulated cholesteric liquid crystal by emulsion method on the flexible and single substrate, and tried to find a best process include adding workability agent or using PEDOT:PSS which can replace ITO as the electrode layer to avoid the properties which ITO is expensive and weak .We also prepared other substrates and expect to develop in 2-D and 3-D display.
Use biaxial-stretching system to observe the stress-strain, and use optical measuring system to observe the reflected spectra in high temperature. In our results, film will chap cause damage in high temperature environment (70°C ~76°C) and lead to no driving and the strain of liquid crystal film will increase in lower temperature. Then, we use a new flexible substrate, thermoplastic polyurethane (TPU) for the fabrication of liquid crystal film and measuring the reflectivity spectra at normal incidence in biaxial-stretching. We observed that the reflectivity will increase in whit light incident with strain increase. Use optical microscope to observe the liquid crystal film in uniaxial- stretching, the liquid crystal droplets were changed with stretching direction. The droplets deformed from circle to oval.
We measure the reflectivity spectra at normal incidence of cholesteric liquid crystal film which was stretched and stretched before at different angles. When the angle is 0° between incident light and normal line of the cholesteric liquid crystal film, the reflectivity of film which was stretched is higher than stretched before, because the reflect area of encapsulated cholesteric liquid crystal droplets is lager after stretch. When angle between incident light and normal line of the cholesteric liquid crystal film which was stretched increase, the reflectivity of incident light parallel to stretching direction is lower than film which was stretched before and incident light plumb to stretching direction. We also observe that the droplets would deform after coating and lead to reflectivity spectra at normal incidence would be change from broad wavelength range to narrow.

並列關鍵字

Cholesteric Liquid Crystal ； Emulsion method ； Single substrate ； biaxial-stretching system

參考文獻

[1]S. T. Wu and D. K. Yang, 2001, "Reflective Liquid Crystal Displays ", Wiley, New York.

[2]E. Nakamura et al., 1998, "Development of electrophoretic display using microcapsulated suspension", SID Symposium Digest 29, pp. 11014–1017.

[3]Krishnan Chari, Charles M. Rankin, David M. Johnson, Thomas N. Blanton, and Robert G. Capurso, 2006, "Single-substrate cholesteric liquid crystal displays by colloidal selfassembly ", APL, 88, pp. 043502.

[8]林宗賢，2004，"液晶光子晶體雷射現象與其光控制研究"，國立成功大學物理研究所碩士論文。

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