具光學三穩態之雙頻層列A型液晶元件

A Tristable Dual-Frequency Smectic-A Liquid Crystal Device

王上和(Shang-Ho Wang)

指導教授 ： 李偉

國立交通大學/光電學院/照明與能源光電研究所/碩士(2020年)

摘要

本論文提出一個以頻率做切換的電控三穩態雙頻層列A型液晶元件，並研究各相態之紋理、光學特性以及各結構狀態之間切換的驅動機制。首先在雙頻向列液晶（HEF-951800）中摻雜特定濃度的手性分子（S811），藉此誘導出混合材料的層列相；確保各狀態之穩定性後，再由介電頻譜術測得雙頻液晶之反轉頻率，並找出適當的頻率使介電各向異性在正值與負值之間轉換，以使平面態與垂直態兩狀態間能直接且可逆切換。接著吾人利用垂直態時介電鬆弛所產生的介電加熱效應，使液晶從層列相升溫至扭曲晶界相，在此相中液晶無法有秩序地維持垂直排列並且開始散亂傾倒，此時關閉電壓停止介電加熱效應，液晶由扭曲晶界相轉換到層列相；由於此時液晶分子的排列散亂而無秩序性，因而形成混亂排列的焦錐態，此即為本研究所提出的第三個穩態。

關鍵字

雙頻液晶 ； 層列型液晶 ； 三穩態 ； 介電加熱 ； 扭曲晶界相

並列摘要

In this thesis, we proposed a frequency-dependent electrically controlled tristable dual-frequency Smectic-A liquid crystal device. The textures, optical properties and driving mechanism between each state are studied. At first, the smectic-A (SmA*) phase was induced by doping the chiral dopant (S811) at a specific concentration in the dual-frequency liquid crystal (DFLC). After the stability of each state is checked, the crossover frequency (fc) of DFLC is measured by the dielectric spectrum technique, and the appropriate frequency is found to make the dielectric anisotropy change between positive and negative, so that the planar and homeotropic states can be switched directly and reversibly. Then, by using the dielectric heating effect generated by the dielectric relaxation under homeotropic state, the LCs is heated from SmA* phase to the twist grain boundary A (TGBA*) phase. In this phase, the LC molecules cannot maintain the vertical orientation and begins to tumble randomly. At this time, the voltage is turned off to stop the dielectric heating effect, and the LC is transformed from the TGBA* to the SmA*. Due to the disordered orientation of LC molecules, thus forming into focal-conic state, which is the third stable state proposed by this study.

並列關鍵字

DFLC ； Smectic-A ； Tristable ； dielectric heating ； TGBA

參考文獻

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