摩擦配向角對於膽固醇液晶光電特性之影響:以橫向螺旋態為焦點

Impact of the Rubbing Angle on the Electro-Optical Characteristics of Cholesteric Liquid Crystals: Focusing on the Uniform Lying Helix State

高義修(I-Hsiu Gau)

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

本研究之目的為探討配向角度對於膽固醇液晶橫向螺旋態光軸之排列與光電特性。其研究手法是以摩擦法對基板進行表面處理，並採用垂直配向模式在各配向角之空液晶盒；在注入膽固醇液晶後，利用降電壓法與電流體效應形成橫向螺旋態，透過穿透光譜與觀察光學紋理，判斷不同配向角之液晶盒在橫向螺旋態時的光軸變化。
由實驗結果得知，摩擦方向與光軸之夾角ϕ受到配向角γ所控制，且該夾角變化滿足關係式ϕ = γ/2  90。當上下基板的配向夾角在設定為30至0與150至180的數值時可獲得均勻橫向螺紋態，其餘配向角皆造成受抑的橫向螺旋結構，產生雙疇域橫向螺旋紋理。此外，本研究也探討三種不同配向模式對於橫向螺旋態、平面態膽固醇液晶之均勻性與垂直態切換電壓的影響，並得出結論可知在垂直模式下，能夠大幅降低液晶盒之驅動電壓。

關鍵字

橫向螺旋態 ； 膽固醇液晶 ； 垂直配向液晶盒 ； 磨擦配向角 ； 光軸

並列摘要

In this thesis, the optical axis (O.A.) of the uniform lying helix (ULH) state and electro-optical properties of the cholesteric liquid crystal (CLC) cells with distinct rubbing angles were investigated. Homeotropically aligned CLC cells with various rubbing angles were fabricated using the conventional mechanical rubbing method. The ULH state was formed by means of the decreasing voltage method proposed by our group and electrohydrodynamic effect after the CLC was injected into the empty cells. Both the measurement of transmission spectra and the observation of polarizing optical textures were carried out for each CLC cell to identify the effect of the rubbing angle on the O.A. of the ULH state.
Experimental results suggest that the O.A. of the CLC cell in the ULH state can readily be controlled by the rubbing angle γ. That is, the angle ϕ between the rubbing direction and the O.A. of the cell in the ULH state satisfies the relation ϕ = γ/2  90. Well-aligned ULH states were observed when the rubbing angles lie between 30 to 0 and 150 to 180 whereas the other rubbing angles beyond these two ranges led to a suppressed ULH structure, yielding two-domain ULH texture. Finally, three distinct aligned cell modes were investigated to compared their impacts on the contrast ratio and switching voltage from the ULH or Grandjean planar state to the homeotropic state. Our results indicate that the vertical-alignment cell mode enables a substantial reduction in switching voltage to reach the homeotropic texture.

並列關鍵字

Uniform lying helix ； cholesteric liquid crystals ； vertical-alignment cell mode ； rubbing angle ； optical axis

參考文獻

[1] F. Reinitzer, “Beiträge zur kenntnis des cholesterins,” Monatshefte für Chemie 9, 421–441 (1888).

[2] O. Lehmann, “Über fliessende Krystalle,” Zeitschrift für Physikalische Chemie 4, 462–468 (1889).

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[4] H.-S. Kitzerrow and C. Baher, Chirality in Liquid Crystals, (Springer, New York, 2001).

[5] 松本正一、角田市良，劉瑞祥譯，《液晶之基礎與應用》，國立編譯館，台北，民85年。