以電熱調控膽固醇液晶之光子能隙

Electro-Thermal Tuning of Photonic Band Gap in Cholesteric Liquid Crystal

陳俊男(Chun-Nan Chen)

指導教授 ： 蔡淑雲

國立臺北科技大學/機電學院/光電工程系所/碩士(2010年)

https://doi.org/10.6841/NTUT.2010.00515

摘要

本實驗研究，向列型液晶E7 掺雜手性分子S811混合形成的膽固醇液晶，此種膽固醇液晶具有螺旋結構，膽固醇液晶形成自聚集週期性螺旋結構，就如同一維光子晶體，光子晶體最重要的特性就是選擇性反射，螺距和膽固醇液晶平均折射率將會影響選擇性反射。我們使用自製的溫度控制儀器，精確控制膽固醇液晶樣品的溫度，觀察到手性分子濃度會影響螺距和相轉移溫度，並且量測計算膽固醇液晶在膽固醇相的螺距，發現手性分子掺雜比例嚴重影響膽固醇相選擇性反射，我們引用Keating’s model解釋溫度與螺距的關係，透過偏光顯微圖(polarization optical microscopy, POM)與示差掃描熱量分析儀(differential scanning calorimetry, DSC)觀察到液晶相態變化。如果選擇適當比例的膽固醇液晶時，將可以完美的調控指定波長達467nm~2123nm範圍。增加外部電壓會造成螺距層數減少，由於反射光的反射強度取決於螺距層數量，表示反射率隨著增加電壓而下降。

關鍵字

膽固醇液晶 ； 向列型液晶 ； 手性分子 ； 螺距 ； 轉移溫度

並列摘要

In this study, Cholesteric liquid crystals were prepared by mixing a nematic liquid crystal (E7) and a chiral compound (S811). Cholesteric liquid crystals (CLC) have a self-organized periodic helical structure; the CLC is regarded as a one-dimensional photonic crystal, the selective reflection band dependence of the pitch and average refractive index of the CLC. We are able to measure the helical pitch in cholesteric phase. We observe what difference in helical pitch and phase transition temperature depend on the concentration of chiral compounds. The sensitivity of the selective reflection band of the cholesteric phase to the thermal tuning depends strongly on the ratios of the chiral dopants. When fitted by the Keating’s formula, the helical pitch calculated from our experimental results lies on the predicted curve. The LC phases were characterized by polarization optical microscopy and differential scanning calorimetry (DSC) techniques. The optimized ratios of the mixture CLCs for the optimized reflection band with the specified wavelength ranging form 467 nm to 2123 nm have been suggested. The number of pitches within the cholesteric decreases with increasing voltage. As the intensity of the reflection depends on the number of pitches along the light path the reflection shows a decrease with increasing voltage.

並列關鍵字

Cholesteric liquid crystals ； Nematic liquid crystal ； Chiral ； Pitch ； Transition temperature

參考文獻

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