紫外光線偏振狀態對光敏膽固醇液晶解旋程度的影響

Effect of Linear Polarization State of Ultraviolet Light on the Unwinding of Photoresponsive Cholesteric Liquid Crystals

楊文溢(Wen-Yi Yang)

指導教授 ： 李偉

國立交通大學/光電學院/影像與生醫光電研究所/碩士(2020年)

摘要

本研究對象為摻有光控偶氮旋光劑的向列型液晶所形成的膽固醇型液晶，探討不同線偏振狀態的紫外光如何影響液晶的螺距或旋性及其光反應時間特性。有別於傳統的光控型液晶，我們不需要特別控制紫外光強度或更換光源來進行光調控或狀態切換—即調控膽固醇液晶的螺旋扭轉力，或使用紫外光及綠光來達到可逆的狀態切換過程。在此我們簡單地改變單一波長紫外線偏光的偏振角，便可控制膽固醇液晶的螺旋扭轉力，達到手性切換模式—膽固醇平面態、（超）扭轉向列態及水平向列態。吾人使用偏光顯微鏡觀察液晶的光學紋理圖，利用光穿透率隨曝光時間變化的量測，觀察紫外光線偏振角如何影響實驗結果。本論文同時就實驗中的切換機制，應用既有的理論以及模擬進行討論。最後吾人提出一些延伸實驗，證明藉由調控線偏振光的角度，即可進行扭轉與水平向列態間的切換¬；由實驗數據計算出各個樣品在上述兩種狀態間的切換時間，可發展作為未來光電元件的應用。

關鍵字

紫外光 ； 偏振 ； 偶氮 ； 光敏 ； 液晶

並列摘要

This thesis demonstrates the effect of linearly polarized ultraviolet (UV) light on the photo-induced texture transition in a cholesteric liquid crystal (CLC). In this study, we doped azo-chiral molecules into nematic liquid crystal to obtain a CLC phase. Exploiting the photo-tunable characteristic of azo-chiral materials, we were able to control the helical twisting power (HTP) with linearly polarized UV light irradiation through the photo-induced trans–cis isomerization. Generally, the HTP of azo-chiral molecules can be tuned by irradiation with different exposure time, wavelength and intensity, and the process is reversible. In this research, we demonstrated a simpler way to tune the HTP of CLC. Employing linearly polarized UV light, we were able to switch the sample more efficiently between three steady state, that is planar-state (CLC), twist-state (T) and planar-nematic (N) state. The optical textures can be observed by polarized microscope (POM). In additional, we measured the time-dependent transmittance curve to investigate the different effect via the varied linearly polarized UV light. Moreover, we confirmed the phenomenon by simulation software and twisting nematic liquid crystal display theory. Finally, we can switch between the planar-nematic state and twist-state via different polarizing angle of the linearly UV light. With the calculation of response time, we were able to have applicable samples. In conclusion, this research proposed an idea of possible future development.

並列關鍵字

ultraviolet ； polarization ； azo ； photoresponsive ； liquid crystal

參考文獻

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