聚合物穩固電致變色液晶之光電特性及其應用;Electro-optical characteristics of polymer stabilized electrochromatic liquid crystals and their applications

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题名:	聚合物穩固電致變色液晶之光電特性及其應用;Electro-optical characteristics of polymer stabilized electrochromatic liquid crystals and their applications
作者:	林芯瑋;Lin, Sin-Wei
贡献者:	光電科學與工程學系
关键词:	液晶;二色性染料;Liquid crystal;Dichroic dye
日期:	2023-08-11
上传时间:	2024-09-19 15:49:22 (UTC+8)
出版者:	國立中央大學
摘要:	因電致變色元件具有低耗能、高對比度與可撓性強等特性，在顯示領域中受到廣泛的關注，本論文欲應用電致變色特性於液晶顯示元件中，故選用電致變色液晶SLC1717，其可與離子液體在直流電場下發生氧化還原反應，當SLC1717被氧化後會吸收綠光波段而在顯示元件中呈現洋紅色。本論文探討其著色態(氧化態)與離子液體[Bmim][NTf2]之濃度的相關性，並提出98 wt% SLC1717與2 wt% [Bmim][NTf2]混合為最佳濃度比，在SLC1717第一氧化態的吸收峰值波長518.4 nm下有最大穿透度變化量57.33%。在實驗過程中發現長施間施加直流電場或是久置液晶盒後，[Bmim][NTf2]會對SLC1717產生自發性垂直配向力，即使在基板鍍有水平配向膜下，依然會破壞液晶之水平排列，故嘗試以聚合物網絡結構穩固液晶之水平排列，並對其穩固效果作分析，在[Bmim][NTf2]濃度較高(2 wt%)的聚合物穩固電致變色液晶中，施加多次或是長時間的直流電場會使液晶盒呈現散射，推測是由垂直配向力與水平配向力同時作用下使液晶的排列形成多區域所造成。因此本論文降低聚合物穩固電致變色液晶中離子液體的濃度(0.5 wt%)以降低其自發性垂直配向力，而施加多次或是長時間的直流電場後，可由顯微影像與目視圖發現液晶盒不再呈現散射。最後本論文於聚合物穩固電致變色液晶中摻雜二色性染料AC1，根據賓主效應以交流電控制AC1之顏色深淺變化，另以直流電控制SLC1717氧化態的顏色深淺變化，可在一個元件中同時呈現電致變色特性與液晶之光電特性。;Electrochromic devices have attracted remarkable attention in the display field due to their low energy consumption, high contrast, and excellent flexibility. This thesis attempts to apply electrochromic characteristics to liquid crystal (LC) displays by using the electrochromic LC, SLC1717. In the presence of a direct current (DC) electric field, SLC1717 undergoes a redox reaction with the ionic liquid [Bmim][NTf2], and the color of SLC1717 will turn to magenta from colorless after its oxidation process. This study investigates the relation between the colored state (oxidized state) of SLC1717 and the concentration of the ionic liquid [Bmim][NTf2], and proposes the optimal concentration ratio is 98 wt% SLC1717 and 2 wt% [Bmim][NTf2], which possesses the maximum dynamic range of transmission (57.33%) at the wavelength of absorption peak (518.4 nm) with the application of a DC electric field. According to the experimental results about the electrochromic characteristics of SLC1717, it was observed that multiple or long-time applications of DC electric field cause [Bmim][NTf2] to provide SLC1717 with an anchoring of vertical alignment and thereby disrupt the homogeneous alignment of the LCs, indicating that the anchoring provided by the coated homogeneous alignment film is disrupted. To stabilize the homogeneous alignment of the adopted LCs, the polymer network structures were introduced and analyzed for their stabilization effect. In the polymer-stabilized electrochromic LCs with a higher concentration of [Bmim][NTf2] (2 wt%), multiple or long-time applications of DC electric field lead to scattering. The scattering drawback is speculated that the formation of multi-domains from the competition of vertical and homogeneous alignment anchoring. Therefore, we reduced the concentration of [Bmim][NTf2] in the polymer-stabilized electrochromic LCs to reduce the anchoring force from the spontaneous vertical alignment and thereby overcomed the scattering problem. The above results were also verified through polarized optical microscopy and photographs. Finally, we doped AC1 into the polymer-stabilized electrochromic LCs to evaluate the color changes by dichroic dyes and electrochromic LCs. According to the guest-host effect, the color change of AC1 can be controlled by using alternating current (AC) electric fields, while that of the oxidized state of SLC1717 can be controlled by using DC electric fields. This allows the device to simultaneously exhibit both the electrochromic characteristics and the electro-optical properties of LCs.
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