| 摘要: | 本論文探討了透過頻率電壓調控由摻雜液晶二聚體之膽固醇液晶所形成之均勻橫向螺旋(Uniform Lying Helix, ULH)結構的光學特性，主要目的是分析並優化這些結構在反射式電子紙顯示器中的應用，以提高顯示對比度和性能。本論文研究內容分為兩部分，第一部分探討未摻雜及摻雜液晶二聚體(CB7CB)的膽固醇液晶在不同厚度液晶盒中的特性變化，在未摻雜CB7CB的膽固醇液晶於不同厚度液晶盒的特性影響研究發現，隨著液晶盒厚度從3.22 μm增加至5.25 μm，整體穿透率降低，其電光特性也發生顯著改變，進而影響顯示效果；而摻雜CB7CB的膽固醇液晶在三種不同反射光波段(RGB)中的表現，透過適當的電壓和頻率控制，可誘導形成穿透率約為53%的焦錐態及穿透率約為82%的ULH結構，此結構在增加前向散射(Forward scattering，最佳提升約29%)方面表現出顯著的優勢，摻雜CB7CB的液晶在不同螺距下(399 nm、335 nm及267 nm)的整體穿透率和結構特性存在些微差異。
第二部分則深入探討摻雜液晶二聚體對膽固醇液晶的光電特性影響，首先分析摻雜液晶二聚體後的膽固醇液晶對反應時間的影響，並對施加直流電場或低頻交流電場的反應時間進行量測。結果顯示摻雜CB7CB對比未摻雜CB7CB能有效縮短反應時間約8秒，且在適當頻率及電場下，螺距越小對反應時間縮短越顯著，最短反應時間約為一秒內。另亦透過實驗發現CB7CB對灰階顯示的效果也有些微提升，若在適當的d/p值(d/p = 12，其中d為液晶盒厚度，p為螺距)及電壓與頻率下，穿透率表現最為線性(電壓-穿透率曲線接近斜直線)，且最高穿透率(82%)與最低穿透率(53%)差異最大，灰階調控效果較佳。本論文另釐清透過摻雜離子材料(SDS)是否亦能增強動態散射效果並降低反應時間，以及摻雜不同液晶二聚體(CB11CB)觀察其對膽固醇液晶的影響。由實驗結果顯示上述方法皆無法使膽固醇液晶形成ULH結構。
;This thesis reports on the optical properties of uniform lying helix (ULH) structures generated by the application of electric fields with different frequencies and by doping liquid crystal (LC) dimers into cholesteric LCs (CLCs), the structure is used to enhance forward scattering (light scattering towards the photodetector) and reduce backward scattering (light scattering towards the observer), thereby enhancing display contrast. The thesis is divided into two parts, with the primary objective of analyzing and optimizing the CLC structures for applications in electronic papers of reflective mode displays to enhance contrast and performance.
In the first part of the experiment, the properties of undoped and CB7CB-doped CLCs filled into LC cells with different cell gaps were studied. First, the overall transmittance decreases with the increase of cell gap, such as from 3.22 μm to 5.25 μm. The influences of the LC cell gap on the electro-optical properties of CLCs without doped LC dimers significantly affect display performance. Additionally, the performance of CB7CB-doped CLCs with three different reflective light spectra (RGB) was analyzed in detail. With appropriate voltage and frequency control, focal conic (FC) structures with a transmittance of approximately 53% and ULH structures with a transmittance of approximately 82% can be achieved. These structures demonstrated significant advantages in enhancing forward scattering (the best improvement of roughly 29%) from the CLC structures. The differences in overall transmittance and structural properties were also examined using CB7CB-doped CLC with different helical pitches, such as 399 nm,335 nm, and 267 nm).
The second part of the experiment delved into the impacts of doping LC dimers on the optoelectrical properties of CLCs. First, the effect of doping LC dimers on the response time of CLCs was analyzed. The response times of LCs applied with electric fields with direct current or low-frequency alternating current were measured. The experimental results indicated that doping CB7CB effectively shortens the response time by approximately 8 seconds compared to the undoped CB7C. Moreover, at suitable frequencies and electric fields, a smaller pitch length significantly enhanced the reduction in response time, with the shortest response time being approximately within one second. Additionally, experimental findings revealed a slight enhancement in grayscale display effectiveness with CB7CB. Optimal grayscale modulation was observed under suitable d/p ratios (d/p = 12, d represents the LC cell gap, and p represents the pitch), applied voltages, and frequency conditions. The transmittance shows the highest linearity, with the greatest difference between the highest transmittance (82%) and the lowest transmittance (53%), resulting in better grayscale control (voltage-transmittance curve is close to a oblique straight line). Furthermore, the study also explored whether doping ion materials (SDS) could enhance dynamic scattering and reduce response time. The impact of another LC dimer, CB11CB, doped into CLCs was also examined. Unfortunately, the experimental results showed that the ULH structures cannot be generated using these methods. |
