| 摘要: | 現今科技日益進步，在液晶領域的研究發展趨於成熟，近年來持續開發新技術並應用在許多相關領域上。然而，近期環保的議題受到熱烈的討論及重視，許多團隊在各個不同領域投入大量人力進行節能減碳的相關研究，而在液晶顯示科技上，最直接的方法即為雙穩態的液晶顯示技術。近幾年來，有許多雙(多)穩態的液晶顯示技術已被開發，如利用膽固醇液晶多種穩態結構的特性、在外加直流電場下改變其自發性極化方向的表面穩定鐵電型液晶之雙穩態特性及液晶摻雜聚合物的多穩態技術等，而如何能達到多穩態且可重複使用的顯示元件，更是值得詳細探討與研究的課題。
本論文利用液晶摻雜自組成材料-十二氫氧基硬酯酸(HSA)，於基板表面塗佈光導體聚合物-聚乙烯基咔唑(PVK)薄膜之液晶盒中，製作多穩態且可重複抹除及寫入圖案的液晶顯示元件。其中，主要利用由氫鍵鍵結之HSA枝條結構穩固液晶分子排列，並由提高溫度使HSA之氫鍵斷裂，同時藉由PVK薄膜之光導體特性，經由照射紫外光使照光區域之液晶受外加電場影響而改變其排列方列，並在外加電場同時，將液晶盒溫度降溫以使HSA重新鍵結，最後關閉外加電壓，可得同時存在於液晶盒中的兩種液晶排列結構，故可將其應用在液晶顯示元件。本論文將分別討論以下三主題：
(1)自組成材料-HSA及光導體聚合物-PVK之特性；
(2)利用PVK薄膜及HSA製作TN結構之多穩態液晶顯示元件，該元件所顯示圖案的穩態液晶排列為照射紫外光區域之垂直結構，而背景為未照射紫外光區域之原TN結構，故在上下兩穿透軸相互正交偏振片下分別為暗態與亮態，如此即可顯示圖案。
(3)利用PVK薄膜及HSA製作多穩態散射型液晶顯示元件，該元件所顯示圖案的穩態液晶排列為照射紫外光區域之穿透態垂直結構，而背景為未照射紫外光區域所維持之原散亂結構，故其目視圖分別為穿透態與散射態，如此即可顯示圖案。
因此，本論文所提出多穩態液晶顯示元件之技術，其擁有可重複抹除及寫入圖案、利用光控及電控可達成灰階效果、低操作電壓及長時間穩態等特性之優點，故相信不僅可實際應用於顯示元件上，並可應用於許多液晶光學元件，如液晶光柵及液晶透鏡等。
;Nowadays, liquid crystal (LC) technology is getting more and more mature due to its novel developments and applications in many electro-optical fields. Recently, the issues of environmental protection are discussed and valued enthusiastically. Many scientists have been trying hard to pay much attention to the topics of carbon reduction from different viewpoints. In LC display (LCD) technology, the simplest technique is the development of bistable and multi-stable LCDs, such as the bistable textures of cholesteric LCs, the bistable properties of surface-stabilized ferroelectric LCs, multi-stable techniques of polymer network LCs, etc. Accordingly, it is worthwhile to develop the multi-stable and reusable display devices.
This study presents the multi-stable and reusable LC display devices using 12-hydroxysteric acid (HSA)-doped LCs in a poly(N-vinylcarbazole) (PVK) film-coated LC cell. It mainly adopted the reconnections of hydrogen-bond of HSA to form the branches to stabilize the LC structures. By increasing the temperature to that higher than the melting point of HSA, the strength of the intermolecular hydrogen bonds decreased so that the gelators were homogeneously dissolved into the LC host again. In the meantime, an external voltage was applied and the UV light was irradiated onto the LC cell through a photo-mask having the desired patterns simultaneously. The LCs in the regions with UV exposure reoriented toward the direction of the electric field due to the property of the photo-conductive PVK films. Thereafter, the LC cell was cooled down to room temperature and the hydrogen bonds reconnected automatically so that the gelators reassembled themselves in the direction of the reoriented LCs to stabilize the LC structures. Finally, two different structures in one LC cell were obtained, and such structures can also be used to demonstrate LC display devices. In this thesis, the following three parts are discussed in detail.
(1)The electro-optical properties of the self-assembly material-HSA and photoconductive polymer-PVK.
(2)Multi-stable LC display devices using HSA-doped LCs in a PVK film-coated LC cell. The two stable LC structures are the homeotropic structures in the regions with UV illumination and the twisted nematic structures in the regions without UV illumination. Then, the addressed patterns and their background observed under cross-polarizers present dark (homeotropic structures) and bright (twisted nematic structures) states, respectively.
(3)Multi-stable scattering mode LC display devices using HSA-doped LCs in a PVK film-coated LC cell. The two stable LC structures are the homeotropic structures in the regions with UV illumination and the scattering structures in the regions without UV illumination. Thus, the addressed patterns and their background present transparent state and scattering state, respectively.
Consequently, this study presents multi-stable LC display devices with the advantages of addressing, erasing, and re-addressing abilities, grayscale control, and so on. Considering the practical applications of the LC devices, they can be used not only in display devices but also in LC optical elements, such as LC gratings, LC lenses, and others. |
