;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.