||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.
|| B. Bahoadur, Liquid crystals-applications and uses, (World Scientific Press, 1990).|
 F. Reinizer, “Beitrage zur kenntiness des cholesterins,” Monatsh. Chem. 9, 421 (1888).
 O. Lehmam, “On flowing crystals,” Z. Phys. Chem. 4, 462 (1889).
 P. J. Collings, and Michael Hird, Introduction to liquid crystals chemistry and physics, (Taylor ＆ Francis Ltd, 1997).
 E. G. Virga, Variational theories for liquid crystals, (Chapman & Hall London, 1994).
 I. C. Khoo and S. T. Wu, Optics and nonlinear optics of liquid crystals, (World Scientific, 1993).
 O. Francescangeli, S. Slussarenko, and F. Simoni, “Light-induced surface sliding of the nematic director in liquid crystals,” Phys. Rev. Lett. 82, 1855 (1999).
 M. Marinelli and F. Mercuri, “Effects of fluctuations in the orientational order parameter in the cyanobiphenyl (nCB) homologous series,” Phys. Rev. E 61, 1616 (2000).
 H. Keller, “History of liquid crystals,” Mol. Cryst. Liq. Cryst. 21, 1 (1973).
 G. W. Gray, Thermotropic liquid crystals, (Wiley, New York 1987).
 W. H. de Jeu, Physical properties of liquid crystalline materials, (Gordon & Breach, 1980).
 松本正一，角田市良，液晶之基礎與運用 (國立編譯館, 1996).
 P. Yeh and C. Gu, Optics of liquid crystal displays, (John Wiley ＆ Sons, Inc., 2006).
 G. R. Fowles, Introduction to modern optics, 2nd ed., (University of Utah,
 P. G. de Gennes and J. Prost, The physics of liquid crystals, (Oxford University Press, 1993).
 L. M. Blinov and V. G. Chigrinov, Electrooptic effects in liquid crystal materials, (Springer-Verlag Publishing Co., 1994).
 M. Hara, H. Takezoe, and A. Fukuda, “Forced Rayleigh scattering in nCB′s (n=5-9) with methyl red and binary mass diffusion constants,” Jpn. J. Appl. Phys. 25, 1756 (1986).
 郭怡君，利用膽固醇凝膠製作多穩態和可調液晶光柵之研究 (國立成功大學物理研究所, 2011).
 張志榮，氫氧基硬酯酸參雜向列型晶材料之多重穩態特性及其應用之研究 (國立成功大學物理研究所, 2011).
 M. Kaczmarek and A. Dyadyusha, “Structured, photosensitive PVK and PVCN polymer layers for control of liquid crystal alignment,” J. Nonlinear Opt. Phys. Mater. 12, 547 (2003).
 K. Nakajima, H. Wakemoto, S. Sato, F. Yokotani, S. Ishihara, and Y. Matsuo, “Polystyrene derivative films for liquid crystal alignment,” Mol. Cryst. Liq. Cryst. 180, 223 (1990).
 H. Bolink, “Photorefractive Polymers,” University of Groningen, Netherlands. (1997).
 施敏 著，黃調元 譯，半導體元件物理與製作技術 (國立交通大學出版社, 2002).
 H. Mada and K. Osajima, “Time response of a nematic liquid‐crystal cell in a switched dc electric field,” J. Apply. Phys. 60, 3111 (1986).
 A. Sugimura, N. Matsui, Y. Takahashi, H. Sonomura, H. Naito, and M. Okuda, “Transient currents in nematic liquid crystals,” Phys. Rev. B 43, 8272 (1991).
 A. Mochizuki, T. Yoshihara, K. Motoyoshi, and S. Kobayashi, “An electric bilayer model of the transient current in a nematic liquid crystal cell,” Jpn. J. Appl. Phys. 29, 322 (1990).
 H. Jin, Y.-B. Hou, X. G. Meng, A. W. Tang, and F. Teng, “Photoconductive properties of PVK:Alq3 blend films studied by steady-state and time-resolved transient photocurrent spectra,” Chinese J. Polym. Sci. 26, 249 (2008).
 陳園迪，聚乙烯基咔唑薄膜式液晶元件之特性：配向效應、熱反應、相位分離及其新穎應用 (國立成功大學物理研究所, 2012).
 陳可南，利用液晶薄膜製造先進可電控光圈之研究 (國立成功大學物理研究所, 2014).
 Y. D. Chen, A. Y. G. Fuh, and K. T. Cheng, “Particular thermally induced phase separation of liquid crystal and poly(N-vinyl carbazole) films and its application,” Opt. Express 20, 16777 (2012).
 P. Yeh and C. Gu, “Optics of Liquid Crystal Display”, John Wiley and Sons, New York (1999).
 C. Mauguin, “Sur les cristaux liquids de Lehman,” Bull. Soc. Franc. Mineral. 34, 71 (1911).
 C.H. Gooch and H. A. Tarry, “The optical properties of twisted nematic liquid
crystal structure with twist angles≤90°,” J. Phys. D: Appl. Phys. 8, 157 (1975).
 J. W. Doane, “Polymer dispersed liquid crystal displays; Liquid crystals, applications and uses,” (World Scientific, Singapore, 1990).
 M. Mucha, “Polymer as an important component of blends and composites with liquid crystals,” Prog. Polym. 28, 837 (2003).
 G. P. Crawford and S. Z ̌umer, “Liquid Crystals in Complex Geometries --- Fromed by polymer and porous networks,” (Taylor and Francis, London 1996).
 葛聰智，聚合物穩定膽固醇液晶結構薄膜光電特性及繞射現象之研究 (國立成功大學物理研究所, 2003).
 J. Geng, C. Dong, L. Zhang, Z. Ma, L. Shi, H. Cao, and H. Yang, “Electrically addressed and thermally erased cholesteric cells,” Appl. Phys. Lett. 89, 081130 (2006).