摘要(英) |
Nowadays, liquid crystal (LC) technology is getting more and more mature due to its novel developments and applications in electro-optical fields. Recently, we would like to invent some new devices which can be applied to billboards, electronic tags, etc. By using bi-stable textures of cholesteric LCs, the structures can be chosen to be stabilized in the desired state. According to the experimental results, it shows that it can be kept in the desired state for more than two weeks.
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. Through the branches of hydrogen-bond of HSA, the structures of the cholesteric LC can be stabilized. By increasing the temperature over the melting point of HSA, the hydrogen bonds break down and HSA molecules dissolve in the LC host. If we keep increasing the temperature to the clearing point of the LC host, the cholesteric LC will turn into its isotropic state. With the application of suitable external voltages onto the LC cell at the temperature between the melting points of HSA and the clearing point of LC, we can get the focal conic state of cholesteric LC. Keep applying voltage onto the LC cell and then decrease the temperature of the LC cell to room temperature. After that, keeping at the room temperature and applying a suitable voltage onto the LC cell to make sure the structures are stable enough. Through the method described above, the LC cell will be kept in the state of the focal conic. If we decrease the temperature of the LC cell slowly without applying any voltage, the LC cell will present planar textures with the conditions of long pitch length and small cell gap. Because of the homogeneous alignment films, long pitch length, and small cell gap, the LC cell will tend to stay in the planar textures without applying any voltage. As the two methods mentioned above, the LC cell can have two different stable structures.
According to the method described above, PVK films are coated onto the LC cell and expose the PVK to UV light through a photo-mask having the desired patterns simultaneously. In the meantime, an external voltage is applied to the LC cell. The regions with UV exposure present focal conic textures, and the regions without UV exposure present planar textures. We cool down the temperature slowly and apply a suitable voltage simultaneously. Thereafter, the LC cell will have the pattern we want. |
參考文獻 |
[1] B. Bahaodur, Liquid crystals-applications and uses (World Scientific Press, 1990).
[2] O. Lehmam, “On flowing crystals,” Z. Phys. Chem. 4, 462 (1889).
[3] D. Dunmur and T. Sluckin, Soap, Science, and Flat-screen TVs: a history of liquid crystals (Oxford University Press, 2011).
[4] H. Ren, Y.-H. Fan, and S.-T. Wu, “Prism grating using polymer stabilized nematic liquid crystal,” Appl. Phys. Lett. 82, 3168 (2003).
[5] P. J. Collings and M. Hird, Introduction to liquid crystals chemistry and physics (Taylor & Francis Ltd, 1997).
[6] E. G. Virga, Variational theories for liquid crystals (World Scientific, 1993).
[7] I. C. Khoo and S. T. Wu, Optics and nonlinear optics of liquids (World scientific, 1993).
[8] O. Francescangeli, S. Slussarenko, and F. Simoni, “Light-induced surface sliding of the nematic director in liquid crystals,” Phys. Rev. Lett. 82, 1855 (1999).
[9] 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).
[10] H. Keller, “History of liquid crystals,” Mol. Cryst. Liq. Cryst. 21, 1 (1973).
[11] G. W. Gray, Thermotropic liquid crystals (New York: Wiley, 1987).
[12] W. H. de Jeu, Physical properties of liquid crystalline materials (Gordon & Breach, 1980).
[13] 謝承偉,表面配向對膽固醇藍相液晶光電特性影響之研究(國立中山大學物理研究所, 2011).
[14] D. K. Yang, X. Y. Huang, and Y. M. Zhu, “Bistable cholesteric reflective displays: materials and drive schemes,” Annu. Rev. Mater. Sci. 27, 117 (1996).
[15] S. Chandrasekjar, C. Frank, J. D. Litster, W. H. De Jeu, and L. Lei, Liquid Crystals of Disc-Like Molecules and Discussion, (the Royal Society, London, 1983).
[16] G. R. Fowles, Introduction to Modern Optic, 2nd ed., (University of Utah, New York, 1975).
[17] P. G. de Gennes and J. Prost, The physics of liquid crystals (Oxford University Press, 1993).
[18] L. M. Blinov and V. G. Chigrinov, Electrooptic effects in liquid crystal materials (Springer-Verlag Publishing Co., 1994).
[19]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).
[20] A. D. McNaught and A. Wilkinson, “Glossary of terms used in physical organic chemistry,” IUPAC, 66, 1123 (1994).
[21] N. Mizoshita, Y. Suzuki, K. Hanabusa, and T. Kato, “Bistable Nematic Liquid Crystals with Self-Assembled Fibers,” Adv. Mater. 17, 692-696 (2005).
[22] K. T. Cheng, Y. Tang, and C. K. Liu, “Electro-opto-thermal addressing bistable and re-addressable display device based on gelator-doped liquid crystals in a poly(N-vinylcarbazole) film-coated liquid crystal cell,” Opt. Express 24, 23572-23582 (2016).
[23] J. Stöhr, M.G. Samant, “Liquid crystal alignment by rubbed polymer surfaces: a microscopic bond orientation model,” J. Electron. Spectrosc. 98–99, 189–207 (1999).
[24] 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).
[25] 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).
[26] D. K. Yang and S. T. Wu, Fundamentals of Liquid Crystal Devices (John Wiley & Sons, Ltd., 2006).
[27] S. V. Pasechnik, V. G. Chigrinov, D. V. Shmeliova, Liquid Crystals: Viscous and Elastic Properies in Theory and Applications (John Wiley & Sons Press, 321, New York 2009).
[28] J. W. Doane, Polymer dispersed liquid crystal displays; Liquid crystals, applications and uses (World Scientific, Singapore, 1990).
[29] M. Mucha, “Polymer as an important component of blends and composites with liquid crystals,” Prog. Polym. 28, 837 (2003).
[30] J. Geng, C. Dong, L. Z. Ma, L. Shi, H. Cao, and H. Yang, “Electrically addressed and thermally erased cholesteric cells,” Appl. Phys. Lett. 89 081130 (2006).
[31] Andy. Y. G. Fuh, Z. H. Wu, K. T. Cheng, C. K. Liu, and Y. D. Chen, “Direct optical switching of bistable cholesteric textures in chiral azobenzene-doped liquid crystals,” Opt. Express 21, 21840-21846 (2013).
[32] P.-O. Bussiere, A. Rivaton, S. Therias, and J.-L. Gardette, “Multiscale Investigation of the Poly(N-vinylcarbazole) Photoageing Mechanism,” J. Phys. Chem. B. 116, 802-812 (2012). |