Supertwisted nematic liquid crystal

H. Seiberle and M. Schadt, LC-conductivity and cell parameters their influence on twisted nematic and supertwisted nematic liquid crystal displays. Mol. Cryst. Liq. Cryst. 239(1), 229-244, (1994). 

Fast Responding Supertwisted Nematic Liquid Crystal Displays.219... 

Odai, H., Hanami, T., Hara, M., Iwasa, K., and Tatsumi, N., Optical compensation of supertwisted nematic liquid crystal displays applied by polymer retardation film, Proc. 8th Int. Display Research Conference, 195, 1988. 

Supertwisted nematic display, 15 114 Super twisted nematic liquid crystal display (STN-LCD), 9 340 Super ultra-low emissions vehicle (SULEV), 13 855... 

Figure 6.1 Optically bistable, photoaligned, supertwisted nematic LCD [1]. Reproduced from M. Stalder and M. Schadt, Photoaligned bistable twisted nematic liquid crystal displays. Liquid Crystals 30, 285 (2003)...

Thermotropic cholesterics have several practical applications, some of which are very widespread. Most of the liquid crystal displays produced use either the twisted nematic (see Figure 7.3) or the supertwisted nematic electrooptical effects.6 The liquid crystal materials used in these cells contain a chiral component (effectively a cholesteric phase) which determines the twisting direction. Cholesteric LCs can also be used for storage displays utilizing the dynamic scattering mode.7 Short-pitch cholesterics with temperature-dependent selective reflection in the visible region show different colors at different temperatures and are used for popular digital thermometers.8... 

It can be safely predicted that applications of liquid crystals will expand in the future to more and more sophisticated areas of electronics. Potential applications of ferroelectric liquid crystals (e.g. fast shutters, complex multiplexed displays) are particularly exciting. The only LC that can show ferroelectric property is the chiral smectic C. Viable ferroelectric displays have however not yet materialized. Antifer-roelectric phases may also have good potential in display applications. Supertwisted nematic displays of twist artgles of around 240° and materials with low viscosity which respond relatively fast, have found considerable application. Another development is the polymer dispersed liquid crystal display in which small nematic droplets ( 2 gm in diameter) are formed in a polymer matrix. Liquid crystalline elastomers with novel physical properties would have many applications. 

Certain aryl amines are endowed with unusual electronic properties. Schiff s bases such as 4-methoxybenzylidene-4-n-butylaniline were the original experimental chemicals used in the early development of electrical and electrooptical displays. Liquid crystal display (LCD) technology relies on twisted nematic or supertwisted nematic effects. Later nematogen development was based on cyanobiphenyls103. 

The twisted nematic (TN) and supertwisted nematic (STN) liquid crystals are widely used in liquid crystal displays. The former is used in wrist watches and calculators while the latter is used in notebook computers. 

The subject of liquid crystals has now grown to become an exciting interdisciplinary field of research with important practical applications. This book presents a systematic and self-contained treatment of the physics of the different types of thermotropic liquid crystals - the three classical types, nematic, cholesteric and smectic, composed of rod-shaped molecules, and the newly discovered discotic type composed of disc-shaped molecules. The coverage includes a description of the structures of these four main types and their polymorphic modifications, their thermodynamical, optical and mechanical properties and their behaviour under external fields. The basic principles underlying the major applications of liquid crystals in display technology (for example, the twisted and supertwisted nematic devices, the surface stabilized ferroelectric device, etc.) and in thermography are also discussed. 

Surface-stabilized ferroelectric liquid crystal Splay-twist Supertwisted nematic Transmission electron microscopy Twisted nematic Thin film transistor Uniform lying helix Ultraviolet... 

T. Scheffer and J. Nehring, Twisted nematic and supertwisted nematic mode LCDs, in Liquid crystals-applications and uses, Vol. 1, ed. B. Bahadur (World Scientific, New Jersy, 1990). 

This book was conceived as a renewed version of the earlier published original book, Electro-Optical and Magneto-Optical Properties of Liquid Crystals (Wiley, Chichester, 1983) written by one of us (L.M. Blinov). That book was first published in Russian (Nauka, Moscow, 1978) and then was modified slightly for the English translation. Since then new information on electrooptical effects in liquid crystals has been published. Novel effects have been discovered in nematics and cholesterics (such as the supertwist effect), and new classes of liquid crystalline materials, such as ferroelectric liquid crystals, appear. Recently, polymer liquid crystals attracted much attention and new electrooptical effects, both in pure polymer mesophases and polymer dispersed liquid crystals, were studied. An important contribution was also made in the understanding of surface properties and related phenomena (surface anchoring and bistability, flexoelectricity, etc.). 

The current (third) period, which may be called a colonization, involves wide electrooptical investigations of novel effects in ferroelectric liquid crystals [9, 10] and a study of exotic materials like polymeric and lyotropic mesophases, blue phases in cholesterics, well-ordered smectics, and so on. For conventional (nematic and cholesteric) phases the accent was shifted to the optimization of the material properties for electrooptical devices, though novel phenomena like the supertwist effect [11] and a gamma of linear electrooptical effects [12-14] have also been discovered. 

Liquid Crystal Materials for Twisted Nematic and Supertwisted Nematic... 

Besides normal alkyl chains, alkenyl chains (-C H2 CH CHCH3) are also important because they exhibit particularly beneficial elastic constants and low rotational viscosities desirable for use in supertwisted nematic (STN) displays. Branched alkyl chains Iowct transition temperatures and increase the viscosity. Thus, chiral liquid crystal compounds, which usually incorporate a branched chain alcohol, e.g., 2-methyl butanol or 2-octanol, are relatively viscous. Compounds with two long alkyl chains favor smectic C phase formation (3, K-S, 48°C S.-S 122°C S -N 128°C N-I 166°C), especially when the core system contains some kind of nonlinear stmcture (such as a lateral substituent and/or este group) which aids the formation of tilted phases. 

See, for example, Scheffer, X, and J. Nehring. 1993. Twisted nematic and supertwisted nematic mode LCDs. Liquid Crystals Applications and Uses, B. Bahadur (ed.), Singapore World Scientific. see also Kataoh, K., Y Endo, M. Akatsuka, M. Ohgawara, and K. Sawada. 1987. Apphcation of retardation compensation A new highly multiplexable black-white hquid crystal display with two supertwisted nematic layers. Jpn. J. Appl. Phys., Part 2 26 L1784. 

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