Foreword. Series Editor's Foreword. Preface. 1. Liquid crystal physics.* Introduction.* Thermodynamics and statistic physics.* Orientational order.* Elastic properties of liquid crystals.* Response of liquid crystals to electro-magnetic fields.* Anchoring effects of nematic liquid crystal at surfaces. 2. Propagation of light in anisotropic optical medium.* Electromagnetic wave.* Polarization.* Propagation of light in uniform anisotropic optical media.* Propagation of light in cholesteric liquid crystals. 3. Optical modeling methods.* Jones matrix method.* Mueller matrix method.* Berreman 4x4 method. 4. Effects of Electric field on Liquid Crystals.* Dielectric interaction.* Flexoelectric Effect.* Ferroelectricity in liquid crystals. 5. Freedericksz transition.* Calculus of variation.* The Fredeericksz transition: statics.* The Freedericksz transition: dynamics. 6. Liquid Crystal Materials.* Introduction.* Refractive indices.* Dielectric constants.* Rotational Viscosity.* Elastic constant.* Figure-of-merits.* Refractive index matching between liquid crystals and polymers. 7. Modeling of liquid crystal director configuration.* Electric energy of liquid crystals.* Modeling electric field.* Simulation of liquid crystal director configuration. 8. Transmissive liquid crystal display.* Introduction.* Twisted nematic cells.* In plane switching (IPS) mode.* Vertical alignment (VA) mode.* Multi-domain Vertical Alignment (MVA) Cells.* Optically compensated bend (OCB) cell. 9. Reflective and Trasreflective display.* Introduction.* Reflective liquid crystal displays.* Transflector.* Classification of Transflective LCDs.* Dual-cell-gap Transflective LCDs.* Single-cell-gap Transflective LCDs.* Performance of transflective LCDs. 10. Liquid crystal display matrices, drive schemes and bistable displays.* Segmented displays.* Passive matrix displays and drive scheme.* Active Matrix Displays.* Bistable ferroelectric liquid crystal displays and drive scheme.* Bistable nematic displays.* Bistable cholesteric reflective display. 11. Liquid crystal/polymer composites. * Introduction.* Phase separation.* Scattering properties of liquid crystal/polymer composites.* Polymer dispersed liquid crystals.* Polymer stabilization liquid crystals.* Displays from liquid crystal/polymer composites. 12. Tunable liquid crystal photonic devices. * Introduction.* Laser beam steering.* Variable Optical Attenuators.* Tunable-Focus Lens.* Polarization-Independent LC Devices. Index.

Fundamentals of Liquid Crystal Devices

This critical review begins with a brief, but essential, introduction to the special nature of liquid crystal materials, their peculiar properties, and their commercial applications, followed by an introductory insight into the remarkable nature of the fluoro substituent, and its fascinating influence on the properties of organic compounds. However, the main focus of the review is to discuss the enormous amount of exciting research on fluorinated liquid crystals that has been reported. The small size of the fluoro substituent enables its incorporation into all types of liquid crystal, including calamitic, discotic, banana, lyotropic, and polymers, without ruining the liquid crystalline nature of the material. However the fluoro substituent is larger than hydrogen, and hence causes a significant steric effect, which combined with the high polarity, confers many fascinating, and often remarkable, modifications to melting point, mesophase morphology and transition temperatures, and the many other very important physical properties, such as dielectric anisotropy, optical anisotropy, and visco-elastic properties. There are many different positions within a liquid crystal structure where a fluoro substituent can be located, including (i) a terminal position, (ii) within a terminal chain, as a semi-fluorinated or as a perfluorinated chain, or as one fluoro substituent at a chiral centre, (iii) as part of a linking group, and (iv) a lateral position in the core section. Such variety enables the interesting and advantageous tailoring of properties, both for the fundamental purposes of establishing structure–property relationships, and for materials targeted towards commercially-successful liquid crystal display applications.

Fluorinated liquid crystals – properties and applications

Substances forming calamitic mesophases have been known for more than 100 years but only the recent, rapid advance in active matrix liquid crystal display (AM-LCD) technology helped these materials to achieve the crucial position in flat panel display technology they hold today. Due to their high contrast, large viewing angle, and rapid switching times, modern AM-LCDs offer a superior picture quality even compared to conventional cathode ray tubes. Their flatness, low weight, and low energy consumption render them the technology of choice for all kinds of portable devices. Some of the future promises of AM-LCD technology are centered around the development of liquid crystalline materials for the different subtypes of active matrix applications. This development is aimed, on the one hand, towards improved electrooptical and viscoelastic properties; on the other hand, the increasing performance of LCDs leads to extremely stringent reliability demands on the liquid crystals. Responding to these high standards of performance and quality, most liquid crystals for contemporary AM-LCD applications are multiply fluorinated compounds with very high purities, as is typical for materials used in the electronics industry. The synthesis of these superfluorinated materials (SFMs) often requires specialized methods, which, in several cases, had to be introduced for the first time into the canon of industrial production. The immense market pressure, as well as the rapid advance of AM-LCD technology on the side of the display manufacturers, urges an increasing pace of the materials development. This demand for new materials can no longer be fulfilled by conventional trial-and-error approaches. As in the pharmaceutical industry, in the search for new, superior liquid crystals, the purely empirical methods are increasingly supported by a rational design based on computational methods.

Nematic Liquid Crystals for Active Matrix Displays: Molecular Design and Synthesis.

Liquid crystals, compounds and mixtures with positive dielectric anisotropies are reviewed. The mesogenic properties and physical chemical properties (viscosity, birefringence, refractive indices, dielectric anisotropy and elastic constants) of compounds being cyano, fluoro, isothiocyanato derivatives of biphenyl, terphenyl, quaterphenyl, tolane, phenyl tolane, phenyl ethynyl tolane, and biphenyl tolane are compared. The question of how to obtain liquid crystal with a broad range of nematic phases is discussed in detail. Influence of lateral substituent of different kinds of mesogenic and physicochemical properties is presented (demonstrated). Examples of mixtures with birefringence ∆n in the range of 0.2–0.5 are given.

High Birefringence Liquid Crystals

Substanzen, die calamitische Mesophasen bilden, kennt man schon seit mehr als 100 Jahren, doch erst der rasche Fortschritt in der Technik der Aktiv-Matrix-Flussigkristalldisplays (AM-LCDs) fuhrte dazu, dass sie ihre heutige Bedeutung in der Flachbildschirmtechnologie erlangen konnten. Auf Grund ihres hohen Kontrastes, des weiten Blickwinkels und der kurzen Schaltzeiten erreichen moderne AM-LCDs eine Bildqualitat, die haufig sogar der von konventionellen Kathodenstrahlrohren uberlegen ist. Geringer Platzbedarf, geringes Gewicht und geringer Energieverbrauch machen sie zur Technologie der Wahl fur viele tragbare elektronische Gerate. Einige der Zukunftsperspektiven der AM-LCD-Technologie konzentrieren sich auf die Entwicklung flussigkristalliner Substanzen fur die verschiedensten Aktiv-Matrix-Anwendungsbereiche. Zum einen zielt diese Entwicklung auf verbesserte elektrooptische und viskoelastische Eigenschaften ab, zum anderen fuhrt die zunehmende Leistungsfahigkeit der LCDs zu auserst strengen Anforderungen an die Qualitat der Materialien. Um diesen gerecht zu werden, sind die meisten Flussigkristalle fur AM-LCD-Anwendungen heutzutage mehrfach fluorierte Verbindungen von hohem Reinheitsgrad, wie er in der Elektronikindustrie typisch ist. Fur die Synthese dieser so genannten SFMs (superfluorinated materials) bedarf es oft spezieller Methoden, die in einigen Fallen erst auf den Masstab industrieller Produktion ubertragen werden mussten. Der ungeheure Marktdruck und der rasche Fortschritt in der AM-LCD-Technologie bei den Displayherstellern drangt geradezu auf ein schnelleres Tempo bei der Entwicklung dieser Substanzen. Dieser Forderung kann man mit dem konventionellen Vorgehen, das den Erfolg haufig dem Zufall uberlasst, nicht mehr gerecht werden. Wie in der pharmazeutischen Industrie werden bei der Suche nach neuen, besseren Flussigkristallen die rein empirischen Methoden vermehrt durch ein rationales Design auf der Grundlage von Rechenverfahren unterstutzt.

Nematische Flüssigkristalle für Aktiv‐Matrix‐Displays: Design und Synthese

Eight types of two- and three-ring liquid-crystalline compounds each possessing a 3,4-difluorophenyl substituent were synthesized. Their liquid-crystalline mixtures were such as to make them useful for active matrix displays, such as TFT (thin-film-transistor) and MIM (metal-insuiator-metal) systems. They have high stability and low viscosity, very important properties so far not possible with conventional substances.

S. Sugimori

Papers

Fluorinated Liquid Crystals for Active Matrix Displays