Subject twisted nematic

The widespread use of the twisted nematic device as the display mode above an active matrix array has highlighted its shortcomings. Such displays, which command a significant price premium in the marketplace, are subject to increasing scrutiny over the quality of the image. The narrow and non-uniform viewing cone of the normal twisted nematic display is increasingly viewed as an unacceptable aspect of performance, and various approaches have been described that seek to provide a better solution [34]. 

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. 

A typical case of the nonmonotonic behavior of the pitch (in fact, the inversed pitch Pq ) on mixture composition is shown in Fig. 1.18 [45, 46]. It is worthwhile to note that all left-hand cholesterics (like cholesteryl acetate, pelargonate, and oleate) form left-hand mixtures with BBBA. On the other hand, for right-twisted cholesterics (like Ch, chloride) we can observe a change in the sign of the helix from left to right. There are also compensation points where a mixture is achiral. In this case, a nematic matrix itself, not being twisted initially behaves like a left-hand cholesteric. This problem was the subject of a hot theoretical discussion [47, 48]. 

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