Colored twisted nematic cells

It should be mentioned that selective polarizers or retarding layers can also be applied to twisted nematic devices. Kabayashi [95] has shown that with twisted nematic cells in combination with different additional selective polarizers multicolor field effect devices with over 20 different colors are available. 

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... 

In the 1980s, the research and development of AM LCDs were very active, but it had not yet opened great application. On the other hand, STN-LCD (super twisted nematic LCDs) for PCs and Japanese word processors were realized in the 1980s [7], and also colored STN-LCDs for PCs were developed. The electro-optical response increased steeply with increasing applied voltage for those cells and enough contrast was provided even if the number of scanning lines increased, and... 

Table 4.1 summarizes which type of the LC film series is compatible for each LCD mode. Twisted oriented films can be used for color compensation of STN (super twisted nematic)-LCDs [36], in particular for color STN-LCDs in mobile devices. Because such color mobile STN-LCDs use only one polarizer, it is necessary that the combination of the compensation film and STN cell functions as a wideband A/4 plate. Multiple films are required in order to achieve this condition for usual, stretched films, but by using the twisted oriented film this can be realized by just one film [37-39]. 

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