Twisted transitions, displays

This paper presents the numerical calculation of the influence of several device and material parameters on the shape of the optical transition/voltage curve of a twisted nematic display. 

The Freedericksz transition is also the basis of operation for most liquid crystal displays. In a twisted-nematic display cell, the surface anchoring at the two substrates is incommensurate, inducing a twist to the director field that rotates light polarization. Application of an electric field sufficiently strong to align the director... 

We first discuss the classical Freedericksz transitions and critical thresholds for a nematic. The understanding of these phenomena is crucial to the basic traditional idea of switching liquid crystal cells by fields having magnitudes above the critical threshold. The commercial exploitation of these results in liquid crystal display devices, especially the twisted nematic display to be discussed in Section 3.7 below, has greatly increased the general interest in theoretical and experimental aspects of Freedericksz transitions, and vice-versa. 

The body of evidence summarized within the aforementioned reviews clearly indicates that simple 1,2-dioxetanes decompose thermally through a twisted diradical-like transition state to afford predominantly a triplet-excited carbonyl with no direct emission of light (Scheme 1), while dioxetanes bearing an aromatic electron-donor moiety display intramolecular charge-transfer-induced decomposition with accompanying effective emission of light (Scheme 2). 

The first successful commercial liquid crystal display (LCD) was the twisted nematic (TN), still widely used in watches and calculators. A TN display is sketched in Fig. 5.24. It relies on the Freedericksz transition described in the preceding section. The cell consists of two glass plates coated with rubbed polyimide to induce orientation of the director parallel to the surface. In addition, there is a thin layer of the transparent conducting material, indium tin oxide. This is used to apply an electric field across the liquid crystal... 

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