Cholesteric LCD

FIGURE 8.46 Structure of the reflective bistable cholesteric LCD fabricated with a black PPy film as the electrode and the light absorbing layer. Relative reflectance as a function of applied AC voltage for the (a) chiral nematic mixture (CNM) and (b) CPD cells initially in either the planar (open symbols) or focal conic (filled symbols) state. Reflectance at 510 and 560 nm for the CNM and CPD cells, respectively, was measured after 200 Hz-AC field was applied for 20 ms and then removed. (From Kim, Y.C., et al.. Mol. Cryst. Liq. Cryst, 327,157,1999. With permission.)... 

Reduction potential, 13-2, 13-19 Reductive elimination, 9-8, 9-10-9-11, 9-21 Reflectance spectra, 15-25-15-26, 15-66-15-67 Reflective cholesteric LCD, 8-42-8-43 Reflective devices,... 

Figure 9.10 Schematic configuration of reflection type transflective cholesteric LCD and its operating principles at (a) voltage-off state, and (b) voltage-on state. Zhu 2006. Reproduced with permission from IEEE.

Y. P. Huang, X. Zhu, H. Ren, etal.. Full-color transflective cholesteric LCD with image-enhanced reflector, J. SID 12, 417 (2004). 

D. Davis, A. Kahn, X.-Y. Huang, and J. W. Doane, Eight-color high-resolution reflective cholesteric LCDs,... 

I. Shiyanovskaya, S. Green, G. Magyar, and J. W. Doane, Single substrate encapsulated cholesteric LCDs coatable, drapable and foldable, SID Inti Symp. Digest Tech. Papers, 36, 1556-1559 (2005). 

Figure 12.40. Data recorded from an integrated RGB stack of cholesteric LCDs, showing the spectral power distribution (left) and the corresponding chromaticity coordinates (right) (courtesy of J.W. Doane).

G.M. Podojil, D.J. Davis, X.-Y. Huang, N. Miller, and J.W. Doane, Plastic VGA reflective cholesteric LCDs with dynamic drive, SID Digest 98, 51 54 (1998). 

X.-D. Mi and D.-K. Yang, Cell designs for fast reflective cholesteric LCDs, SID... 

Licjuid Crystals. Ferroelectric Hquid crystals have been appHed to LCD (Uquid crystal display) because of their quick response (239). Ferroelectric Hquid crystals have chiral components in their molecules, some of which are derived from amino acids (240). Concentrated solutions (10—30%) of a-helix poly(amino acid)s show a lyotropic cholesteric Hquid crystalline phase, and poly(glutamic acid ester) films display a thermotropic phase (241). Their practical appHcations have not been deterrnined. 

Fig. I. Schematic diagrams of the contrast versus the applied field for (a) a twisted nematic, (b) a cholesteric guest-host bistable display (Wysocki ei al., 1972 Ohtsuka and Sukamoto, 1973), and (c) a bistable LCD (Boyd et al., 1982).

Figure 3.3 Schematic representation of a cholesteric-nematic phase-change effect (CNPC) LCD. ...

We consider only conventional LCDs that use nematic liquid crystals as the electrooptic material. There are less common types of LCDs that use other types of liquid crystals, such as cholesteric and ferroelectric liquid crystals. 

I. Dozov, A. Boissier and T. Laboureau, Nemoptic s bistable nematic liquid-crystal technology - Cholesterics or ferroelectrics are not necessary to make a bistable LCD, and using conventional nematics offers some substantial advantages, Information Display 18(1), 10 13, (2002). 

Tilt varies throughout the cell thickness In twisted cells due to a competition between the splay and bend elastic energies and the twist elastic energy. For small tilts and twists, 90 , this variation Is calculated to be small. Doping the liquid crystal with a cholesteric compound, as Is commonly done In TN-LCDs, stabilizes the twisted structure, thereby decreasing tilt variation. 

As the baseline for our calculations described in the Appendix, we take the typical LCD cell configuration of thickness d=8 ym filled with E7 liquid crystal mixture with a cholesteric additive giving a natural cholesteric pitch P=40 ym. The boundary conditions imposed on the liquid crystal are total twist 0q=9O , pretilt ao=3 and strong surface anchoring. The polarizers are crossed and parallel to the nematic director at the neighboring liquid crystal surfaces. In calculations where the total twist... 

The addition of cholesteric compound can be beneficial as it decreases the height of the bump in the transmission versus voltage curves at off normal incidence (see Fig. 2). The explanation of this effect is beyond the scope of this paper, however, it follows logically from a new model for operation of TN-LCDs reported elsewhere. 

Polymer-dispersed LC (PDLC) [30], polymer-stabilized cholesteric texture (PSCT) [31], and LC gels [32] all exhibit optical scattering characteristics and have wide applications in displays and optical devices. The LC gel-based reflective LCD can also be extended to transflective... 

To avoid the occurrence of domains with reverse tilt and domains with reverse twist in a TN-LCD, the use of an alignment layer with a pretilt angle more than about 5° and the addition of cholesteric dopants to the nematic liquid crystal mixture are preferable (see Section 2.1.1). 

---