Optimization of liquid crystals for television

Abstract

Abstract— LCD TVs have dramatically improved in performance during the last 2 years. At the same time, the sale prices decreased by more than 50%. Together with the introduction of digital terrestrial broadcasting, this resulted in increasing sales of LCD TVs. This paper gives an overview of the main liquid‐crystal display (LCD) technologies used for TVs. We discuss key materials, synthesis, structural property relationships, and the optimization of LC mixture properties. For all technologies, we have achieved fast‐switching LC mixtures (16 msec). Novel materials for LC mixtures for the next generation of superior performance LCD TVs with 8‐msec switching times are shown.

Design and Synthesis of Chiral Nematic Liquid Crystals

“…• Does the LC mixture have the appropriate dielectric anisotropy ( ε; positive ε means the dipole moment acts along the long molecular axis) to ensure that it 14.3 Applications of Chiral Nematic Phases 5 couples with an applied electric field to effect full switching. This would usually be controlled by addition of a component that contains a strong dipole-containing group (e.g., CN, F, or CF 3 ) at a particular location in the structure [27]. • Color purity of the chiral nematic phase -does the effective birefringence ( n) of a mixture need to be tailored to suite a specific range?…”

“…These low temperature restrictions were countered to some extent by the incorporation of either a further phenyl ring or by a -CH 2 -CH 2 -link between the existing rings, to give chiral terphenyl or phenylethylbiphenyl based structures [121]. In the case of the chiral terphenyl (S)-(+)-4-(4-methylhexyl)-4 -cyano-p-terphenyl (27), the clearing point of the chiral nematic phase was raised to 186 • C; however, the material had a very high melting point of 120 • C, which again, not surprisingly, restricted its use. The use of the -CH 2 -CH 2 -link was much more successful in giving a compound with lower melting and clearing points; for example, (S)-(+)-1-[4 -(2-methylbutyl)biphenyl-4-y1]-2-(4-cyanophenyl)ethane (28).…”

VAN LCOS Microdisplays: A Decade of Technological Evolution

“…In the case of VAN, with its negative anisotropy, this results in a balancing exercise between the opposing needs for polar groups placed sideways of the main molecule chain to obtain the negative birefringence while at the same time minimizing the hindrance caused by these protruding fragments to facilitate the rotation of the molecules [11]. This is achieved by fundamental research into suitable chemical compounds [12], [13], resulting in new mixture formulations. Another possibility is to add a dopant to existing liquid crystal mixtures in order to change their hydrodynamic properties without altering the birefringent and dielectric properties.…”

“…Mixtures with higher birefringence while maintaining or slightly reducing the rotational viscosity have been developed mainly for the flat-panel TV application [13]. For microdisplays intended for projection, an additional constraint has to be taken into account.…”

Mesomorphic, dielectric, and optical properties of fluorosubstituted biphenyls, terphenyls, and quaterphenyls

“…The important properties of LC materials, required for electro-optical devices working in VA mode, are a nematic phase in a broad temperature range (from -40 to 110°C), medium birefringence Dn~0.1-0.2), negative dielectric anisotropy (De~-5), low rotational viscosity (g 1 < 100 Pa × s), high thermostability and photostability [1][2][3].…”