Owain Llyr Parri

Liquid Crystals with a Thiomethyl End Group: Lateral Fluoro Substituted 4-(trans-4-(n-Propyl) Cyclohexylethyl-4′-Thiomethylbiphenyls and 4-n-Alkyl-4″-Thiomethylterphenyls

Abstract The synthesis and mesogenic properties of some lateral fluoro substituted 4-(trans-4-(n-propyl)cyclohexylethyl)-4′-thiomethylbiphenyls and 4-n-alkyl-4″-thiomethylterphenyls are described. Birefringence (Δn) and dielectric anisotropy (Δϵ) measurements for these compounds are also given and compared with analogous terminal chloro, cyano and methoxy compounds. It is found that the use of a terminal thiomethyl group produces compounds of intermediate Δn, Δϵ and clearing point than analogous terminal chloro, methoxy and cyano compounds. The terminal thiomethyl group is also more smectogenic than any of the other three terminal endgroups. In most cases, however, the melting points of the compounds are too high to be of practical use.

Patterned retarder films using reactive mesogen technology

A range of polymerisable liquid crystals mixtures have been developed (so called, Reactive Mesogen) that are ideally suited for the fabrication of patterned retarder films. Such films, made using a combination of Merck Reactive Mesogen Mixtures coated on a plastic substrate containing a photoalignment layer, are commercially employed to produce 3D displays. Different methods of patterning Reactive Mesogen Mixtures are discussed and the merits of each considered. Although the first commercial products use normal dispersion Reactive Mesogen Materials, the advantages of using the next generation of materials, which have improved wavelength dispersion, are introduced with a focus on their use in 3D patterned retarder films.

Reactive liquid crystal materials for optically anisotropic patterned retarders

Merck has developed a range of reactive liquid crystal materials (Reactive Mesogens) that are designed to form thin, birefringent, coatable films for optical applications. Reactive Mesogen (RM) films are typically coated from solution and polymerized in-situ to form thin, optics-grade coatings. Merck RM materials are customized formulations including reactive liquid crystals, surfactants, photoinitiators and other proprietary additives. Merck have optimized the materials to achieve the optimum physical performance in each application. In this paper we focus on the optimization of RM materials to achieve the finest patterning resolution and defined feature shape whilst maintaining good physical properties of the films. Several conventional trade-offs are investigated and circumvented using novel material concepts. Different methods of patterning RM materials are discussed and the merits of each considered. Thermal annealing of non-polymerized regions can create isotropic islands within the polymerized anisotropic matrix. Alternatively, the non polymerized material can be re-dissolved in the coating solvent and rinsed away. Each of these techniques has benefits depending on the processing conditions and these are discussed in depth.

Advances in LC display performance using optical films

New generations of large area liquid crystal displays require very high optical performance to compete with CRT and other emerging technologies. This performance must include high contrast ratio, high stability of all grey levels, and excellent colour reproduction, and typically this is requested for up to 80# viewing angles in all directions. Some potential difficulties to achieving wide viewing performance in single domain LCDs are discussed, with explanation for the advantages to multi-domain LC display. Finally we shall describe some new optical film developments which can be used to achieve the targets for high performance at all viewing angles combining multi-domain LC display, together with optical films prepared from reactive mesogens.

Plasma‐beam alignment of passive liquid crystals (Invited Paper)

— A plasma-beam process, developed for the alignment of liquid crystals (LC) in electro-optic applications, has been successfully applied to align “non-standard” LC, such as crystalline materials with LC phases at elevated temperatures and reactive mesogenes. In addition to the high alignment quality of the materials, there is no need for an intermediate layer between the substrate and the LC layer. Furthermore, the construction of our source simplifies the alignment procedure of large-area rigid substrates and the roll-to-roll processing of flexible films. This method opens new horizons for optical retarders and polarizers, as well as anisotropic semiconducting films for organic electronics.

Biaxial integrated optical film for VA mode LCD's made from in‐situ photopolymerised reactive mesogens

Abstract For high end, large area displays, all current LC modes require some degree of optical compensation to improve the front of screen viewing experience. Currently most optical films are laminated to the outside of the LCD cell, between the glass and polariser. In this paper we wish to show how it is possible to integrate the compensating optical film within a VA mode LCD cell. The paper will describe the process of making the biaxial film through the process of in‐situ photopolymerisation of an aligned film of reactive mesogens in the cholesteric phase using polarised UV light. The film can be made on the colour filter array side of the LCD panel. In addition the process of fabricating a VA mode LCD containing this film will be described and the performance of this module will be presented.

Unusual Odd-Even Effects in Vinyl Ether and Acrylated Direactive Liquid Crystals

Abstract Four series of direactive liquid crystals are presented and their physical properties characterised. The core groups are based on either a lateral chloro or methyl terphenyl and the reactive groups are either acrylates or vinyl ethers. It is shown that reactive liquid crystals with vinyl ether reactive groups have higher transition temperatures, birefringence, and order parameter than the corresponding acrylates. Both the vinyl ether and acrylate series show an odd-even effect in transition temperatures, birefringence and order parameters. The odd-even effect in the vinyl ether series is particularly marked.