We present a new bistable scattering effect in a filled nematic liquid crystal, and its application to a high resolution laser-addressed display. The filled nematic consists of a small fraction of inorganic particles of nm size in a nematic liquid crystal with positive dielectric anisotropy. The scattering ON state is reached by locally writing with a laser. The transparent OFF state can be obtained by combining a moderate voltage with selective application of the laser to the part to be erased. The key parameters controlling the processes and the possible physical mechanisms involved are discussed.
We have found that 4-[trans-4-alkylcyclohexyl]benzoni-triles ( 4 ) form nematic phases with higher clearing points and wider temperature intervals than those of the industrially important 4-alkylbiphenyl-4-carbonitrilesrt1. This means that the effect of a short-range orderr2] of steric origin on the stability of nematic phases must be much greater than hitherto assumed. H -1 J. R Compounds ( 4 a ) to ( 4 e ) (Table 1) are obtained as follows:The cisltrans isomeric 4-alkyl-1 -phenylcyclohexanols (2) and (2') formed in approximately equal amounts on reaction of 4-alkylcyclohexanone (I) with phenylmagnesium bromide in diethyl ether are separated on a column packed with silica gel (Kieselgel 60, Merck). Light petroleum (boiling range 50 to 70°C) containing an amount of diethyl ether increasing up to 15 vol-"/;:, was used as solvent. (2) is hydrogenated with retention over Raney nickel in ethanol, and (2') with inversion over palladium/activated charcoal (10 % Pd) in ethanol. The nitrile group is introduced into the common product (3) in known manner (Friedel-Crafts acetylation, haloform reaction to give the carboxylic acid, conversion into the amide, and dehydration with P0Cl3).The structures of the products ( 4 a ) to ( 4 e ) are in accord with the results ofelemental analysis and the IR and I3C-NMR spectra. Since the formation of a nematic phase requires an elongated molecular shapeL31, compound ( 4 ) probably exists in the equatorial trans form. Table I . Properties of compounds (4). R Yield [a] M.p. Clearing ["/.I YC] point I"CJ[a] Based on amount of ( 1 ) weighed in.[b] (4e) has a smectic-nematic transition at 17°CCompounds ( 4 ) have viscosities of about 20 CP at 20°C. These low values are advantageous for their application in electro-optical devices. The absorption maxima at 235 nm suggest use of eutectic mixtures as solvents in the study of anisotropic molecular properties. The optical anisotropy lies between 0.12 and 0.13, and the D C anisotropy is around + 10. We report here on a new method, extensively tested by us['', for the assignment of the configuration of di-and trialkyl-substituted olefins, diols, and epoxides, as well as for
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