Abstract: A liquid crystal display wherein in order to obtain an improved contrast without diminishing the brightness of the display, the angle of twist is reduced in the case of a liquid crystal display according to the rotating cell principle, polarizers with greater extinction power are used and up to 3% by weight of a suitable dye is added. Thus, a largely achromatic display is also obtained.

Abstract: In a matrix display device having a cholesteric liquid crystal the bistability effect is used which some cholesteric liquid crystals show. The liquid crystal shows a frequency-dependent relaxation of a positive to a negative dielectric anisotropy. After writing the information the light-scattering picture elements have a focal-conical texture and the transparent elements have a homeotropic-nematic texture. The information can be stored for a longer period of time by causing the homeotropic-nematic texture of the transparent elements to change into the substantially transparent planar-conical texture. This is produced rapidly by applying across all picture elements a voltage of a frequency at which the liquid crystal has a negative dielectric anisotropy. The focal-conical texture of the light-scattering elements is substantially not disturbed by this voltage. During the presence of this voltage the written information is continuously visible.

Abstract: In a liquid crystal display device which upon controlling with direct voltage shows a memory effect that can be erased by alternating voltage, the written area can expand beyond the edge of the electrode so that edge zones can no longer be erased readily. This disadvantage is avoided by covering the edges of the electrodes with an insulating layer.

Abstract: In a liquid crystal matrix display device in which the bistability effect of a cholesteric liquid crystal is used, the number of lines to be driven is increased by providing the electrodes (5) on grooves (3) provided in the supporting plates (1,2). The electrodes (5) partly overlap the part of a supporting plate present between two grooves. The electrode surface and the remaining surface of the supporting plates are covered by a dielectric layer (7). The grooves have a depth which is equal to half the desired thickness of the liquid crystal layer. Herewith a uniform thickness of the liquid crystal layer is also obtained.

Abstract: Nematic liquid crystalline mixtures of .alpha.-cyanostilbenes with negative electric anisotropy which are nematic liquid crystalline in a temperature range around room temperature. The mixtures contain the compounds 2-(p-ethoxyphenyl)-3-(p-hexyloxyphenyl)-acrylonitrile and 2-(p-butoxyphenyl)-3-(p-heptylphenyl)-acrylonitrile or the compounds 2-(p-butoxyphenyl)-3-(p-pentyloxyphenyl)-acrylonitrile and 2-(p-methoxyphenyl)-3-(pentylphenyl)acrylonitrile and are very suitable for practical application in picture display devices.