Liquid crystal mixtures
AssigneeHoffmann-La Roche Inc.
InventorsArthur Boller, Alfred Germann, Martin Schadt, Hanspeter Scherrer
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Abstract
Liquid crystal mixtures having positive anisotropy of the dielectric constants comprising a nematogenic material having a clearing point above 60.degree. C., one or more compounds of the formula ##STR1## wherein R.sub.1 and R.sub.2 are hydrogen or straight-chain alkyl, provided that at least one of R.sub.1 and R.sub.2 is other than hydrogen and that R.sub.1 and R.sub.2 together contain no more than 9 carbon atoms, and, if desired, one or more additional doping agents, are described.
Claims15
A nematic liquid crystal mixture having positive anisotropy of the dielectric constants comprising a nematogenic material having a clearing point above 60.degree. C. and one or more compounds of the formula ##STR18## wherein R.sub.1 and R.sub.2 are hydrogen or straight-chain alkyl, provided that at least one of R.sub.1 and R.sub.2 is other than hydrogen and that the sum of the number of carbon atoms present in R.sub.1 and R.sub.2 is at most 9.
An electro-optical apparatus comprising a nematic liquid crystal mixture having positive anisotropy of the dielectric constants comprising a nematogenic material having a clearing point above 60.degree. C. and one or more compounds of the formula ##STR31## wherein R.sub.1 and R.sub.2 are hydrogen or straight-chain alkyl, provided that at least one of R.sub.1 and R.sub.2 is other than hydrogen and that the sum of the number of carbon atoms present in R.sub.1 and R.sub.2 is at most 9,
- disposed between two plate means at least one of which plate means is transparent;
- means for controlling the optical activity of the cell;
- and said liquid crystal means having a helical structure in the direction perpendicular to the plate means and the surfaces of the plate means being wall oriented.
A rotation cell comprising a nematic liquid crystal mixture having positive anisotropy of the dielectric constants comprising a nematogenic material having a clearing point above 60.degree. C. and one or more compounds of the formula ##STR32## wherein R.sub.1 and R.sub.2 are hydrogen or straight-chain alkyl, provided that at least one of R.sub.1 and R.sub.2 is other than hydrogen and that the sum of the number of carbon atoms present in R.sub.1 and R.sub.2 is at most 9,
- disposed between two plate means at least one of which plate means is transparent;
- means for controlling the optical activity of the cell;
- and said liquid crystal means having a helical structure in the direction perpendicular to the plate means and the surfaces of the plate means being wall oriented.
Dependencies are inferred from the claim text.