Thomson-csf

Annie Zann

Jean-Claude Dubois

Alain Beguin

Jean Claude Dubois

Jean P Billard

Huu Tinh Nguyen

Michel Hareng

Maryse Gazard

Andre Couttet

Jean Claude Lavenu

Tinh H Nguyen

Marie A Abert-Mellah

Cholesteric liquid crystals of the so-called reentrant mesogenic type obtained by mixing a substance such as a cholesterol ester having molecules of the 'chiral' type with a liquid crystal of the so-called reentrant nematic type such as a substance corresponding to the general formula: ##STR1## where R is an alkyl or alkoxy or alkylcarbonate group with:

Cholesteric liquid crystal of the reentrant type and a

A family of liquid crystals having a type A smectic mesophase with a positive dielectric anisotropy, which are particularly useful in the case of the thermo-optical effect. The substances of the family are in accordance with the general formula: ##STR1## in which R represents an organic group of the alkyl or alkoxy type containing 1 to 15 carbon atoms and in which X and Y designate either the bromine or the nitrile radical.

Type A smectic liquid crystal having a positive dielectric anisotropy

A mixture of liquid crystals having a mesophase of the disc-like with wires-type, where a sensitivity to the electrical field can be observed and application can be made to visual display cells. The mixture comprises two hexasubstituted triphenylene derivatives, to the nucleus of which are fixed six identical radicals in positions 2, 3, 6, 7, 10 and 11, which can be alkyl, alkoxy, alkylcarboxylate, alkylbenzoate, and alkoxybenzoate radicals. The electro-optical devices can either be of the variable birefringence type when the liquid crystal molecules have their optical axes parallel to one another and to the walls of a display cell, or of the type with a variable rotatory power under the action of an electrical field when a helical type arrangement is used, or finally, under the effect of a relatively strong field, of the type with dynamic light diffusion.

Mixture of disc-like liquid crystals, electro-optical device using such

The invention concerns a substance of diester type, i.e. an organic compound with three benzene nuclei joined by --COO-- groups, exhibiting at least one mesomorphic phase of smectic type. The substance of the invention answers to the formula: ##STR1## where R.sub.1 is an alkyl or alkoxy radical and R.sub.2 an alkyl. In the case where R.sub.1 is an octyl and R.sub.2 a pentyl there is a dielectric isotropy frequency of 30 kHz, i.e. a frequency where the dielectric anistropy changes sign. Application to field-effect display devices with dual-frequency memory.

Liquid crystal of diester type exhibiting a smectic phase, with low

The invention relates to an organic compound having an enantiotropic or monotropic mesomorphous phase. The compound according to the invention complies with the general chemical formula: ##STR1## in which R is an alkyl radical, R' another alkyl radical or an alkoxy radical and the symbol  is a radical which can either be an aromatic nucleus or a radical with two aromatic nuclei or a cyclohexane radical or contain at least one cyclohexane radical or a heterocycle of type ##STR2##

Mesomorphous 4-alkoxytetrafluorobenzoic acid esters

A family of diphenylic esters are disclosed, which, within certain temperature ranges exhibit mesomorphic phases, either smectic or nematic, having the general formula: ##STR1## where R.sub.1 is C.sub.n H.sub.2n+1 O or C.sub.n H.sub.2n+1 in which n is an integer of from 1 to 10,

Diphenylic esters exhibiting mesomorphic phases

A family of organic compounds having at least one mesomorphic phase of nematic type and, in respect of some compounds, one or more smetic phases. The liquid crystals according to the invention satisfy general formula: ##STR1## in which R.sub.1 is an alkyl or alkoxy group having n carbon atoms (n being an integer of 1 to 10) X designates the bromine or the cyano group, Y is a methyl group.

Family of liquid crystals of the disubstitute diester type

Novel mesomorphic substances, constituting, in certain temperature ranges, nematic or smectic liquid crystals which are compounds of the formula: ##STR1## wherein R.sub.1 is an alkoxy group containing 1 to 10 atoms of carbon;

Liquid crystal materials containing a diphenylethane nucleus

Novel mesomorphic substances, constituting, in certain temperature ranges, nematic or smectic liquid crystals which are compounds of the formula: ##STR1## wherein R.sub.1 is an alkyl or alkoxy group containing 1 to 10 atoms of carbon;

Liquid crystal materials having a formula containing a diphenylethane

A liquid crystal composition with high negative dielectric anisotropy, which is capable of exhibiting a high dynamic light scattering effect and of inducing similar characteristics into mixtures of the liquid crystal and another nematic liquid crystal and which derives an advantage from a larger mesomorphic temperature range, which comprises at least one compound of the formula: ##STR1## wherein R represents NO.sub.2, bromine or cyano; R.sub.1 is an alkyl or alkoxy group and R.sub.2 is an alkyl group.

Liquid crystal with high negative dielectric anisotropy and mixtures of

Novel mesomorphic substances, constituting, in certain temperature ranges, nematic or smectic liquid crystals, are compounds of the formula ##STR1## wherein Y is H or CN;

Liquid crystals with improved properties and devices using such liquid

An organic compound having a high negative dielectric anisotropy is capable, by mixing with a nematic liquid crystal, of improving the dynamic scattering effect of the liquid crystal. The organic compounds have the formula: ##STR1## in which R is either a fluoro or a nitrile radical and wherein R.sub.1 and R.sub.2 are alkyl radicals. An excellent dynamic scattering effect is obtained by mixing the new organic compound even in a low proportion with a nematic liquid crystal.

Alkylphenyl 3-cyano or fluoro-4-alkyloxybenzoates and mesomorphic

A nematic liquid crystal device for electro-optical display devices, is provided. Its long-shaped molecules are orientated perpendicularly to the electrode plates delimiting the crystalline liquid, i.e. homeotropically aligned. A polymer layer with long-chain molecules has been previously formed on the internal faces of each plate separately arranged on a discharge electrode of an electrical apparatus operating at high frequency (13.56 mc/s) and containing a vapour at very low pressure of a monomer such as hexamethyldisiloxane. The molecules of polymer thus formed are perpendicular to the plates and a similar orientation of the liquid crystal molecules result from that, i.e. a homeotropic alignment.

Nematic liquid crystal of homeotropically aligned type and a method of

A mixture of liquid crystals comprising a substance which imparts a medium positive dielectric anisotropy, and substances which widen the mesomorphic temperature range or impart good long-term stability, is provided. The mixture in accordance with the invention comprises at least one substance of the formula: ##SPC1## Or its isomer of the formula: ##SPC2## Where R is an alkyl or alkoxy radical and at least one substance of the formula: ##SPC3## Where the radical R is of the same kind as mentioned earlier or substance of the formula: ##SPC4## Or its isomer of the formula: ##SPC5## Where R is an alkoxy radical.

Mixture of liquid crystals exhibiting positive dielectric anisotropy and

A nematic liquid crystal of high stability, which can be utilized at normal temperatures, is obtained from compounds of the formula ##SPC1## Wherein R is an alkyl group having 1 to 14 carbon atoms, which present at least one nematic phase in the supper cooled liquid state. As a second embodiment, mixtures of the above compound with other nematic compounds formed nematic structures over wide temperature ranges.

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Paris, France

Annie Zann