Smectic liquid crystal high-contrast control or display device

1. A liquid-crystal switching or display device comprising a chiral smectic liquid-crystal mixture in monostable alignment, characterized in that the ratio Δ/Θ of the angle between the rubbing direction and the smectic layer normal to the tilt angle in the liquid-crystal mixture is at least 0.41.

2. A liquid-crystal switching or display device as claimed in claim 1 , characterized in that the liquid-crystal mixture has the phase sequence I-N-C and the tilt angle Θ at 25° C. is between 19° and 39°.

3. A liquid-crystal switching or display device as claimed in claim 1 , characterized in that the mixture has a spontaneous polarization of less than 150 nC/cm 2 .

4. A liquid-crystal switching or display device as claimed in claim 1 , characterized in that the device is an active-matrix or passive-matrix display.

5. A liquid-crystal switching or display device as claimed in claim 1 , wherein the chiral smectic liquid-crystal mixture has the following properties:

phase sequence I-N-C and

Tc is greater than 50° C. and

wherein T NI is phase transition temperature from the nematic to the isotropic phase less than 105° C. and

19°<tilt angle (25° C.)<390 and

spontaneous polarization less than 150 nC/cm 2 and

pitch of the cholesteric helix greater than 2 μm and

the difference of the tilt angles measured at 15° C. and 5° C. below Tc, the upper limit of

the range of existence of the optically active smectic phase, is less than 9.5°.

6. The device as claimed in claim 5 , characterized in that the chiral smectic liquid crystal mixture comprises of nitrogen- or sulfur-containing heterocyclic compounds in an amount which is at least 20% by weight of total said mixture.

7. The device as claimed in claim 6 , characterized in that the chiral smectic liquid crystal mixture comprises at least one sulfur-containing heterocyclic compound which is a thiophene derivative.