Liquid-crystalline mixtures, in particular ferroelectric liquid-

Details Liquid-crystalline mixtures, in particular ferroelectric liquid- Liquid-crystalline mixtures, in particular ferroelectric liquid-

1991-11-06

1994-02-15

Stoll, Robert L.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229967, C09K 1934, C09K 1920

Patent

active

052864090

DESCRIPTION:

BRIEF SUMMARY
Ferroelectric liquid crystals have recently attracted interest as a display medium in electrooptical assemblies (for example Lagerwall et al., "Ferroelectric Liquid Crystals for Displays", SID Symposium, October Meeting 1985, San Diego, Calif. USA).
For practical use of ferroelectric liquid crystals in electrooptical displays, chiral, tilted, smectic phases, such as S.sub.c phases, are required (R. B. Meyer, L. Liebert, L. Strzelecki and P. Keller, J. Physique 36, L-69 (1975).vertline., which are stable over a broad temperature range. This aim can be achieved by means of compounds which themselves form such phases, for example S.sub.c phases, or, however, by doping compounds which form non-chiral, tilted, smectic phases, with optically active compounds (M. Brunet, C. Williams, Ann. Phys. 3, 237 (1978).vertline..
Furthermore, a unitary planar orientation of the liquid crystals is necessary in order to achieve a high contrast ratio when ferroelectric liquid-crystal mixtures are used in electrooptical assemblies. It has been shown that a unitary planar orientation in the S.sub.c phase can be achieved if the phase sequence of the liquid-crystal mixture with decreasing temperature is as follows:
Isotropic T nematic T smectic A T smectic C.
(for example K. Flatischler et al., Mol. Cryst. Liq. Cryst. 131, 21 (1985); T. Matsumoto et al., p. 468-470, Proc. of the 6th Int. Display Research Conf., Japan Display, 30 Sep. - 2 Oct. 1986, Tokyo, Japan; M. Murakami et al., ibid., p. 344-347).
For ferroelectric (chiral smectic) liquid-crystal mixtures, the condition that the pitch of the helix must be large, i.e. greater than 5 .mu.m, in the S.sub.c * phase and must be very large, i.e. greater than 10 .mu.m or infinite, in the N* phase must additionally be fulfilled.
The optical switching time .tau[mu.s] of ferroelectric liquid-crystal systems, which should be as short as possible, depends on the rotation viscosity of the system .gamma.[mPas], the spontaneous polarization P.sub.s [nC/cm.sup.2 ] and the electric field strength E[V/m], in accordance with the equation ##EQU1## Since the field strength E is determined by the electrode separation in the electrooptical assembly and by the applied voltage, the ferroelectric display medium must have low viscosity and high spontaneous polarization in order that a short switching time is achieved.
Finally, besides thermal, chemical and photochemical stability, a small optical anisotropy .DELTA.n, preferably <0.13, and a small positive or, preferably, negative dielectric anisotropy .DELTA..epsilon. are required. (S. T. Lagerwall et al., "Ferroelectric Liquid Crystals for Displays" SID Symposium, Oct. Meeting 1985, San Diego, Calif., USA).
It is only possible to satisfy all these demands using mixtures comprising several components. The basis (or matrix) used here is preferably compounds which if possible themselves already have the desired phase sequence I.fwdarw.N.fwdarw.S.sub.1 .fwdarw.S.sub.c. Further components of the mixture are often added to reduce the melting point and to broaden the S.sub.c and usually also the N phase, to induce optical activity, for pitch compensation and to match the optical and dielectric anisotropy; however, the rotation viscosity, for example, should if possible not be increased at the same time.
It is known that certain derivatives of phenylpyrimidine, in particular 5-alkyl-2(4-alkoxyphenyl)pyrimidines, are capable of forming S.sub.c, S.sub.A and N phases (D. Demus and H. Zaschke, "Flussige Kristalle in Tabellen", [Liquid Crystals in Tables], VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig 1974, pp. 260-261) and, in addition, can be converted into ferroelectric liquid-crystal mixtures by addition of optically active dopes [L. M. Blinov et al., Sow. Phys. lisp. 27 (7), 492 (1984); L. A. Beresnew et al., Ferroelectrics, 59 (321]/1 (1984), presented at the 5th Conference of Soc. Countries on Liquid Crystals, Odessa, USSR, Oct. 1983; DE-A-3,515,347, EP-A 0,206,228 and EP-A 0,225,195].
It is furthermore known that lower melting points and a broade

REFERENCES:
patent: 4855429 (1989-08-01), Heppke et al.
patent: 5064566 (1991-11-01), Hopf et al.
patent: 5071589 (1991-12-01), Dubal et al.

Affiliated with

Also associated with

Rating

Liquid-crystalline mixtures, in particular ferroelectric liquid- does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Liquid-crystalline mixtures, in particular ferroelectric liquid-, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid-crystalline mixtures, in particular ferroelectric liquid- will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1204487