Liquid crystal materials, mixtures and devices

Details Liquid crystal materials, mixtures and devices Liquid crystal materials, mixtures and devices

1996-01-24

1999-01-19

Wu, Shean C.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229901, 25229961, 25229963, 25229964, 25229966, 25229967, 544303, 544334, 546345, 546346, 546326, 570129, 428 1, 560 65, 560 83, C09K 1912, C09K 1920, C07D23902, C07C 6976

Patent

active

058611096

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/GB94/01231, filed Jun. 7, 1994.
This invention relates to novel liquid crystal compounds, liquid crystal materials containing them and their inclusion in liquid crystal devices.
Liquid crystals can exist in various phases. In essence there are various classes of liquid-crystalline material, each possessing a characteristic molecular arrangement. For example there are nematic, cholesteric and smectic phases. A wide range of smectic phases exists, for example smectic A and smectic C. Some liquid crystal materials possess a number of liquid crystal phases on varying the temperature, while others have just one phase. For example, a liquid crystal material may show the following phases on being cooled from the isotropic phase: isotropic - nematic - smectic A - smectic C - solid. If a material is described as being smectic A then it means that the material possesses a smectic A phase over a useful working temperature range.
Devices containing ferroelectric liquid crystal mixtures exhibit fast switching times (faster than 100 .mu.s), Clark and Lagerwall, Appl. Phys. Lett., 36, 89, 1980. They can be bistable which means that they can be multiplexed at high levels using a line-at-a-time fast scan technique. Ferroelectric materials continue to receive a large amount of investigative attention due to their application in high resolution flat panel displays. An important feature of devices containing liquid crystalline materials is that they should exhibit a fast response time. The response time is dependent on a number of factors, one of these being the spontaneous polarisation, denoted Ps (measured in nC cm.sup.-2). By adding a chiral dopant to the liquid crystalline mixture the value of Ps can be increased, thus decreasing the response time of the device. Ferroelectric smectic liquid crystal materials, which can be produced by mixing an achiral host and a chiral dopant, use the ferroelectric properties of the tilted chiral smectic C, F, G, H, I, J and K phases. The chiral smectic C phase is denoted S.sub.c.sup..cndot. with the asterisk denoting chirality. The S.sub.C.sup..cndot. phase is generally considered to be the most useful as it is the least viscous. It is desirable that the material should exhibit a long pitch nematic (denoted N.sup..cndot.) and S.sub.A.sup..cndot. phase at temperatures above the chiral smectic phase in order to assist surface alignment in a device containing liquid-crystalline material. Ferroelectric smectic liquid crystal materials should ideally possess the following characteristics: low viscosity, controllable Ps and an S.sub.C phase that persists over a broad temperature range, which should include ambient temperature, and exhibits chemical and photochemical stability. Materials which possess these characteristics offer the prospect of very fast switching liquid crystal containing devices. Some applications of ferroelectric liquid crystals are described by J.S. Patel and J.W. Goodby in Opt. Eng., 1987, 26, 273.
Other smectic phases exhibit exploitable characteristics. For example the electroclinic effect, first described by S. Garoff and R. Meyer, Phys. Rev. Lett., 38, 848, (1977), usually occurs in the smectic A phase. Unlike ferroelectric devices, the liquid crystal material in electroclinic devices is not bistable. The liquid crystal director within an EC device responds almost linearly to an applied electric field. Electroclinic devices are suitable for various applications including spatial light modulators. UK Patent Application GB 2 244 566 A describes an example of an electroclinic device.
Chandani et al., Jpn. J. Appl. Phys., 27, L 729, 1988; Jpn. J. Appl. Phys., 28, L 1261, 1989; Jpn. J. Appl. Phys., 28, L 1265, 1989, first described the antiferroelectric effect which is a tri-stable switching state occurring in a liquid crystal phase designated as SmC.sub.A.sup..cndot.. For example, when ferroelectric layers are stacked so that the polarisation vectors in sequential layers oppose one another then an antiferroelectric phase is obtained.
For a

REFERENCES:
patent: 5167861 (1992-12-01), Suzuki et al.
patent: 5225105 (1993-07-01), Koseki et al.
CA 113 : 162679, 1990.

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